A method of improving fish habitat habitat by increasing diatom attachment growth

Abstract

The application provides a method for improving fish habitat environment by increasing diatom attachment growth, comprising the following processing steps: S1, placing a carrier as an attachment medium in water; S2, adding a heteropolysaccharide substance on the carrier; S3, after adding the heteropolysaccharide substance for 10-50 days, a biofilm appears on the carrier, and the biofilm contains abundant algal attachment. The application promotes the attachment growth of diatoms, green algae and other sinking algae on the surface of the carrier by placing the carrier with a bearing surface in water and adding a heteropolysaccharide substance, and by controlling the light receiving depth, attachment area and heteropolysaccharide concentration of the carrier in water. The method promotes the attachment growth of diatoms and other algae by using the heteropolysaccharide and nutrient salts in water, realizes the absorption and utilization of nutrient salts such as nitrogen and phosphorus in water, obtains attached algae such as diatoms, and achieves the purpose of improving the fish habitat environment. The application is suitable for different water environments such as seawater, freshwater and brackish water.

Description

Technical Field

[0001] This invention relates to the field of fish habitat modification and restoration, and particularly to microalgae in eutrophic water bodies and water quality control methods; specifically, it relates to a method for improving fish habitat by increasing diatom attachment and growth. Background Technology

[0002] Phytoplankton is an ecological concept referring to tiny plant organisms that live in water by floating on the surface. It typically refers to planktonic algae, including eight phyla: cyanobacteria, green algae, diatoms, chrysophytes, xanthophytes, dinoflagellates, cryptophytes, and euglena. There are approximately 40,000 known species of algae worldwide, of which about 25,000 are freshwater algae. Phytoplankton possess chlorophyll or other photosynthetic pigments, absorbing light energy and carbon dioxide to perform photosynthesis and synthesize organic matter; their size typically ranges from 2 to 200 micrometers. Phytoplankton is often referred to as microalgae, a term widely used in scientific literature and everyday communication. Microalgae are important primary producers in various aquatic ecosystems such as ponds, lakes, rivers, and oceans. Their biomass and community structure are fundamental indicators affecting the structure and function of water bodies, are important elements influencing fish habitats, and are significant contributors to the aquatic food chain. In terms of ecological function, microalgae are responsible for nearly half of the world's photosynthetic carbon sequestration, forming the basis of the aquatic food chain. They are also sensitive to changes in water quality and can serve as indicator organisms for aquatic health. Microalgae are the foundation of aquatic food webs and major producers of dissolved oxygen. The quality of their community structure directly determines the health of aquatic habitats, thereby affecting the survival, growth, and reproduction of fish.

[0003] Ponds, rivers, lakes, and oceans are important natural habitats for fish. Water flow, water quality, water depth, light, and planktonic food in these areas are important factors affecting fish habitats. Changes in microalgal community structure can profoundly affect fish habitats on multiple levels, including physical, chemical, and biological aspects. This impact is usually cascading and can also affect water quality and the environmental landscape.

[0004] With eutrophication, various water bodies in my country, including ponds, rivers, lakes, and oceans, face the problem of excessive microalgae growth and decreased water transparency. This is particularly prone to causing the proliferation of harmful algae, which typically lead to algal blooms dominated by cyanobacteria in freshwater and red tides dominated by dinoflagellates in seawater. The basic process of harmful algal growth involves harmful algae gaining dominance in competition with other algae. After mass growth, they exhibit corresponding colors in the water and easily cause oxygen depletion at night. Upon decomposition, they release toxic and harmful substances, affecting the aquatic food chain, including fish, and impacting the safety of the aquatic ecosystem. Therefore, it is necessary to regulate microalgal biomass and community structure to improve fish habitats.

[0005] Various control methods have been developed to address the problem of excessive algal blooms caused by eutrophication. The fundamental control condition is to control the input of external nutrients and reduce the level of eutrophication (source control and pollution interception). This includes effectively treating domestic sewage, industrial wastewater, and agricultural non-point source pollution (fertilizers, livestock and poultry farm wastewater) within the watershed to reduce the nutrient load on the water body. Once the nutrient load is under control to a certain extent, biological and physical methods can be used to regulate the microalgal community structure through multiple pathways.

[0006] Existing control methods include abiotic and biological control. Abiotic control includes hydrological control such as increasing water flow / disturbance and optimizing water level, as well as control of light and transparency, and nutrient ratio. Biological control includes protecting and cultivating large zooplankton, implementing "classical biomanipulation," and introducing microbial competition. When using large zooplankton for control, cultivating large zooplankton such as cladocerans and copepods can effectively feed on small green algae and some cyanobacteria. Furthermore, stocking apex predatory fish such as mandarin fish and bass can control small fish and prevent the overpopulation of small fish (such as minnows and topmouth gudgeons), as these fish consume large amounts of zooplankton.

