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.     

N and P budgets of Haliotis discus hanai,Apostichopus japonicas,and Sebastes schlegeli in a polyculture system

The viability of placing abalones (Haliotis discus hannai), sea cucumbers (Apostichopus japonicas) and rockfish (Sebastes schlegeli) in a polyculture system, the effect of this mixed species group on the system's nitrogen (N) and phosphorous (P) budgets, and the growth and food intake of the organisms in the system were examined using a recirculating aquaculture system. Four replicates were set up for each of three treatment groups (abalone only (C), abalone‐sea cucumber (AS) and abalone‐sea cucumber‐rockfish (ASF)) with an experimental period of 60 d. Compared with the C group, in the AS group the abalone survival rate and specific growth rate (SGR) of body weight increased and the harvested abalones from the polyculture system became the main source of N and P output of the polyculture system. However, the N and P output in the water layer did not differ significantly from that in the C group (p > 0.05), and the N utilization rate was significantly higher than that in the C and ASF groups (p < 0.05). Compared with the AS group, in the ASF treatment the SGR of body weight as well as the protease and amylase activities of sea cucumbers were significantly higher (p < 0.05), the water layer and faeces became the main sources of N and P output in the system. These results showed that the AS polyculture mode significantly improved the N and P utilization rates in the system and led to increased aquaculture production.     

亚硒酸钠对刺参免疫反应中体腔液酶活力的影响

为了合理评价硒对水产养殖刺参的作用,实验检测和观察了室内模拟亚硒酸钠处理及病菌感染条件下刺参体腔液免疫酶的变化、组织病理变化和相对保护率。结果表明,随着亚硒酸钠处理强度的增加,刺参体腔液中超氧物岐化酶(SOD)、谷胱甘肽过氧化物酶(GP-X)、溶菌酶(LYZ)、酚氧化酶(PO)及碱性磷酸酶(ALP)活性升高;在同时感染病菌的情况下,SOD、GP-X及LYZ活性表现为先升高后下降的趋势,PO和ALP活性则持续上升,但随亚硒酸钠浓度升高,ALP活性增加的幅度减少,而较高亚硒酸钠浓度时累计发病率上升,相对保护率下降。研究结果表明,适宜浓度的亚硒酸钠可增强刺参对病菌感染的免疫力,而病菌感染可以加剧亚硒酸钠胁迫对刺参造成的免疫功能损伤,所以适度利用硒可减轻刺参养殖病害的发生。     

Feasibility of Offshore Co‐culture of Abalone,Haliotis discus hannai Ino,and Sea Cucumber,Apostichopus japonicus,in a Temperate Zone

Feasibility of offshore co‐culture of abalone and sea cucumber was investigated in Northern China. Survival and growth of abalone, Haliotis discus hannai Ino, and sea cucumber, Apostichopus japonicus, co‐cultured in abalone cages from suspended longlines, in the offshore area, were examined. Abalone and sea cucumbers were co‐cultured at density ratios of both 3:1 and 6:1 for 1 yr. Abalone were fed with fresh kelp and no additional feed was given to sea cucumbers. Survival of abalone and sea cucumber was 100% for all treatments. Abalone and sea cucumber grew well; the body weight (BW) of abalone and sea cucumber was nearly doubled and had reached a commercial size. There were no significant differences in the growth rates for both abalone and sea cucumber between the two density treatments. The specific growth rate of BW of abalone (SGRbw) was highest in June, with a value of 0.536%/d. Growth rate of sea cucumber (SGRsc) was highest in December, reached 1.84%/d, with an annual average SGRsc of 0.182%/d. Results suggested that the offshore co‐culture of abalone and sea cucumber was feasible offshore. The co‐culture of abalone with sea cucumbers may provide an additional valuable crop without additional financial input.     

Co‐culture of sea cucumber Holothuria scabra and red seaweed Kappaphycus striatum

