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.     

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。     

Quality evaluation of indoor‐ and outdoor‐cultured sea cucumber (Apostichopus japonicus) seedlings: Insight from survival and immune performance in response to combined stress of hyperthermia and hyposalinity

The mass mortalities of sea cucumber Apostichpous japonicus have prevailed in northern China, mainly attributing to the emergence of extreme environmental conditions, that is hyperthermia and hyposalinity. The high‐quality sea cucumber seedlings appear to possess more robust resistance to adverse conditions. There are usually indoor‐ and outdoor‐cultured seedlings in industrial production of sea cucumbers. Although the outdoor‐cultured sea cucumbers are practically considered to be more strong and robust, the effective evaluation approach to distinguish these seedlings has been scarce. The current study compared survival and immune performances of indoor‐ and outdoor‐cultured A. japonicus under combined exogenous stressors, that is hyperthermia and hyposalinity. Results based on secondary stress induction revealed that the activities of immune enzymes and levels of catecholamines in body wall of outdoor‐cultured seedlings were prominently higher than those of indoor‐cultured seedlings recovered for 0–72 hr following sublethal stress (30°C and 25 psu of salinity). The opposite case occurred on immune enzymes in coelomic fluid of the two sources of seedlings except for myeloperoxidase. Importantly, the outdoor‐cultured seedlings, which were recovered for 72 hr after sublethal stress, exhibited a 93% of cumulative survival rate following 7 days of recovery after lethal stress (33°C and 20 psu of salinity), 27% higher than the indoor‐cultured seedlings. Collectively, the outdoor‐cultured A. japonicus seedlings showed more superior quality than the hatchery‐produced seedlings in terms of survival and immune performance. These findings provide practically useful information towards quality distinction of the indoor‐ and outdoor‐cultured sea cucumbers, which could benefit the aquaculture industry to obtain high‐quality seedlings.     

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.     

Sea cucumber habitat differentiation and site retention as determined by intraspecific stable isotope variation

Stable carbon and nitrogen isotope ratios (δ¹³C/δ¹⁵N) were assessed as a means to ascertain the recent in situ feeding history of the common New Zealand sea cucumber Australostichopus mollis in relation to nutrient enrichment from a longline green‐lipped mussel (Perna canaliculus) farm in Northern New Zealand. δ¹³C and δ¹⁵N isotopic signatures and the ratios of sea cucumbers sampled from within the impact footprint of the mussel farm were compared with those of sea cucumbers residing on adjacent natural reefs. Sea cucumbers from beneath mussel farming longlines had significantly different δ¹³C stable isotope signatures in comparison with sea cucumbers collected from neighbouring natural reef habitats. This difference supports the hypothesis that sea cucumbers in the same bay maintain distinctly different feeding histories, with those residing beneath mussel farming longlines deriving tissue carbon from sediment impacted by farming activities. This hypothesis is further supported by the finding that the isotope signature of sediment collected from beneath the mussel farm is consistent with the expectation that sea cucumbers were feeding on and consuming sediment enriched with bivalve waste (faeces and pseudo‐faeces). In contrast, the nitrogen stable isotope signature (δ¹⁵N) was found to be similar between sites for both sea cucumbers and assumed food sources. Both findings lend support to the viability of future sea cucumber/green‐lipped mussel farm polyculture systems. Sea cucumbers in different locations (mussel farm, natural reef) possessed distinctly different isotope signatures, suggesting that mixing of sea ranched sea cucumbers with natural reef populations would be negligible or non‐existent. Similarities between the isotope signatures in low metabolic tissue of sea cucumbers residing at the mussel farm site to that of mussel farm‐impacted sediment suggest that cucumbers beneath mussel farms appear to have high rates of retention at the farm site.     

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.     

Quantification of waste feed and fish faeces in sediments beneath yellowtail pens and possibility to reduce waste loading by co‐culturing with sea cucumbers: an isotopic study

To evaluate environmental impacts of yellowtail culture and to examine the efficiency of the sea cucumber Apostichopus japonicus in reduction of waste loading, surface sediments were sampled and A. japonicus were cultured at a yellowtail farm in Owase Bay, Japan. Waste feed‐ and faeces‐derived organic matter (WOM, FOM) in sedimentary organic matter (SOM) was estimated based on the δ¹³C and δ¹⁵N of the fish feed (?21.7‰, 9.2‰), yellowtail faeces (?20.6‰, 6.2‰) and SOM reference (?24.4‰, 4.4‰). Small WOM (0–22% in SOM) but substantial FOM (28–61%) loadings in the fish farm area and high sulphide concentrations in the sediments (1.0 mg g^?1) suggest that reduction in the fish stocks or mitigation of the faeces should be considered. A. japonicus juveniles were cultured in three cages deployed below a pen and growth was assessed after three different periods (62, 107, 181 days). A. japonicus grew well during the first 107 days (daily specific growth rate, 3.7%) and their survivorship was high (80–90%). Growth ceased after 107 days, probably due to fouling on the cages. The δ¹³C and δ¹⁵N of their hypothetical diet (–19.7‰, 5.5‰) were close to the FOM values, suggesting assimilation of FOM.     