[0007] There are various methods for implementing the above control measures. For example, when controlling microalgae through physical and hydrological means, aerators, flow promoters, or hydraulic systems can be used to break up water stratification, inhibit the upwelling and aggregation of cyanobacteria, promote nutrient cycling, and benefit the growth of diatoms that require mixed conditions. When using filter-feeding fish to control microalgae, silver carp and bighead carp can be scientifically introduced (usually in a ratio of 3:1 to 4:1), with the density precisely calculated based on the eutrophication level of the water body (e.g., 50-150 fish / acre). Silver carp can efficiently filter-feed cyanobacteria, while bighead carp feed on large zooplankton; the two work together to control microalgae biomass. When using integrated habitat restoration, ecological buffer zones (a combination of emergent and submerged plants) can be constructed in shallow water areas to stabilize the substrate, absorb nutrients, provide spawning grounds and refuges for fish, and create a symbiotic system of "aquatic plants-algae-fish". Artificial reefs and substrates can also be used to provide a growth substrate for attached diatoms (such as *Navicula*) while improving the habitat of benthic organisms.

[0008] With the vigorous development of nature by humans, various aquatic habitats have been affected. Disruptions from numerous human factors, such as water conservancy projects, overfishing, water pollution, and shipping, have led to the destruction of habitats for many fish species, resulting in the decline of fishery resources. Therefore, fish habitat restoration has become an important component of aquatic ecological restoration, leading to the development of various technologies. These include physical structure restoration technologies such as artificial reefs, riverbed morphology reshaping, and substrate modification; vegetation ecological restoration technologies such as aquatic plant restoration and shoreline ecological transformation; and water quality and microhabitat optimization technologies such as ecological floating islands and artificial aeration. Fish habitat restoration is shifting from single engineering measures to a comprehensive model of "natural solutions + technological intervention," requiring further integration of ecology, engineering, and socioeconomics to achieve sustainable aquatic ecosystem management. Microalgae are the most important primary producers in water bodies and are fundamental to the functioning of aquatic ecosystems; regulating the microalgal structure of aquatic bodies is beneficial to improving fish habitats.

[0009] Utilizing the attachment and growth of microorganisms and microalgae to form biofilms to reduce nutrient levels in water is a common method for improving water quality and regulating aquatic habitats, and it is widely used in ecological restoration projects. A large number of attached microorganisms easily form biofilms on the surface of a carrier, which is the core component of biofilm formation and plays a crucial role in the aquatic environment. The carrier's material, surface roughness, strength, and density directly affect the water treatment effect. Numerous studies have investigated carriers made of different materials, such as mesh, artificial aquatic plants, and naturally grown reeds, palm flakes, and branches. Different attachment carriers (i.e., substrates, media) produce different biofilm attachment effects due to internal and external environmental factors. Under in-situ conditions, the water purification effect of the carrier is influenced not only by the carrier's inherent characteristics but also by various other factors, such as water temperature, water depth, water transparency, water nutrients, and water flow velocity, as well as the carrier's placement depth, density, angle, and orientation in the water.

[0010] The common method of placing carriers is vertical hanging, allowing them to hang naturally under their own weight. This natural hanging method requires no external force, but it is not conducive to accumulating some sedimentary algae in the water. Sedimentary algae tend to sink to the bottom, where insufficient light exposure often hinders their growth. While this natural hanging method is advantageous for aligning with water flow and requires no additional energy, it is not conducive to accumulating large quantities of naturally settling substances. Therefore, it is worth considering changing the carrier hanging method and using substances that promote algae attachment and growth to increase the number of attached algae.

[0011] Diatoms are a type of algae that readily attach and grow, capable of both planktonic and attached growth in nature. Numerous studies have shown that diatoms secrete polysaccharides during their growth, which facilitates their attachment and growth. Existing research indicates that diatoms can attach and grow within colonies of cyanobacterial cells (the main component of which is polysaccharide); furthermore, adding agar (a polysaccharide) to sediments and then hydrodynamically disturbing the sediment promotes the large-scale attachment and growth of diatoms, using nutrients from the sediment as a substrate and agar as an attachment medium.

[0012] Making full use of the characteristics of diatoms' easy attachment and growth in aquaculture or fish habitat restoration would be of great significance, but there is still a lack of relevant research or method reports on how to apply it in practice. Summary of the Invention

[0013] The technical problem this invention aims to solve is to provide a method for improving fish habitats by increasing diatom attachment and growth, thereby enriching pathways for the transfer of matter and energy in aquatic environments, increasing beneficial algae in fish habitats, reducing nutrient levels in water bodies, and improving fish habitats. This invention is suitable for various aquatic environments, including seawater, freshwater, and brackish water.

[0014] The technical problem it aims to solve can be addressed through the following technical solutions.