Commercially valuable sea cucumbers are potential co‐culture species in tropical lagoon environments, where they may be integrated into established aquaculture areas used for seaweed farming. In the current study, wild‐caught juvenile sea cucumbers, Holothuria scabra, and red seaweed Kappaphycus striatum were co‐cultured on Zanzibar, United Republic of Tanzania. Sea cucumbers (97 g ± 31 SD, n = 52) were cultured in mesh enclosures at initial cage stocking densities of 124 ± 21 SD and 218 ± 16 SD g m^?2 under seaweed culture lines. Over 83 days, individual growth rate (1.6 g d^?1 ± 0.2 SD) of sea cucumbers at low stocking density was significantly higher (χ² = 8.292, d.f. = 1, P = 0.004) than at high‐stocking density (0.9 g d^?1 ± 0.1 SD). Seaweed individual growth rates [6.27 (±0.3 SE) g d^?1] were highest in co‐culture with sea cucumber at low density but did not differ significantly from high sea cucumber density or seaweed monoculture treatments (χ² = 3.0885, d.f. = 2, P = 0.2135). Seaweed growth varied significantly (χ² = 35.6, d.f. = 2, P < 0.0001) with sampling period, with the final sampling period resulting in the highest growth rate. Growth performance for seaweed and sea cucumbers (χ² = 3.089, d.f. = 2, P = 0.21 and χ² = 0.08, d.f. = 1, P = 0.777 respectively), did not differ significantly between monoculture and co‐culture treatments, yet growth in co‐culture was comparable with that reported for existing commercial monoculture. Results indicate H. scabra is a highly viable candidate species for lagoon co‐culture with seaweed. Co‐culture offers a more efficient use of limited coastal space over monoculture and is recommended as a potential coastal livelihood option for lagoon farmers in tropical regions.     

Effects of kelp residues fermented with probiotics on the culture of sea cucumber,Apostichopus japonicus

The kelp aquaculture production in China is the largest in the world, and a large amount of kelp residue is produced by kelp processing. Kelp residues contain substantial quantities of crude fibre, protein, and residual alginic acid, and may be used as feedstuff for aquaculture animals. In this study, we used probiotics to ferment kelp residues to improve kelp nutrient content and then fed the fermented kelp to the sea cucumber, Apostichopus japonicus. To study the effect of fermented feed on sea cucumber, its growth performance, digestive enzyme activity, diversity of intestinal microbiota and water quality of the sea cucumber culture water were determined. Growth performance of sea cucumber fed with fermented feed significantly (p < .01) increased when compared with sea cucumber fed with formulated feed. Amylase, cellulose and alginase activities were significantly (p < .01) higher in the fermented feed group when compared with the formulated feed group. The total number and diversity of intestinal microbiota showed a significant increase in sea cucumbers fed with the fermented feed. The water quality of the fermented feed group showed much lower ammonia and nitrite (<0.050 mg/L) levels when compared with the formulated feed group. These results suggest that kelp residues fermented with probiotics enhance the growth, digestive enzyme activities and intestinal microbiota of sea cucumbers and improve the culture water quality. Fermented kelp residues are a new supplementary nutrient source for sea cucumbers and may be applicable to other animal aquacultures.     

Effects of salinity on ingestion,oxygen consumption and ammonium excretion rates of the sea cucumber Holothuria leucospilota

The sea cucumber Holothuria leucospilota is a good candidate for aquaculture, for large‐scale production of this sea cucumber, it is imperative to know the effects of salinity on its physiological performance. In this study, ingestion, oxygen consumption and ammonium excretion rates of the adult sea cucumber H.leucospilota (16.98 ± 1.14 g, wet weight) at various salinity levels (18, 23, 28, 33 and 38 PSU) were studied in the laboratory. The species were acclimated for 1 week at the desired salinity before testing, and were fed with sediment from their natural habitat during this period. Results showed that the minimum ingestion rate (0.02 ± 0.01 g g^?1d^?1) at a salinity of 18 PSU was significantly lower than those observed at salinities of 28, 33 and 38 PSU, and there was no significant difference among the values at 23, 28, 33 and 38 PSU. The maximum value of oxygen consumption rate recorded at a salinity of 28 PSU was significantly higher than the minimum at 18 PSU, no significant differences were observed among other treatments. The ammonium excretion rates of H. leucospilota also changed significantly in response to salinity variations, the maximum value observed at a salinity of 28 PSU (0.09 ± 0.03 μM g^?1h^?1) being nearly five times higher than the minimum value at a salinity of 38 PSU (0.02 ± 0.01 μM g^?1h^?1). The O:N ratio varied as a function of salinity. Lower O:N ratios (<11.0) at salinities below 23 PSU indicated protein‐dominated catabolism under hyposaline stress; the higher O:N ratio (46.5) at a salinity of 38 PSU indicated carbon‐based metabolism. Results of this study indicated that the sea cucumber H. leucospilota may have a wide tolerance of salinity variation. However, it is not a very suitable species for rearing in hyposaline water. This study provides useful information for improving aquaculture management in tropical and subtropical coastal areas.     

