Growth of Red Abalone,Haliotis rufescens,Fed Cold‐stored Benthic Diatoms

We measured the proximal composition of four benthic diatoms that were stored for 24 mo in the dark at low temperature (4 C by refrigeration) and examined their potential as feed for abalone, Haliotis rufescens, postlarvae. The proximal composition of the four diatoms was modified by species‐specific responses as a function of time in storage. The cultures of all stored diatoms contained low or undetectable concentrations of Vibrio‐like bacteria (<0.01 VLB/mL). As feed for abalone postlarvae, the four diatoms promoted growth under all experimental conditions. Greater shell lengths were measured on Day 14 when Navicula sp. and Navicula incerta were used as feed. Postlarvae that were fed N. incerta and Navicula sp. had higher growth rates. In contrast, lower growth rates were observed on Day 7 with fresh and stored Nitzschia thermalis as food. Survival was high in postlarvae that were fed the four stored diatoms (100%). This report demonstrates that cultures of benthic diatoms that have been stored by refrigeration for 24 mo can be used to feed abalone postlarvae and have an effect on improving growth and survival.     

Cold Storage of Six Marine Benthic Diatoms Native to the Mexico Pacific Coast

Cultures of six benthic diatoms were maintained in the dark to measure their viability and biochemical composition after 8 wk of storage at low temperature (4 C) in darkness by refrigeration. Cell density, growth rate, and viability for each benthic diatom changed significantly after storage. Significant differences were observed with regard to cell size (length and width) of Nitzschia laevis, Navicula sp., and Amphora tenerrima as a result of storage. In general, the proximal composition of the benthic diatom cultures changed after week 1 of storage and decreased after week 4 of storage for all the diatoms. These results demonstrate that under 1–4 wk of storage these diatoms maintain their viability and had changes in their proximal composition in species‐specific responses. Storage of preserved live microalgae cells is an alternative technique that can be used to reduce the need for continuous maintenance of live cultures and can provide live feed stock for aquaculture applications.     

Effects of addition of Navicula sp. (diatom) in different densities to postlarvae of shrimp Litopenaeus vannamei reared in a BFT system: Growth,survival, productivity and fatty acid profile

The objective of this study was to evaluate the effect of the addition of Navicula sp. on the growth and fatty acids profile of Litopenaeus vannamei postlarvae in a biofloc system (BFT). Four treatments were used: BFT; BFT 2.5N (addition of 2.5 × 10⁴ cells/ml of Navicula sp.); BFT 5N (addition of 5 × 10⁴ cells/ml of Navicula sp.) and BFT 10N (addition of 10 × 10⁴ cells/ml of Navicula sp.), all in triplicate. The shrimp (1 ± 0.01 mg) were stocked at a density of 3,000 postlarvae/m³ and fed with commercial feed. The diatom was added every 10 days, and at the end of 42 days, shrimp performance, water quality and proximal composition were evaluated. The BFT 5N and BFT 10N treatments had higher performance values, highlighting the values of productivity (2.30 and 2.42 kg/m³) and specific growth rate (15.92 and 16.08%/day), which were higher than the other treatments. In addition, the highest levels of fatty acids were observed in treatments with diatom (BFT 5N and BFT 10N), indicating the benefits of Navicula sp. on growth enhancement and fatty acid content of L. vannamei postlarvae grown in biofloc systems.     

Effect of the addition of Chaetoceros calcitrans,Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and growth of Litopenaeus vannamei (Boone) postlarvae reared in a biofloc system

The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system . Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT‐F (biofloc system with feed and no addition of diatoms); BFT‐D (biofloc system with the addition of diatoms and no feed); and BFT‐FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m^?3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 10⁴ cells mL^?1 for each species. No significant differences (P > 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (P < 0.05) were observed for nitrite, orthophosphate, alkalinity, final weight, weight gain, yield, feed conversion ratio (FCR), phytoplankton and cyanobacteria composition. The BFT‐FD treatment had better performance parameters for final weight (270 mg), weight gain (254 mg), yield (0.67 Kg m^?3) and FCR (0.61), indicating the benefits of the diatoms C. calcitrans, Navicula sp. and P. tricornutum for decreasing cyanobacteria and improving growth of L. vannamei postlarvae reared in biofloc systems.     