[0015] A method for improving fish habitat by increasing diatom attachment and growth, the method comprising the following steps: S1. Place a carrier (i.e., an attachment medium) in the water; S2. Add heteropolysaccharides to the carrier; S3. After adding heteropolysaccharides to the carrier for 10 to 50 days, a biofilm appears on the carrier, which contains abundant algae, especially diatoms.

[0016] The algae growing on the carrier include species from the diatoms, green algae, and even some cyanobacteria, with diatoms often being dominant. When diatoms grow densely, forming brown spots or patches, the diatom cell density can reach as high as 8.6 × 10⁻⁶. 7 cells / cm 2 .

[0017] in, In step S1, the carrier can be a variety of natural organic materials or artificial materials, such as palm leaves, dried branches, plastic, glass, stone, concrete, bricks, or mixtures thereof; the carrier is not placed vertically in the water, but rather tilted in the water, with the tilt angle in the vertical direction preferably between 15 and 90 degrees. oThe goal is to maximize the attachment area, which is beneficial for absorbing sediment in the water and minimizing interference with water flow. The maximum depth of the carrier in the water should not exceed the water's transparency to meet the light requirements of the attached algae. To increase the attachment area, the carrier can be flat, and flat carriers can be made porous to prevent obstruction of water flow. The carrier surface can be smooth or rough; a rough surface increases the attachment area, which is more conducive to algal attachment and growth.

[0018] In step S2, before adding heteropolysaccharides to the carrier, the carrier should be placed in water for no more than 15 days to facilitate the initial formation of the biofilm. The added heteropolysaccharides include gellan gum, xanthan gum, agar, alginate, and seaweed extracts. In step S2, heteropolysaccharides can be added directly to water to form an aqueous solution; alternatively, an optimized method can be used, in which the heteropolysaccharides are first mixed with clean fine sand (particle size not exceeding 5 mm) and zeolite powder, with the mass of fine sand and zeolite powder each being 20-40 times the mass of heteropolysaccharides. Then, an appropriate amount of water is added to form a mixture, allowing the polysaccharides to adhere evenly to the surface of the fine sand and zeolite powder. This mixture is then air-dried or sun-dried into irregular clumps (clump size not exceeding 1 cm), and these clumps are then added. When adding heteropolysaccharides directly to water, the concentration of heteropolysaccharides should be 3-10 mg / L. When adding the dried clumps of polysaccharides to the surface of the carrier, the amount of mixture used should be 50-300 g / m³. 2 .

[0019] In step S3, after adding heteropolysaccharides, a noticeable biofilm can generally appear on the surface of the carrier and the surface of fine sand within 10 to 50 days. There is obvious algae attached and growing on the biofilm. Various algae such as diatoms, green algae and even blue algae will appear on the biofilm. In particular, there is a lot of diatom growth, and diatoms are prone to grow in spots and patches with high density.

[0020] When applying this technology in fish habitats, it is advisable to select areas with weak or even no hydrodynamic activity to minimize hydrodynamic interference and reduce the likelihood of polysaccharides settling to the bottom. Furthermore, the placement depth of the carrier should not exceed the water's transparency to meet the light requirements for microalgae growth, facilitating the absorption and utilization of nutrients in the water and achieving the dual goals of water purification and promoting algal attachment and growth.

[0021] The successful implementation of this technical solution relies on three key factors: tilted placement of the carrier (facilitating the collection of settling algae), the addition of an appropriate amount of heteropolysaccharides, and a suitable placement depth of the carrier. Furthermore, the method of adding heteropolysaccharides also affects the enrichment and growth of attached algae. Tiltped placement of the carrier facilitates the collection of settling diatoms and green algae in the water, especially easily settling diatoms, promoting diatom cell attachment and growth. Heteropolysaccharides possess a certain degree of viscosity and have a suitable molecular weight, making them an excellent attachment medium for attached algae, particularly attached diatoms. Heteropolysaccharides also provide nutrients for diatom attachment and growth; simultaneously, algae utilize dissolved carbon, nitrogen, phosphorus, silicon, and other nutrients in the water, providing conditions for the attached growth of beneficial algae such as diatoms. A suitable placement depth of the carrier in the water allows it to receive appropriate light levels towards the water surface, meeting the light requirements of the attached algae. Diatoms and other easily attached algae utilize basic conditions such as nutrients in the water, weak light, and water temperature to grow together with bacterial communities to form a biofilm. This can reduce the nutrient content in the water and compete with planktonic microalgae for nutrients, increasing the spatial density of algae growth. It can also improve water transparency to some extent, thereby improving the habitat of fish.