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.     

The role of polychaete Nereis diversicolor in bioremediation of wastewater and its growth performance and fatty acid composition in an integrated culture system with Huso huso (Linnaeus, 1758)

This study was undertaken to evaluate the role of polychaete Nereis diversicolor in bioremediation of waste water and its growth performance and fatty acid composition in an integrated culture system with great sturgeon, Huso huso. Three treatments consisting of N. diversicolor fed with H. huso waste (FNW), N. diversicolor fed with fish feed waste (NW), and fish waste without the worm (FW) were considered at water temperature of 23°C for 8 weeks. The obtained results demonstrated that N. diversicolor in the flow‐through system could grow via feeding with the fish waste water. The pure production and survival rate of harvested Nereis in NW treatment were significantly higher than those of FNW treatment (p < .05). However, no significant difference was observed in specific growth rate and weight gain between these two treatments (p > .05). The highest removal efficiency of waste water including total nitrogen (56%), total phosphorus (53%), NO₂‐N (91%), NH₃‐N (35%)_, PO₄‐P (47%), BOD₅ (60%) were seen in FNW treatment. Also, the highest additional efficiency of NO₃‐N occurred in FW (37%) treatment. Certain fatty acids specifically 20:5 ω3 (eicosapentaenoic acid [EPA]) and 22:6 ω6 (docosahexaenoic acid [DHA]) were also abundant in Nereis, and analysis revealed some differences due to the diet. These results demonstrated that the promotion of growth by cultured Nereis can enhance the decomposition rate of organic matter in enriched sediment and minimize negative effects in fish farms. These results also suggest that the use of N. diversicolor is an excellent potential candidate for an integrated aquaculture and nutrient recycling including the removal of organic wastes.     

A preliminary study on the potential value of a novel integrated aquaculture system on water purification

Intensive and semi-intensive sea cucumber aquaculture produces effluents that impact the quality of the local aquatic environment and sea cucumber growth; such effluents are an important cause of coastal water eutrophication. Integrated aquaculture has been shown to efficiently reduce the release of nutrients during aquaculture and to provide economic benefits. In this study, we report our investigation of a polyculture system utilizing Styela clava (stalked sea squirt) and Stichopus japonicus (Japanese sea cucumber) under two feeding modes. To examine purification of the water in the system, nutrients in the water and the sediment, attached heterotrophic bacteria, and the survival rates and growth rates of S. clava and S. japonicus were determined. Tank cultivation trials showed that, under the same feeding modes, the concentration of nutrients in the polyculture system was approximately 50–60 % of the sum of the nutrients in the S. japonicus mixture and S. clava monoculture systems. The abundance of attached heterotrophic bacteria in the polyculture system was remarkably lower than that of the mixed culture system under the same feeding mode. S. japonicus in the polyculture system grew better than those in the mixed culture system under the same feeding mode. These results demonstrate that the S. clava–S. japonicus integrated culture system offers a means of constraining or reversing the pollutive impacts of coastal sea cucumber aquaculture.     

Nitrogen and phosphorus budget of a Haliotis discus hannai and Apostichopus japonicus polyculture system

The system nitrogen (N), phosphorous (P) budget, N/P utilization rate and the physiological response mechanism of the abalone Haliotis discus hannai (body weight: 12.87 ± 0.82 g) and the sea cucumber Apostichopus japonicus (body weight: 10.85 ± 1.16 g) to different co‐culture environment conditions were examined. Animals were kept in a multilayer, cubic recirculating aquaculture system at different polyculture densities (abalones at 400 ind/m²in monoculture [Group C] and abalones at 400 ind/m²with sea cucumbers at 10 ind/m² [AS1] or 20 ind/m² [AS2]). Each treatment was replicated four times, and the experimental cycle was 90 days. No significant difference in survival rate of abalones was detected when the stocking density of sea cucumbers increased from 10 to 20 ind/m², but the concentrations of total ammonia nitrogen and nitrite nitrogen in the water were significantly higher in AS2 than in AS1. Survival rate, specific growth rate (SGR) of body weight of sea cucumbers and SGR of body weight of abalones were significantly lower in AS2 than in AS1. No significant difference in protease (PES), lipase, amylase and cellulase activities of abalones was identified between Group C and AS1, but the PES and amylase activities of abalones and sea cucumbers in AS1 were significantly higher than those in AS2. In AS1, the N/P output from harvesting of abalones and sea cucumbers and the N/P utilization rates were significantly higher than those in AS2. Although the N/P output from faeces was significantly lower in AS2 than in Group C and AS1, the N/P output from the water layer was significantly higher than that in AS1. The expression levels of Cu/Zn superoxide dismutase (Cu/Zn‐SOD) and heat shock protein 70 (HSP70) of both abalones and sea cucumbers in AS2 were significantly higher than those in AS1. No significant difference in expression of catalase (CAT) and HSP90of abalones was identified among these groups, but the expression levels of CAT and HSP90of sea cucumbers in AS2 were significantly higher than those in AS1. These results indicate that stocking sea cucumbers at 10 ind/m² in the polyculture system will relieve the organic load on the system and improve the N/P utilization rate. It will also increase aquaculture production and improve the ecological and economic benefits of the system.     