Effects of salinity on the growth and proximate composition of selected tropical marine periphytic diatoms and cyanobacteria

Marine periphytic cyanobacteria and diatoms have been examined as a potential source of feed supplement for rearing aquatic larvae in the aquaculture industry. Culture of the periphytic diatom Amphora sp., Navicula sp., Cymbella sp. and the cyanobacteria Oscillatoria sp. at different salinities showed significant changes in biomass and specific growth rates. Diatoms growth was significantly higher at 35 g L⁻¹, while for cyanobacteria growth was better at 25 g L⁻¹. Significantly higher levels of protein and lipid were found in diatoms at low salinities (15–25 g L⁻¹) and an increase in carbohydrate at high salinities (30–35 g L⁻¹). Conversely, cyanobacteria showed a significantly higher lipid content at 30–35 g L⁻¹ compared with other salinity levels but no significant changes were observed in the protein and carbohydrate contents at different salinity levels. The present findings can be taken into consideration when culturing marine periphytic Amphora sp., Navicula sp., Cymbella sp. and Oscillatoria sp. to provide appropriate levels of protein, lipid and carbohydrate as feed supplement as well as for bioremediation in aquaculture.     

The effect of nitrate supplementation on the biochemical composition of benthic diatoms and the growth and survival of post-larval abalone

Elevating the nitrogen concentration in microalgal growth media can elevate the protein content of the algae and consequently increase their dietary value to molluscs. This study examined the protein content, and dietary value to abalone post-larvae, of seven benthic diatoms acclimated to high-(“H” = 49.4 mg NO₃-N l^− 1) and standard-nitrate (“S” = 16.5 mg NO₃-N l^− 1) Walne medium. In Experiment 1, the level of nitrate in the culture medium did not significantly affect the protein content of Cocconeis sp., Cylindrotheca closterium or Nitzschia ovalis, and variation in the growth of post-larval Haliotis iris was not associated with nitrate level or the protein content of the diatoms. When the same six diatom diets were added daily as cell suspensions, growth and survival were much lower than for the equivalent strains fed as established films (P < 0.0001). In Experiment 2a, the protein content of Navicula incerta was elevated by nitrate supplementation, and the high nitrate strain retained a higher protein content (P = 0.005) even after 24 days growing in unenriched, flowing seawater. Haliotis rufescens post-larvae grew significantly faster when fed N. incerta H than when fed N. incerta S (P = 0.006) and survival was also higher with this diet (67 versus 54%). In Experiment 2b, there was no significant effect of nitrate level on protein content of four diatoms or the performance of post-larval H. rufescens. There was, however, a strong positive correlation (r = 0.95, P < 0.0001) between post-larval survival and the lipid content of the diatom diets. Post-larval growth showed positive, but marginally non-significant, relationships with diatom protein and carbohydrate, but no relationship with lipid content. Overall, only one of seven benthic diatom species acclimated to high-nitrate growth medium displayed significantly elevated protein content. Diatom protein content explained relatively little of the variation in food value of diatom strains for post-larval abalone but lipid content correlated strongly with post-larval survival.     