[0022] Compared with existing technologies, the beneficial effects of this invention are: it can increase the surface area for algae attachment and promote the attachment and growth of beneficial algae such as diatoms and green algae, especially diatoms, because diatoms and green algae have settling properties and are supported by an inclined carrier during the settling process, which is conducive to their growth and attachment. Compared with existing technologies, the beneficial effects of this invention are: 1. It was found that heteropolysaccharides such as gellan gum, xanthan gum, agar, alginic acid, and alginate are significantly beneficial to the attachment and growth of algae such as diatoms, and improve the attachment efficiency of algae.

[0023] 2. It can increase the surface area for algae to attach, and can also increase the attachment and growth of beneficial algae such as diatoms and green algae, especially the attachment and growth of diatoms.

[0024] 3. Fine granular substances such as fine sand and zeolite powder can be mixed with the above-mentioned heteropolysaccharides to promote the growth of attached algae, especially attached diatoms. The effect of using them together to promote the attachment and growth of algae is better than using heteropolysaccharides alone. Attached Figure Description

[0025] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: all algae photographs in the embodiments were taken under an optical microscope. The invention is suitable for various aquatic environments, including seawater, freshwater, and brackish water.

[0026] Figures 1-6The images show algae, mainly diatoms, attached to the plexiglass plate in Process III of Example 1. All images were taken at 400x magnification.

[0027] Figures 7-11 This is a representative photo of the algae in the brown area of ​​the brick with added dry matter in Example 2. It mainly shows some small diatoms, spherical cyanobacteria and a small amount of filamentous cyanobacteria growing in clumps. Figures 12-18 These are representative photographs of algae in the dark green areas of the bricks on which dry matter was added in Example 2. They mainly consist of clumps of green and blue algae. All photographs were taken at 400x magnification.

[0028] Figures 19-23 These are photographs of the dense growth of diatoms in treatment III of Example 3; Figures 24-26 This is a photo of diatoms after their fine granular cell clusters have been broken up; Figures 27 to 30 These are photographs of diatoms growing on the sodium alginate surface treated in Example 3. All photographs were taken at 400x magnification.

[0029] Figures 31-50 These are the algae photographs corresponding to the processing in Example 4, wherein... Figure 46 , Figure 47 One photo was taken at 100x magnification, while the others were taken at 400x magnification. Detailed Implementation

[0030] Based on the current state of the technology, the inventors of this application have discovered a method to improve the habitat of fish by increasing the attachment and growth of diatoms. Its main feature is that by controlling the light exposure depth, attachment area and heteropolysaccharide concentration of the carrier in the water, the attachment and growth of sedimentary algae such as diatoms and green algae can be promoted. In other words, heteropolysaccharides can achieve the enrichment and growth of attachment algae such as diatoms.

[0031] In practice, the addition of heteropolysaccharides has a significant effect on the enrichment and growth of diatoms and other attached algae. The amount of attached biomass of diatoms and other algae is related to factors such as water environment conditions and season. The algal density and community structure of the water body itself, water temperature, hydrodynamics, light, nutrient level, and transparency all affect the attachment and growth results of specific algae.

[0032] This invention provides a method for improving fish habitats by increasing diatom attachment and growth. This involves placing a carrier with a receiving surface in water, then adding heteropolysaccharides to the carrier. By controlling the light exposure depth, attachment area, and heteropolysaccharide concentration of the carrier in the water, the method promotes the attachment and growth of sedimentary algae such as diatoms and green algae on the carrier surface. After static cultivation for 10-50 days, a large number of algae, especially diatoms, can be obtained attaching and growing on the carrier surface. The cell density of the attached diatoms, exhibiting a speckled growth pattern, can reach as high as 8.6 × 10⁻⁶ cells / day. 7 cells / cm 2This method utilizes heteropolysaccharides and nutrients in the water to promote the attachment and growth of algae such as diatoms, thereby achieving the absorption and utilization of nutrients such as nitrogen and phosphorus in the water, obtaining attached algae such as diatoms, and ultimately improving the habitat of fish.

[0033] The present invention will be further described and illustrated in detail below with reference to specific embodiments and accompanying drawings, with more specific implementation methods. Example 1: Cultivation of attached diatoms in a glass tank inside a glass greenhouse.

[0034] Building upon existing methods for cultivating attached diatoms using agar and sediment (Wang Xiaodong, Che Xuan, Liu Xingguo, Li Yiming, Wang Hong, Lu Shimin. A method for cultivating diatoms using sediment in a resource-efficient manner. Patent Application No.: 202410935167.0), the inventors further explored high-density cultivation methods for diatoms. In particular, they utilized the characteristic of heteropolysaccharides as a suitable medium for diatom attachment, further integrating these methods with applications such as aquaculture and fish habitats to promote multiple functions and improve diatom growth.