山东省刺参养殖产业现状分析与可持续发展对策

对近几年迅猛发展起来的山东省刺参养殖产业状况进行了详细的调查研究与分析。山东省作为我国刺参养殖的主产地,初步构建了刺参养殖优势产业带。以烟台、威海、青岛等地区为原主产区的刺参养殖属刺参优势产业带,主导着行业的发展;东营、滨州二地市属开发引进刺参养殖新兴产业带,证明在我省西部部分沿海实施"东参西养"是可行的;以日照、莱州地区为主的深水井大棚工厂化养参属新模式开发优势产业带,成为2007年以来刺参养殖的新亮点。此外,本文系统总结了山东省刺参养殖产业发展所面临的问题与挑战,提出了发展对策,对山东省乃至我国刺参养殖业的健康可持续发展具有很好的指导意义,并为相关主管部门的决策导向提供了可靠的理论依据和技术支持。     

Comparison of bacterial communities in channel catfish Ictalurus punctatus culture ponds of an industrial ecological purification recirculating aquaculture system

The industrial aquaculture pond system has gradually replaced the use of traditional earthen pond, as it causes less pollution and is more economical. In this study, an industrial ecological purification recirculating aquaculture system consisting of the water source pond, high‐density culture ponds, a deposit pond, and ecological purification ponds for channel catfish cultivation was established. Twelve water samples from different ponds were sequenced, and the bacterial communities were analysed. The abundances of Cyanobacteria and Merismopedia varied in different functional ponds of the system. The water quality was stable after two months of cultivation at 1.89 ± 0.22 mg/L total nitrogen, 1.1 ± 0.08 mg/L NH₄‐N and 0.43 ± 0.1 mg/L total phosphorus. The fish weight increased in a nearly linear manner, reaching 237.63 ± 23.8 per fish at day 120. An analysis of the environmental parameters, water quality and fish weight suggested that the system had an effective water purification process. Canonical correspondence analysis showed that the community was affected at the genus and phylum levels by different environmental parameters. We identified several dominant beneficial bacteria with nutrient removal abilities. Overall, our results demonstrated that the ecological purification recirculating aquaculture system had notable effects on water quality improvement and promoted changes in bacterial populations. These results provide important information on the microbial ecology of pond industrial eco‐aquaculture systems.     

Effect of support medium,hydraulic loading rate and plant density on water quality and growth of halophytes in marine aquaponic systems

The development of marine intensive land‐based aquaculture systems has been limited due to the absence of methods to manage saline wastewater. Aquaponic systems, although commonly applied to freshwater aquaculture, can potentially manage nutrient wastes while providing a secondary product. The aim of this study was to evaluate both the capacity for water treatment and the production requirements of two saltwater‐tolerant plant species (Sesuvium portulacastrum and Batis maritima) when grown hydroponically in a marine aquaponic system. The presence of plants was found to significantly contribute to nitrate removal, such that mean nitrate concentrations were 10.1 ± 5.4 and 12.1 ± 6.1 mg/L NO₃^?‐N in planted and unplanted treatments respectively. The use of coconut fibre as a planting medium also significantly contributed to nitrate removal, such that mean nitrate concentrations were 9.78 ± 5.4 and 12.4 ± 6.0 mg/L NO₃^?‐N in coconut fibre and expanded clay treatments respectively. Daily nitrogen removal was greatest in the coconut fibre/plants treatment, ranging from ?18% to 67%. Hydraulic loading rate, plant species and plant density did not significantly affect water quality or plant growth. The low flow/saltwort/low density treatment had the greatest mean daily nitrogen removal, ranging from 25% to 172%. The results indicate that the main nitrogen removal mechanisms were simultaneous nitrification–denitrification in the hydroponic plant beds and nitrogen removal through plant growth. This study demonstrates that marine aquaponics could be an effective way to manage nutrient removal in marine land‐based aquaculture systems.     