Effects of dietary protein levels on the activity of the digestive enzyme of albino and normal Apostichopus japonicus (Selenka)

We evaluated the effects of different proportions of dietary protein (5%, 10%, 15%, 20%, 25% and 30% protein) on the activity of digestive enzymes of normal and albino Apostichopus japonicus. The experimental diets were fed for 60 days, the optimal conditions for digestive enzyme activity in sea cucumbers were studied. The optimal temperature for protease was 29.3°C and the optimal pH was 1.8. The optimal temperature for amylase was 34.3°C and the optimal pH was 6.7. The optimal temperature for cellulase was 56°C and the optimal pH was 5.9. The activity of intestinal protease increased at first and then decreased as the proportion of dietary protein increased, reaching the maximum when the proportion of protein was 19.7%. The activity of protease in the intestine of normal sea cucumber was significantly lower than that of albino sea cucumber, and the activity of amylase was significantly higher than that of albino sea cucumber. This study is expected to provide a basis for further explaining the ecological difference of albino and normal A. japonicus.     

Large‐scale mortality and limited expression of heat shock proteins of aestivating sea cucumbers Apostichopus japonicus after acute salinity decrease

This study deals with the mortality and related physiological responses of aestivating sea cucumber Apostichopus japonicus to acute salinity decrease. Aestivating and active sea cucumbers were exposed to a decrease in salinity (from 30 to 20 psu) at a rate of 2.5 psu every 6 h, and then maintained at 20 psu for 96 h. The mortality of aestivating sea cucumbers was ~30%, which was significantly higher than that of active sea cucumbers (~10%). This result indicated that sea cucumbers in aestivation were more susceptible to hypo‐salinity stress. To elucidate the underlying physiological mechanisms, the osmotic pressure in coelomic fluid and the levels of hsp70 and hsp90 mRNA in aestivating and active sea cucumbers were measured. No significant difference in osmoregulation was observed between the two groups. The osmotic pressure of coelomic fluid in both groups changed with decrease in ambient salinity. There were significant differences in the time course and magnitude of hsp70 and hsp90 expression between the two groups. After exposure to decreased salinity, aestivating sea cucumbers showed a delayed up‐regulation of hsp70 and hsp90 expression compared with animals in active state, and these levels decreased rapidly to control values. The expression of hsp70 and hsp90 in aestivating sea cucumbers were significantly lower than those in active sea cucumbers after salinity change. The differences in hsp70 and hsp90 expression between the states may partly explain the higher mortality of sea cucumbers in aestivation when exposed to low salinity.     

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.     

Effect of replacing dietary fish meal with silkworm (Bombyx mori L) caterpillar meal on growth and non‐specific immunity of sea cucumber Apostichopus japonicus (Selenka)

The effect of dietary substitution of silkworm (Bombyx mori L) meal (SM) for fishmeal (FM) on the growth performance and non‐specific immunity of sea cucumber (Apostichopus japonicus) (initial weight: 12.8 ± 0.16 g) was determined. Four isonitrogenous and isocaloric diets were formulated: Diet 1, which served as the control diet, contained 5% FM; Diet 2 contained 3.75% FM and 1.25% SM; Diet 3 contained 2.5% FM and 2.5% SM; and Diet 4 contained 5% SM. Other ingredients in each of the four diets were kept in the same proportion. After 8 weeks of feeding, the results showed that sea cucumbers fed Diet 2 had 18.7% increases in weight over those fed the control diet, but no significant difference was observed. No obvious difference in body wall composition was detected among the sea cucumbers fed the four different diets. Immunity analysis indicated that phagocytosis and serum alkaline phosphatase activity were not significantly (P > 0.05) affected when FM was partially or completely replaced with SM. Serum lysozyme activity of sea cucumbers fed Diet 4 showed a significant (P < 0.05) growth increase compared with those fed control diet. The results revealed that SM could be an effective substitute for FM in sea cucumber diet.     