[0035] In mid-October, as the weather gradually cooled, the brownish-yellow tailwater from tilapia farming in a greenhouse was diluted with tap water at a volume ratio of 1:5. The resulting water was light brownish-yellow, with almost no phytoplankton and a total nitrogen concentration reduced to approximately 20 mg / L. Aeration was then introduced to cultivate phytoplankton. After 20 days of cultivation, the water turned light yellowish-green, and phytoplankton growth was observed. After another 10 days of cultivation, the water color deepened to a light brownish-yellowish-green. Microscopic examination revealed diatoms (mainly nigrum and boat-shaped algae) and green algae (such as fibrous algae, Scenedesmus, and Chlorella), with the chlorophyll a (Chla) concentration reaching 356.0 μg / L.

[0036] Then, in a glass greenhouse, the water rich in cultured algae was introduced into colorless, transparent glass tanks (60cm x 40cm x 40cm) for a new algae cultivation experiment. Four treatments were established (Table 1). The influencing factors for each treatment were the phytoplankton concentration and the concentration of gellan gum added. The phytoplankton concentration was obtained by diluting with tap water to achieve a lower concentration. The water depth in each tank was 37cm. A piece of acrylic sheet (39cm long, 15cm wide) with circular holes was placed at an angle in each tank, ensuring that the top of the sheet was completely submerged in water. The gellan gum used was produced by Beijing Wokai Biotechnology Co., Ltd., with a density of 0.32~0.45g / cm³. 3It is a white powder, soluble in water. When adding gellan gum to each tank, use a 2.0 g / L gellan gum stock solution prepared two days in advance. To prepare the 2.0 g / L gellan gum stock solution, stir for 10 minutes and let it stand for two days to allow the gellan gum to disperse as much as possible in the water before adding it. Allow to stand for incubation. During incubation, add tap water every 3-5 days to maintain a stable water volume in the glass tank.

[0037] In mid-November, as temperatures gradually decreased, phytoplankton growth was not observed in any of the tanks, possibly due to the lower temperatures. However, after 15 days, the surface of the acrylic glass plates became rough, and algae attachment became apparent, though not evenly distributed. After 30 days, algae attachment was more pronounced on the upper surface of the acrylic glass plates near the water surface, while the surface became smoother towards the bottom. This suggests that the algae on the acrylic glass plates was not merely settling, but rather growing. If it were purely settling, the algae distribution on the surface would be more uniform. Furthermore, since water depth affects light conditions, the algae attachment and growth on the acrylic glass plates are related to light exposure. The upper part of the acrylic glass plates, closer to the water surface, receives more light, while the lower part receives less light. This difference in light intensity at different depths leads to variations in the amount of algae attached to the acrylic glass plates.

[0038] Table 1. Phytoplankton Chla concentration and added gellan gum concentration at the initial stage of the experiment for different treatments. Processing Number Phytoplankton Chla concentration (μg / L) Gellan gum concentration (mg / L) I 356.0 8.0 II 356.0 4.0 III 119.0 8.0 IV 119.0 4.0 Furthermore, based on visual inspection, treatment III, with its initial low algae concentration and high concentration of gellan gum, exhibited the most significant algae attachment. At 35 days, each plexiglass plate was removed from the water, and a certain area of ​​the attached algae was scraped off for microscopic examination and density counting. Microscopic observation revealed that the types of attached algae were essentially the same across treatments; the main difference lay in the attachment density. Treatment III showed the highest algae density on the plexiglass plates. Fresh samples were photographed under a 400x microscope; details are shown below. Figures 1 to 6 It is evident that the attached algae are of various types, including diatoms such as *Nyctaginea*, *Navicula*, and *Heteromorpha*, as well as cyanobacteria such as *Chromococcus* and *Cyanobacteria*, and *Cladosporium*, among others. The total attached algal density reached a maximum of 9.3 × 10⁻⁶. 5 cells / cm 2 The highest adhesion density of diatoms reached 5.1 × 10⁻⁶. 5 cells / cm 2 .

[0039] It is evident that diatoms are abundant among the attached algae. In terms of diatom cell count, various diatoms account for as much as 55% of all cells. Furthermore, the diatom cells observed in this culture experiment are significantly larger than those of other algal phyla. Therefore, if converted to biomass, the proportion of diatom biomass would be even higher. This indicates that supplementing with heteropolysaccharides can promote the attachment and growth of settled algae, particularly benefiting the attachment and growth of diatoms. Example 2: Attached diatoms culture in a small pond.

[0040] Using 50g of clean fine sand (particle size 0.5-3 mm), 30g of zeolite powder, and 1.5g of gellan gum solid powder, mix well and add about 40mL of tap water. Stir again to allow the gellan gum, which becomes viscous and transparent after absorbing water, to adhere as evenly as possible to the fine sand particles and zeolite powder. Then, form these gellan gum-coated sand and zeolite powder into clumps about 0.5-1cm in size, spread them out, and air dry them for later use. This clump-shaped dry matter is called substance A.