An annual faecal 16S amplicon sequencing of individual sea cucumber (Apostichopus japonicus) demonstrates the feeding behaviours against eukaryotes in natural environments

To fill in the gaps in knowledge as to how individual sea cucumber Apostichopus japonicus behave consuming eukaryotic food sources in natural environments, eukaryotic communities in the faeces of sea cucumbers and sediments were analysed through one whole year based on 16S rRNA gene sequencing of the organelle genomes. A total of 390 eukaryotic features were obtained, and 99.7% of the features were assigned to chloroplasts. The eukaryotic communities in faeces and sediments showed seasonal fluctuations through one whole year based on Bray‐Curtis distance and community composition. Comparison of eukaryotic communities between faeces and sediments showed that 12 families including Chaetocerotaceae and Laminariaceae were more abundant in faeces than in sediments, suggesting that sea cucumbers may choose sediment containing these algal taxa more often compared with others in natural environments. All features of Laminariaceae were assigned to Saccharina japonica, which is consistent with the fact that this alga is one of the most suitable diets in the aquaculture of A. japonicus. Assessments of individual 16S amplicon sequences of both faecal and sediment samples could be an alternative tool to help us understand dynamic feeding behaviours of sea cucumber populations in contributing to bioresource conservation and development of a superior approach to aquaculture.     

Bottom culture of the sea cucumber Apostichopus japonicus Selenka (Echinodermata: Holothuroidea) in a fish farm,southern China

The bottom culture of southward‐transplanted sea cucumber Apostichopus japonicus in a subtropical fish farm was investigated in a field study at Dapeng Cove, Daya Bay, from January 5–August 5 2011, with the aim of finding the ideal period for culturing A. japonicus in fish farms, and developing an integrated multi‐trophic aquaculture (IMTA) in southern China. Results showed that the bottom‐cultured sea cucumbers survived well (100%) before summer, survival rates decreased to 65.00 ± 21.21% in July, and all animals had died at the end of the study. Specific growth rates of the sea cucumbers were high during winter (1.05 ± 0.03% d^?1), decreased in early spring (0.44 ± 0.11% d^?1) and became negative in the following months. Growth rate was mainly influenced by water temperature, dissolved oxygen and sulphide content; the anoxia caused by water column stratification at the seafloor in the summer were the main causes of mass mortality. Our results indicate that bottom culture in the temperate season (winter and spring, optimally from late November to early April) is a viable way to rear the deposit feeder A. japonicus underneath a subtropical fish farm.     

Breeding and larval development of Holothuria mammata,a new target species for aquaculture

Sea cucumber commercial fisheries in the North‐eastern Atlantic and Mediterranean Sea started in Turkey in the 1990s. Due to ineffective management practices, the sea cucumber resource was overexploited. Holothuria mammata is one of the sea cucumber species exploited from this geographical area, showing high potential for its aquaculture. This research was undertaken to develop the breeding, larval and juveniles rearing techniques for development of H. mammata aquaculture. Broodstocks collected from Ria Formosa (Faro, S Portugal) were successfully induced to spawn by thermal stimulation from July to October, yielding up to 6.95 million eggs/female. The eggs and larvae were reared and their development described. H. mammata showed the five typical larval stages of most aspidochirote holoturians. Juveniles stage was reached after 21 days post‐fertilization. This is the first work focused on the aquaculture biotechnology of H. mammata, however, further research is need to improve the survival of juveniles to ensure the future production of this species.     

Dietary protein level and C/N ratio manipulation in zero‐exchange culture of Litopenaeus vannamei: Evaluation of inorganic nitrogen control,biofloc composition and shrimp performance