Culture of benthic diatoms and effect of dissolved organic carbon on metamorphosis of the ‘white sea urchin Lytechinus pictus (Verrill)’

The effect of biofilms of the benthic diatom Navicula incerta and of the dissolved organic carbon (DOC) they produce was evaluated on the growth and survival of Lytechinus pictus postlarvae during metamorphosis. In each container, 300 postlarvae were exposed to biofilms beginning on days 1, 3 and 6 of metamorphosis, using three replicates and a blank containing only filtered water. The experiments were run for 15 and 18 days in 500‐mL containers with daily water changes. We measured 30 postlarvae from each container and counted all organisms on days 1, 3, 9 and 15; DOC was quantified on days 3, 6 and 9. A second experiment was conducted to evaluate whether the presence of diatoms or the DOC they produced improved postlarval development. Five assays were performed in triplicate: a positive control with biofilms, a negative control with filtered water and three treatments with DOC‐enriched water from a N. incerta culture supplied on days 1, 4 and 8. In both experiments, postlarvae attained the largest size and highest survival in the treatments with the biofilm. The results indicate that the increase in postlarval size and survival was due to the DOC produced by the diatoms and not by their presence alone.     

Evaluation of the Microalgae Paste Viability Produced in a Mollusk Hatchery in Southern Brazil

The present study was conducted to define a methodology to produce and store small‐scale microalgae paste to be used in a mollusk hatchery. Microalgae were cultured in 500 L fiberglass tanks, under temperature of 20 ± 2 C, Guillard f/2 culture medium, and continuous light intensity of 203–226 μmol photons/m²/sec. Cultures were centrifuged at 2000 g at the exponential growth phase. Microalgae cell quality after centrifugation and during storage was determined by analyses with Evan’s blue stain and by counting the number of total marine bacteria. Treatments with and without additive were applied to the microalgae paste produced, which was distributed into 100 mL plastic containers, capped, and stored under refrigeration at 4 ± 1 C. Results indicated that in the Chaetoceros muelleri paste, centrifugation did not damage the cells and the number of total marine bacteria reduced significantly from 2.9 × 10⁶ to 8.3 × 10⁵ colony‐forming units per milliliter. Chaetoceros muelleri and Chaetoceros calcitrans pastes stored with addition of 0.1% ascorbic acid had a shelf life shorter than 2 wk. For the treatment without additive, results with Evan’s blue stain showed that cells (99%) remained viable until the sixth week of storage for C. muelleri and seventh week of storage for Skeletonema sp. and C. calcitrans. The number of bacteria did not increase during storage for C. calcitrans and Skeletonema (P > 0.05). For C. muelleri, an increase in bacteria (P < 0.05) was observed after the sixth week of storage. This study demonstrated the feasibility to produce and store microalgae paste for a period of 2–8 wk, which allows it to be used as food source and also optimizes the use of microalgae cultured in laboratory.     

Effect of inoculation of the cyanobacteria Oscillatoria sp. on tilapia biofloc culture

Cyanophytes are the most ancient photosynthetic organisms. During its evolution, they have developed various ecophysiological adaptation strategies to survive in extreme conditions. The environment prevailing under biofloc cultures provides various conditions appropriate for cyanobacterial proliferation. An outdoor experiment (7 weeks) was performed with a simple random design consisting of four inoculation levels (by triplicate) of Oscillatoria sp. (0.0, 0.1, 0.5 and 1 mg L^?1) in saltwater biofloc. The objective was to evaluate the effect of the cyanobacteria inoculation on water quality and tilapia production parameters. The results indicated that the amount of Oscillatoria sp. inoculated significantly affected water quality (pH, chlorophyll a, TSS and NO₃‐N) and tilapia parameters (final weight, feed conversion ratio, specific growth rate and survival). No significant effects on dissolved oxygen, total ammonia nitrogen (TAN) or NO₂‐N were observed. We recommend identifying the cyanobacteria species that are able to grow in a biofloc system and their possible adverse effects on the system.     