[0041] Meanwhile, using 50g of clean fine sand (particle size 0.5-3 mm), 30g of zeolite powder, and 1.5g of sodium alginate solid powder, mix well and add about 40mL of tap water. Stir again to ensure the sodium alginate, which becomes viscous and transparent after absorbing water, adheres as evenly as possible to the fine sand particles and zeolite powder. Then, form these sodium alginate-coated sand and zeolite powder into clumps about 0.5-1cm in size, spread them out, and air-dry them for later use. These clumps of dried substance are designated as Substance B. The sodium alginate used is produced by Sinopharm Chemical Reagent Co., Ltd., and is a pale yellow powder soluble in water.

[0042] There is a small ornamental pond (circular, 5m in diameter, 1m deep) in an office park. Some koi carp, each weighing approximately 200-300g, are raised in the pond. The water has a transparency of about 55cm, a yellowish-green color, and a variety of phytoplankton, including green algae, cyanobacteria, and diatoms. Examples of green algae include *Chlorella vulgaris*, *Scenedesmus*, *Fibrophyta*, and *Oocystis*; cyanobacteria include *Microcystis aeruginosa*, *Chlorella*, and *Microcystis*; and diatoms include *Navicula* and *Cyclocarya*. Green algae are clearly dominant in number.

[0043] In mid-September, when the weather is relatively hot, two relatively intact, similarly sized, porous, dark red bricks were selected from construction waste. After cleaning them thoroughly with tap water, they were suspended in the water of a small pond using ropes, ensuring that the larger side of the brick was parallel to the water surface, with the top surface of the brick 20cm above the water. The two bricks were placed close together to ensure similar light exposure. On the top surface of one brick, two pieces of the pre-prepared dry matter A and two pieces of the pre-prepared dry matter B were placed, and these two different substances were distinguished by marking them on the brick, keeping them as far apart as possible. The surface of the other brick was left empty, without placing dry matter A or B on it.

[0044] Every week or so, I checked the algae growth on the surfaces of the two bricks at the pond's edge, gently lifting them out of the water for careful observation. Generally, a small amount of algae deposits appeared on the surface of both bricks within the first week, but not much. By the third week, more noticeable algae growth was observed on the brick surfaces, especially on the bricks with added dry matter, although the growth was uneven. After nearly 50 days of cultivation, the algae growth on the bricks with added dry matter A and B was very pronounced, particularly on the dry matter itself, with brown or dark green patches of algae. The bricks without added dry matter A and B also had a light brownish-green substance on their surface, but less noticeable than the other brick. Furthermore, the algae growth was even less pronounced on the sides of both bricks, the surfaces perpendicular to the water surface.

[0045] Therefore, substances were scraped from the surface of two bricks and observed under a microscope, especially those bricks with added dry substances A and B. During scraping, the attached substances were wiped with a clean white gauze strip and rinsed with approximately 30 mL of clean tap water. After settling for one hour, the freshly precipitated algae were observed under a microscope. Figures 7-11 This is a representative photograph of the algae in the brown area on a brick with added dry matter. It shows mainly clumps of small diatoms, spherical cyanobacteria, and a small amount of filamentous cyanobacteria, as well as some larger green algae, with diatoms being the most numerous. Because these attached algae cells are very dense and grow in clumps, the cell density is difficult to calculate accurately. Preliminary calculations indicate that the diatom cell attachment density in the densely packed diatom areas reaches at least 7.6 × 10⁻⁶. 7 cells / cm 2 .

[0046] Figures 12-18These are representative photos of algae in the dark green areas of bricks with added dry matter. They mainly consist of clumps of green and blue-green algae, with the green algae cells being much larger than the blue-green algae cells. There are also some filamentous blue-green algae. The types of algae attached to the surface of bricks without added dry matter are similar to those on bricks with added dry matter, but the amount attached is significantly less.

[0047] It is evident that the addition of dry matter A and B significantly promotes the attachment and growth of algae on the brick surface, resulting in a significant increase in diatoms and green algae, as well as spherical and filamentous cyanobacteria. This indicates that the addition of heteropolysaccharides can promote the attachment and growth of diatoms. The increased number of attached algae facilitates the utilization of nutrients, reduces nutrient levels in the water, improves water transparency, and provides a better habitat for fish.

[0048] Example 3: Experiment on culturing diatoms directly using heteropolysaccharides.

[0049] To further investigate the promoting effect of viscous heteropolysaccharides on diatom growth, diatom culture experiments were conducted using viscous heteropolysaccharides. The experiments were carried out in an air-conditioned office room. On weekdays, the air conditioning was on from approximately 9:00 AM to 5:00 PM, maintaining a room temperature of approximately 20-25°C. The air conditioning was turned off at night, with the nighttime minimum temperature around 5°C, generally between 10-15°C. The experiments began in mid-December, when the weather was colder. During weekends and the Spring Festival, the air conditioning was also not used during the day, resulting in lower temperatures.