A 30‐day experiment was conducted to evaluate inorganic nitrogen control, biofloc composition and shrimp performance in zero‐exchange culture tanks for juvenile L. vannamei offered a 35% (P35) or 25% (P25) crude protein feed, each feed supplemented with additional carbohydrate to increase the C/N ratio to 20:1 (CN20) or 15:1 (CN15). Sucrose was used as a carbohydrate to manipulate the two C/N ratios based on the carbon and nitrogen content of both the feeds and sucrose. The four treatments were referred to as: P35 + CN20, P35 + CN15, P25 + CN20 and P25 + CN15. Each treatment consisted of four replicate tanks (125 L), each stocked with 28 shrimp (equivalent to 224 shrimp m^?3). Bioflocs formed and developed based on initial inoculation in all four treatments; and monitored water quality parameters were maintained within acceptable ranges for shrimp culture throughout the experiment. No significant effects (P > 0.05) of dietary protein level, C/N ratio or their interaction were observed on biofloc development (BFV, TSS and BFVI) and inorganic nitrogen (TAN, NO₂^?‐N and NO₃^?‐N) concentrations. At the end of the experiment, proximate analysis of the bioflocs collected from the four treatments showed crude protein levels of 21.3% ~ 32.1%, crude lipid levels of 1.6% ~ 2.8% and ash levels of 43.4% ~ 61.4%. Extracellular protease and amylase activities of the bioflocs were 9.9 ~ 14.4 U g^?1 TSS and 293.5 ~ 403.8 U g^?1 TSS respectively. Biofloc composition and enzyme activity were both affected by dietary protein level (P < 0.01) and C/N ratio (P < 0.05). Survival, per cent weight gain and protein efficiency ratio of shrimp were not affected (P > 0.05) by dietary protein level, C/N ratio or their interaction; however, the feed conversion ratios were significantly lower (P < 0.05) in treatments with high dietary protein (P35) compared with those in treatments with low dietary protein (P25). The results from this study demonstrate that dietary protein level and C/N ratio manipulation can have important implications for water quality, biofloc composition and shrimp performance in intensive, zero‐exchange biofloc‐based culture systems.     

Survival and growth of the sea cucumber Holothuria leucospilota Brandt: a comparison between suspended and bottom cultures in a subtropical fish farm during summer

The feasibility of co‐culturing the sea cucumber Holothuria leucospilota Brandt in a subtropical fish farm was investigated in a field study. Sea cucumbers were cultured in the fish farm in cages suspended at 4 m deep (suspended culture) and directly on the seafloor (bottom culture). The survival and growth of the sea cucumbers were monitored twice during the 3‐month, summer experimental period (May 26–August 14, 2010). Results showed that the suspension‐cultured sea cucumbers exhibited excellent survival rate (100%) during the whole study period. There also occurred no mortality in the bottom‐cultured sea cucumbers during the first culture period (May 26–July 13); but all these died from anoxia caused by water column stratification during the second culture period (July 14–August 14). The specific growth rate of the bottom‐cultured sea cucumbers (1.05 ± 0.21 % day^?1) was nearly double that of the suspended culture animals (0.57 ± 0.21 % day^?1) during the first culture period, and the growth rates of the suspended culture sea cucumbers in the second culture periods (0.46 ± 0.24 % day^?1) was only a little lower than that of the first period. The sea cucumbers H. leucospilota could ingest and assimilate sediment with high organic matter content with an average assimilation efficiency of 14.9 ± 3.9%. This study indicated that fish farm detritus can be effectively used as a food source for the sea cucumber and that it can be turned into a valuable secondary crop in the form of the sea cucumber biomass.     

Total organic carbon budget of integrated aquaculture system of sea cucumber Apostichopus japonicus,jellyfish Rhopilema esculenta and shrimp Fenneropenaeus chinensis

The total organic carbon (TOC) budget of the integrated aquaculture system of sea cucumber Apostichopus japonicus, jellyfish Rhopilema esculenta and shrimp Fenneropenaeus chinensis was investigated in a cofferdam (1.202 km²) for 13‐month field study. The results showed that the total input of TOC to the system was 498 300 kg year^?1, of which photosynthesis accounted for 26.8% of input TOC. The TOC production of the sea cucumber was 3668 kg year^?1, and that of the jellyfish and the shrimp was 714 kg year^?1. The TOC utilization rate of the input TOC by sea cucumber production was 7.4‰, and that of the integrated system increased by 18.9% than that of sea cucumber monoculture model through integration with jellyfish and shrimp. The outflow TOC from the system was 336 600 kg year^?1, which account for 92.7% of the inflow TOC. The integrated aquaculture system not only produce aquatic products, but also eliminate 7.3% of the inflow TOC, therefore, this system was not only a production system of aquatic products, but also an organic matter purification system for the coastal environment. The TOC utilization rate of the system can be probably improved by means of increasing stocking density of the sea cucumber and/or the shrimp.