基于围隔实验研究虾夷扇贝与龙须菜养殖对浮游植物群落结构的影响

2015年秋季在桑沟湾开展围隔实验,研究了60 h内高容量虾夷扇贝(Patinopecten yessoensis)和龙须菜(Gracilaria lemaneiformis)养殖对水体中物理、化学和生物(浮游植物群落)等因素的影响。结果显示,养殖的虾夷扇贝和龙须菜在60 h内能显著改变水体中的溶解氧(DO)和溶解态无机氮(DIN)的浓度,同时,能显著影响浮游植物种群丰度和组成特征。从各实验组来看,12 h后,虾夷扇贝和龙须菜实验组浮游植物丰度显著低于空白实验组。虾夷扇贝对水体中4种硅藻优势种[包括柔弱拟菱形藻(Pseudo-nitzschia delicatissima)、双菱藻(Surirella sp.)、菱形藻(Nitzschia spp.)、针杆藻(Synedra spp.)]的滤除效应存在较大差异,即对柔弱拟菱形藻和双菱藻有较大的滤除效应,但对菱形藻和针杆藻却影响不大。基于水体中的光合色素变化特征也揭示了虾夷扇贝对浮游植物的选择性摄食效应,即虾夷扇贝能显著滤除水体中的岩藻黄素(fucoxanthin,硅藻特征色素)、别藻黄素(alloxanthin,隐藻特征色素)。与此相反,青绿藻素(prasinoxanthin,微微型藻类的特征色素)在48 h后,虾夷扇贝实验组显著高于空白实验组和大型藻实验组,说明龙须菜养殖对微微型青绿藻生物量无显著影响。     

Influence of Nitzschia sp. on release of nitrogen and phosphorus from sediment in pond breeding sea cucumbers

Due to the tonic and nutritive virtues of sea cucumbers, increased commercial aquaculture has resulted in the expansion of breeding ponds, a primary form of sea cucumber production. Expansion of such production methods has led to increased settling of organic wastes onto the seabed, resulting in enriched sediments. Nitzschia sp. serves as an edible sea cucumber feed. Release characteristics of nitrogen (N) and phosphorus (P) from sediments in the presence of different biomass densities of Nitzschia sp. were studied via laboratory static cultures. pH and dissolved oxygen (DO) in the overlying water and biochemical components (i.e., protein, chlorophyll a) of Nitzschia sp. were assessed. When the biomass of Nitzschia sp. was more than (2–5) × 10⁴ ind/cm², the release of N and P nutrients was significantly promoted; additionally, the DO content of the overlying water was relatively high and the pH was relatively stable, which favoured the accumulation of proteins and chlorophyll a in Nitzschia sp. The results indicated that Nitzschia sp. promotes the release of N and P in sediments while absorbing them to maintain their own growth and promote the accumulation of nutrients, such as proteins, for the sea cucumbers. At the same time, the algae release oxygen, increasing the DO of the overlying water, providing a healthy breeding environment for the sea cucumbers. Application of Nitzschia sp. has the potential to reduce environmental harm caused by sea cucumber cultivation and thus achieve sustainable aquaculture.     

Chilled storage of banana shrimp (Fenneropenaeus merguiensis) spermatophores with supplementation of moringa (Moringa oleifera Lam.) extract

This study was designed to optimize the chilled storage method for banana shrimp (Fenneropenaeus merguiensis) spermatophores and evaluate the potential of moringa (Moringa oleifera Lam.) extract on the reduction in bacterial contaminants during spermatophore preservation due to the uncertainty of the broodstock. Spermatophores were suspended in five extenders: mineral oil, Ringer's solution, phosphate buffer, calcium‐free saline and 0.8% NaCl and stored at 2–4°C. During a 28‐day storage, spermatophores stored in mineral oil showed the highest sperm viability (89.1%) and intact morphology with a slight formation of hardened adhesive matrices. The effect of moringa extract was investigated on chilled spermatophores. Spermatophores were suspended in mineral oil (the control) and mineral oil containing either penicillin–streptomycin (0.1%) or moringa extract (0.1 mg/ml) during a 28‐day storage. Supplementation of moringa extract resulted in a significant increase (p < .05) in sperm survival, compared to the control, and a complete elimination of culturable Vibrio (Vibrio alginolyticus, Vibrio mimicus and Vibrio furnissii), Staphylococcus kloosii, Bacillus macerans, Listeria ivanovii, Corynebacterium paurometabolum and Corynebacterium bovis, in chilled spermatophores. Chilled storage of spermatophores in mineral oil containing moringa extract was a promising technique due to the inhibition of shrimp and human pathogens without the spermicidal effect on banana shrimp sperm.     