[0050] The substances used for cultivation are substances A and B from Example 2, and are mixed into granules using the same clean fine sand and zeolite powder in a mass ratio of 5:3 as in Example 2. This substance does not contain sodium alginate and does not clump together; this substance is referred to as substance C.

[0051] Diatom culture experiments were conducted using 250mL Erlenmeyer flasks, each containing 200mL of tap water (untreated). 20mL of a pre-concentrated high-concentration diatom stock solution was added to each flask. The diatom strains in this stock solution were derived from aquaculture ponds and cultured on a culture medium prepared by the inventor. The main diatom species was a small *Pterygota* species, with a small amount of *Navicula* mixed in. After adding the stock solution, the diatom cell concentration in each flask was approximately 5.0 × 10⁻⁶. 5 cells / mL. During culture, the cells were divided into 1 control group and 5 treatment groups based on the type and quantity of added substances (Table 2), with 3 replicates for each treatment.

[0052] During the cultivation period, careful observation was conducted. In treatments I, II, and III with added substances A and B, the dry matter, after absorbing water, remained in clumps but gradually dispersed. Due to the lack of disturbance and static cultivation, some transparent, viscous clumps formed after sodium alginate dissolved in water settled to the bottom. For the first 7 days, apart from the diatoms settling and the water gradually becoming clearer, no other significant changes were observed in any treatment. Around day 10, some changes gradually appeared, especially in treatments I, II, and III with added substances A and B. Dark brown fine spots gradually appeared on the clumps, particularly in treatments II and III. No obvious brown fine spots appeared in treatment IV. No significant algal growth was observed in the control group. In the culture flask containing mixture A of sodium alginate, fine sand, and zeolite powder, due to the lack of shaking, both the culture material and the added diatoms clearly settled to the bottom, and the water became clear.

[0053] On day 25, the dark brown fine spots from treatment III were examined under a microscope and found to be densely growing diatoms. Figures 19 to 23 The increased density of diatoms after clustering indicates its advantage in promoting diatom growth. The control group showed no significant algal growth. These fine diatom cell clusters were then broken up and photographed. Figures 24 to 26 ); calculations show that the density of these diatoms aggregated into fine granular clusters reaches 8.6 × 10⁻⁶. 7 cells / cm 2 .

[0054] In treatment V, where only sodium alginate was added, no obvious brown diatom particles formed; some culture flasks showed a small amount of light brown material on the surface of the settled sodium alginate particles. Microscopic observation also revealed diatom growth, but the growth was not as dense as in treatment III. Figures 27 to 30 However, it is evident that the diatom cells grow very well side-by-side through the gelatinous layer. Meanwhile, the inner walls of each culture flask were very clean, with no obvious polysaccharide or algal adhesion or growth. This is likely related to the fact that the tilt angle of the inner walls is not conducive to collecting algae and other substances added to the water. The bottom of the culture flask is conducive to collecting settled algae and other substances, thus facilitating the growth of algae attached to the bottom material after sedimentation.

[0055] Table 2 Design of each experimental treatment Processing Number Added substances Mass of added dry matter (g) Sodium alginate concentration (mg / L) Comparison none 0 0 I A 0.42 0 II A 0.9 0 III B 0.95 0 IV C 1.02 0 V Sodium alginate 0 8.0 This example demonstrates that sodium alginate, mixed with fine sand and zeolite powder, can be used to directly cultivate attached diatoms in tap water, indicating that sodium alginate, a viscous polysaccharide, can provide a medium and nutrients for diatom growth. This is also why viscous heteropolysaccharides can be used to enhance the attachment and growth of diatoms in natural algal communities with mixed algae. Viscous heteropolysaccharides possess a certain degree of viscosity, providing an attachment medium for easily attached algae such as diatoms. Simultaneously, viscous heteropolysaccharides may promote algal growth by enriching some nutrients in the water.

[0056] Because algae such as diatoms are rich in nutrients and can be used as high-quality live food for fish and shrimp, they can improve the food supply in fish habitats. At the same time, these attached algae can absorb nutrients such as nitrogen and phosphorus in the water, which helps to reduce the nutrient level in the water and can control the eutrophication level of the water to a certain extent, thus improving the water quality of fish habitats and achieving the goal of improving fish habitats.

[0057] This example of diatom cultivation demonstrates that viscous heteropolysaccharides are effective in directly culturing diatoms. However, culturing viscous heteropolysaccharides directly in water is less effective than adding fine sand and zeolite powder. Cultivating diatoms with viscous heteropolysaccharides in combination with some particulate matter yields better results, possibly because these particles increase the surface area.