Effects of dietary mono‐ and multiprobiotic strains on growth performance,gut bacteria and body composition of Javanese carp (Puntius gonionotus,Bleeker 1850)

This study investigated the effects of dietary mono‐ and multiprobiotic strains of Enterococcus faecalis, Lactobacillus fermentum and Leuconostoc mesenteroides on growth performance, intestinal bacteria and body composition of Javanese carp (Puntius gonionotus). Moreover, the effect of storage temperature on lactic acid bacteria (LAB) viability in the feed was studied. Compared to the control group, significant (P < 0.05) effect on weight gain, feed conversion ratio, specific growth rate and protein efficiency ratio of probiotic fed Javanese carp was observed. Inclusion of individual LAB strains in the diet resulted in significantly improved growth performances of Javanese carps compared to fish fed a diet supplemented LAB mixture. The inclusion level of E. faecalis at 10⁷ colony‐forming unit (cfu) g⁻¹ in the diet revealed higher growth performance compared to other treatments. The population levels of LAB in the fish intestine were significantly increased while the levels of Gram‐negative bacteria were significantly decreased compared to the control. No significant variations were observed in the chemical composition of the carcass by probiotics. The viability of LAB in feed was higher when stored at 4 °C compared to 25 °C. It is suggested that E. faecalis has a greater potential for use in improving Javanese carp culture outcomes.     

Characterization of the testicular semen of the African catfish, Clarias gariepinus (Burchell, 1822), and its short-term storage

Semen of the African catfish, Clarias gariepinus (Burchell, 1822), was investigated with respect to its cellular composition, sperm cell density, maturation grade, motility and fertility. Storage conditions were tested, whereby sperm viability was assessed by measurement of the motility after activation and by fertility tests. Testicular semen differed in its composition, i.e. the sperm density and numbers of spermatids, according to the maturity grade of the testis. Two semen types could be distinguished: semen type I was characterized by high sperm densities and low numbers of spermatids and semen type II had lower sperm densities and higher numbers of spermatids. Two semen types did not differ in motility and fertility (when adjusted for differences in sperm density). During storage, the sperm viability was influenced by the sodium concentration of the storage medium, temperature, membrane stabilizers as bovine serum albumen (BSA) or hen egg yolk, antibiotics and oxygen. Semen viability was maintained best when it was diluted at a ratio of 1:5 in storage solution (150 mmol L^?1 NaCl, 2.5 mmol L^?1 KCl, 1 mmol L^?1 CaCl₂, 1 mmol L^?1 MgSO₄, 20 mmol L^?1 Tris (pH 8.5) and 0.5% BSA or 0.5% hen egg yolk) and stored at 4 °C. Oxygen gassing and addition of antibiotics (1 mg mL^?1 gentamycine sulphate) to the storage solution affected the two semen types in different ways. Antibiotics had no effect on type I semen, but had a positive effect on type II semen. Oxygen gassing had a positive effect on type I semen but a negative effect on type II semen.     

Preservation of Black Tiger Shrimp Penaeus monodon Spermatophores by Chilled Storage

Chilled storage of spermatozoa in fish has been extensively investigated for many years, but limited research was focused on crustacean species. Chilled storage of spermatophores of black tiger shrimp Penaeus monodon is needed to generate consistent and reliable supply of spermatozoa for subsequent use. The objective of this study was to develop a protocol for the chilled storage of black tiger shrimp spermatophores and to evaluate bacterial propagation during chilled storage of spermatophores. In the first experiment, spermatophores were selected and preserved using four different extenders, namely mineral oil, Ringer's solution, phosphate buffer and 0.85% sodium chloride, and stored at low temperature (2‐4 C) for 42 d without antibiotic supplementation. Results showed that mineral oil was the best extender for chilled storage of spermatophores, since the highest percentage of viable sperm (58.3 ± 2.9%) was observed with this extender at the end of experiment (day 42). Bacillus sp., Staphylococcus sp., and Pseudomonas aeruginosa were identified as the predominant bacteria occurring during chilled storage, and the total bacteria count gradually increased during the experiment. In the second experiment, spermatophores were preserved in the mineral oil with four concentrations of the antibiotic, penicillin‐streptomycin (0.1%,1%, 2%, and 3%). There was no significant difference (P 0.05) in the percentage of viable sperm among treatments with 0.1%,1 %, 2%, and 3% antibiotics. The total count of Bacillus sp., Staphylococcus sp., and P. aeruginosa in the antibiotic treated groups significantly decreased (P < 0.05) to undetectable levels by day 14 of the experiment. Fertility studies from artificial insemination indicated that P. monodon spermatophores preserved with mineral oil for 7‐8 d at 2‐4 C were capable of fertilizing eggs with hatching rates similar to the controls. This study suggests that chilled storage of spermatophores is a feasible approach for the management and spawning of black tiger prawn broodstock or other Invertebrate species that produce spermatophores.     

Effect of temperature on short-term storage of eggs and sperm of chum salmon (Oncorhynchus keta)

Chum salmon (Oncorhynchus keta) gametes were stored separately for intervals up to 460 h at temperatures ranging from 3 to 15°C. Estimates of time to 90 and 50% fertilization success (FS) were obtained for either stored eggs, stored milt, or stored eggs and milt. When both gametes were stored, the combined loss of gamete viability resulted in shorter times to 90 and 50% FS than when either eggs or milt were stored alone. Gamete storage at colder temperatures significantly prolonged viability; for example, when both gametes were stored, the time to 90% FS ranged from 19.6 h (15°C) to 123.9 h (3°C). Loss of viability of stored gametes in these trials was similar to that found in other studies with Oncorhynchus species at low storage temperatures (3–6°C), but gametes showed significantly greater viability when stored at higher temperatures (9–15°C). This increased viability in the current study appears to have resulted from the provision of (1) higher air-to-gamete ratios, and (2) greater interface area between air and gametes in the storage containers, two factors that would enhance gamete respiration during storage.     

Effect of microalgae and temperature on absorption efficiency of razor clam (Sinonovacula constricta Lamark, 1818)

The razor clam (Sinonovacula constricta) is a bivalve species living in the lower to mid intertidal zones along the coasts of China, Japan and Korea. In this study, the effects of temperature, microalgae species and concentration on the absorption efficiency (AE) of cultured adult S Constricta fed with six species of microalgae, including Chlorella sp., Pavlova viridis, Nitzschia closterium f. minutissima, Platymonas subcordiformis, Nannochloropsis oculata and Isochrysis zhanjiangensis was examined. The clams were exposed to three different temperatures (15, 20 and 25°C) and five microalgae concentrations (0.16, 0.27, 0.37, 0.45 and 0.53 mg L^?1). The results indicated that under different temperatures, there is significant difference (P < 0.05) in AE and the efficiency peaks at the water temperature of 20°C. Under different microalgae concentrations, the absorption efficiencies were also significantly different (P < 0.05) and there was a negative correlation between AE and microalgae concentration. At different combinations of temperature and microalgae concentration, the absorption efficiencies of Chlorella sp. and N. oculata were lower than those of other microalgae. The interaction of temperature and microalgae concentration affected the AE significantly (P < 0.05).     