[0058] This study investigated a circular tank biofloc culture system for tilapia in a greenhouse (tank depth approximately 80 cm, diameter 3 m). The system contained abundant, light brown bioflocs, primarily composed of bacterial clumps and filamentous algae, with minimal diatom biomass and only occasional small numbers of diatom cells. The biofloc concentration was determined using a 1 L Inhofe conical tube. After allowing 1 L of water to stand for 0.5 hours, a sediment volume of 2.0 mL was obtained, indicating a biofloc concentration of 2.0 mL / L. In late October, the water was transferred to a 30cm x 30cm x 30cm colorless transparent glass tank. Three smooth, relatively flat pebbles, each 5-8cm in size, were placed in the tank. Two of the pebbles had a 1cm clump of dried alginate mixed with fine sand and zeolite powder (used in Example 2) placed on their surface. The third pebble was left untouched by the dried alginate mixture. The tank was left to stand undisturbed.

[0059] Without disturbance, the bioflocs in the glass tank sank noticeably within 2 hours, and the water became clearer, though still a light brownish-yellow color. Continued observation was maintained. After one week, the fine suspended matter in the water decreased further, the water became clearer, and obvious flocculent sediment appeared on the surface of the pebbles. After two weeks, the sediment on the pebble surface became even more pronounced. After one month, the flocculents on the pebble surface with added dried substance B were light brownish-yellow-green, and in some areas a thin, dense layer of brown deposits appeared. Scraping a fresh sample and observing it under a microscope revealed a large number of bacteria, filamentous algae, and well-grown diatoms and some green algae. Figures 31-39 Some sodium alginate can still be seen as transparent fine granules, with a small amount of green algae and diatoms attached and growing on them. Figures 40-41 In particular, the thin layer of brown deposits is diatoms of very high purity. Figures 42-47 Diatom cells are relatively large, reaching 25 μm in length, and exhibit a distinct radial growth pattern. These diatom cells are primarily *Nyctaginosa* and *Heteromorpha*. *Nyctaginosa* and *Heteromorpha* are common diatoms in eutrophic waters that readily attach and grow. Bioflocs also deposited on the surface of pebbles without the addition of dried substance B, but these contained fewer diatoms and were greener in color, primarily consisting of bacteria. The green color is due to the increased growth of green algae. Figures 48-50 ).

[0060] The comparison of attached algae growth with and without the addition of dried substance B shows that more algae grow on the pebbles after the addition of dried substance B, especially diatoms. While there are some diatoms on the attached algae without the addition of dried substance B, the number of diatoms is relatively small.

Claims

1. A method for improving fish habitat by increasing diatom attachment and growth, characterized in that, The following processing steps are included: S1. Place a carrier in water as an attachment medium; S2. Add heteropolysaccharides to the carrier; S3. After adding heteropolysaccharides for 10 to 50 days, a biofilm appears on the carrier, and the biofilm contains abundant algae.

2. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S1, the carrier is a natural organic material, an artificial material, or a mixture thereof.

3. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1 or 2, characterized in that: In step S1, the carrier is one or a mixture of more than one of palm leaves, dried branches, plastic, glass, stone, concrete or brick.

4. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S1, the carrier is placed at an angle in the water, with an angle of inclination of 15 to 90 degrees relative to the vertical direction.

5. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S1, the maximum depth at which the carrier is placed in the water does not exceed the water's transparency.

6. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S1, the carrier is in the form of a flat plate or a porous flat plate.

7. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S1, the carrier surface is a rough surface that can increase the adhesion area.

8. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S2, the carrier is placed in water for no more than 15 days before the heteropolysaccharide is added to the carrier.

9. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1 or 8, characterized in that: In step S2, the added heteropolysaccharide is one or more of gellan gum, xanthan gum, agar, alginate, or alginate.

10. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S2, the heteropolysaccharide is directly added to water to form an aqueous solution, or it is added to water in a clump form after adhering to the surface of a mixture of fine sand, zeolite powder and water.

11. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 10, characterized in that: Before addition, the clump-like shape adopts the following forming rules: 1) Mix clean fine sand with a particle size not exceeding 5 mm with zeolite powder, and mix them in a ratio of 20 to 40 times the mass of the heteropolysaccharide material, respectively. Then add an appropriate amount of water to form a mixture. 2) The heteropolysaccharide material is evenly adhered to the surface of the mixture and then air-dried or sun-dried into irregular clumps no larger than 1 cm in size.

12. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 10, characterized in that: In step S2, when adding heteropolysaccharides directly to water, the concentration of heteropolysaccharides is controlled at 3~10 mg / L; when added in dry, lumpy form, the amount of lumpy material used on the carrier surface is controlled at 50~300 g / m³. 2 .

13. The method for improving fish habitat by increasing diatom attachment and growth as described in claim 1, characterized in that: In step S3, the algae attached to the biofilm include one or more of diatoms, green algae, or blue-green algae; the attached diatoms grow in high density in the form of spots and / or patches.

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