Effect of the addition of diatoms (Navicula spp.) and rotifers (Brachionus plicatilis) on water quality and growth of the Litopenaeus vannamei postlarvae reared in a biofloc system

The aim of this study was to evaluate the effect of the addition of Navicula spp. and Brachionus plicatilis on water quality and growth of postlarvae shrimp Litopenaeus vannamei reared in a biofloc system. Four treatments were considered: a control (biofloc system – BFT); BFT with the addition of Navicula spp. (BFT‐N); BFT with the addition of Brachionus plicatilis (BFT‐B) and BFT with the addition of Navicula spp. and Brachionus plicatilis (BFT‐NB), each in triplicate. Shrimp (16.2 ± 0.03 mg) were stocked at a density of 2500 shrimp m^?3 and plankton were added on days 1, 5, 10, 15, 20, 25 and 30 at a density of 5 × 10⁴ cells mL^?1 (Navicula spp.) and 30 organisms L^?1 (Brachionus plicatilis). The shrimp were fed a formulated feed in four daily rations composed of 40% crude protein and 8% lipids. Significant differences between treatments were observed for final weight, yield, feed conversion ratio, specific growth rate, protein efficiency ratio and protein content of the shrimp. The combined plankton addition of Navicula spp. and B. plicatilis had better performance parameters, indicating their benefit as natural food sources for postlarvae L. vannamei in biofloc systems.     

Production of transparent exopolymer particles by four diatom species

The production of transparent exopolymer particles (TEP) by four diatoms, Coscinodiscus granii, Eucampia zodiacus, Rhizosolenia setigera, and Skeletonema sp., was examined. Most of the TEP in C. granii (74% of the maximum) were produced during the growth phase. In contrast, most of the TEP in E. zodiacus (73%), R. setigera (74%), and Skeletonema sp. (70%) were produced during the stationary and declining phases. The C. granii TEP production rate was highest in the growth phase, whereas those in E. zodiacus, R. setigera, and Skeletonema sp. were highest in the stationary–decline phase. The TEP concentrations per cell and the cell volume of C. granii were 34.97 ± 4.114 (mean ± SD) ng Xeq./cell (xanthan gum equivalents per cell) and 341.6 ± 56.33 fg Xeq./μm³, and were 23.01 and 4.32 times higher than the values obtained from the other three diatoms, respectively. The results suggest that the mechanisms of TEP production differ with growth stage and diatom species. Therefore, it is likely that the differences in TEP production among the diatom species influence the complexity of TEP dynamics in aquatic environments.     

Growth and potential purification ability of Nitzschia sp. benthic diatoms in sea cucumber aquaculture wastewater

The growth patterns and water treatment capacity of Nitzschia sp. benthic diatoms in different concentrations of sea cucumber aquaculture wastewater (0%, 10%, 30%, 50%, 80% and 100%) and f/2 medium were studied. Nitzschia sp. grew in different concentrations of aquaculture wastewater and showed remarkable differences in their rate of growth among the treatment groups. Nitzschia sp. grew most quickly (0.83 ind/day) and showed the greatest total chlorophyll‐a content in 30% wastewater. The total chlorophyll‐a content and growth rate of Nitzschia sp. were strongly correlated (R² > 0.98). The total lipid (TL), total protein, exopolysaccharide (EPS) and intracellular polysaccharide (IPS) contents of the diatoms were highest in 100% wastewater and showed significant differences among the experimental groups (p < 0.05). Total nitrogen (TN), ammonium‐nitrogen (NH₄‐N) (AN), nitrate nitrogen (NO₃‐N) (NN), nitrite nitrogen (NO₂‐N) (NIN) and total phosphate (TP) contents were significantly reduced after cultivation. TN uptake peaked at 54.58% in 30% wastewater. AN uptake exceeded 95% in 30% wastewater and 100% wastewater. NN uptake peaked at 56.42% in 80% wastewater, whereas TP uptake ranged from 16.80% to 27.69%. These results suggest that Nitzschia sp. biomass can be enhanced via cultivation in low‐concentration (30%) wastewater, after which their cultivation may be continued in high‐concentration (100%) wastewater, increasing their nutritional value and aiding in the removal of surplus nitrogen and phosphorus in sea cucumber aquaculture wastewater. Application of Nitzschia sp. using the recirculating wastewater‐treatment methods described has the potential to reduce environmental harm caused by sea cucumber cultivation and thus achieve sustainable aquaculture.