Suspended culture of the sea cucumber Apostichopus japonicus below a Pacific oyster raft – potential for integrated multi‐trophic aquaculture

To discuss the possibility of co‐culturing Pacific oyster with the sea cucumber Apostichopus japonicus, a field experiment was conducted in an oyster farm. Apostichopus japonicus juveniles (mean wet weight, 0.08 g) were cultured below an oyster raft and at a control station for 216 days, and the wet weight and stable isotope ratios (δ¹³C, δ¹⁵N) were analysed together with settling organic matter (OM) collected using sediment traps. All sea cucumbers cultured below the raft survived (survival rate, 100%), while at the control station one individual disappeared (96%). During 216 days, the juveniles at the oyster and control stations grew to a mean weight of 5.5 and 2.6 g, attaining respective specific growth rates of 2.0% and 1.6% (paired t‐test, P < 0.001). Settlement rates of carbon and nitrogen at the oyster station were ~5 times larger than those at the control station. The stable isotope analysis showed that settling OM at both stations originated from coastal phytoplankton and that phytoplankton represented the primary food source for A. japonicus. The rapid growth of A. japonicus at the oyster station was concluded to be due to the abundant supply of oyster biodeposits, which could be ingested by this species.     

Effects of differently processed diets on growth,immunity and water quality of the sea cucumber,Apostichopus japonicus (Selenka, 1867)

The type of formulated diet used in aquaculture systems affects the feed efficiency and water quality. In this study, the water quality, growth performance and immunity of the sea cucumber, Apostichopus japonicus (Selenka, 1867), fed diets produced using four different processing methods (extruded pellet diet, cold‐bonded pellet diet, flake diet and mash diet) were quantified for 60 days to identify the optimal feed type for culturing of this species. Sea cucumbers grew faster, the feed conversion ratio was much lower, and immunity indicators were higher when fed the extruded pellet diet compared to the other diets. Sea cucumbers fed the extruded pellet diet had the highest specific growth rate (0.96), whereas A. japonicus fed the cold‐bonded pellet diet had the lowest specific growth rate (0.51). The lysozyme activity of sea cucumbers fed the extruded pellet diet was higher (57.52) than that of A. japonicus fed the cold‐bonded pellet diet (39.22), flake diet (37.32) and mash diet (32.68). When animals were fed the mash diet, the ammonia–nitrogen, nitrite–nitrogen and phosphate productions were higher than in animals fed the other diets. These results indicate that the extruded pellet diet is the optimum feed type for use in the culture of A. japonicus.     

Effects of mud substrate and water current on the behavioral characteristics and growth of the sea cucumber Apostichopus japonicus in the Yuehu lagoon of northern China

To determine whether marine mud substrate is suitable for sea cucumber aquaculture, we studied the effects of sea mud on the behavioral characteristics, growth and survival of Apostichopus japonicus, in both the field and laboratory. Our results showed that sea mud is beneficial for the growth of A. japonicus, but was unfavorable for its locomotion and attachment when a water current was present. In the field experiment in Yuehu lagoon, juvenile A. japonicus preferred to inhabit the base of seaweeds or dead leaves, which provide a favorable substrate for both their locomotion and ingestion. The mud substrate was not suitable for the small juveniles to inhabit; therefore, >3.25 g ind^?1 is the preferred size for bottom-sowing culture of sea cucumbers on the seabed in a field environment such as the Yuehu lagoon. Water current is a key factor influencing sea cucumber distribution on the bare mud substrate, with 90 % of juvenile sea cucumbers (<40 g ind^?1) being unable to keep still in a current speed of 0.115 m s^?1 for 10 min. In conclusion, a mud substrate is suitable for A. japonicus aquaculture, although hard substrates or shelters are a prerequisite for successful rearing. The water current is a key factor that influences substrate selection by A. japonicus and, thus, is an important factor to be considered in the bottom-sowing culture of these organisms.     

玉足海参与凡纳滨对虾的混养效果

在室内条件下进行了玉足海参与凡纳滨对虾的混养实验,分析了单养与混养两种条件下养殖水体营养盐结构以及底质成分的变化,测定了对虾与海参的存活率与生长性能。结果显示,混养海参可以明显改变养殖系统的营养盐结构,可使水体中的磷酸盐和硝酸盐浓度有所升高,同时也可有效地控制系统中氨氮浓度。混养海参也可以大幅度地降低沉积物中有机质和硫化物含量,实验结束时混养组硫化物含量为(7.71±1.33)mg/kg,仅相当于单养组浓度的1/3。混养海参对对虾生长及存活具有明显的促进作用,其中混养组对虾体长特异增长率为(0.69±0.13)%/d,显著优于单养组(0.45±0.06)%/d;混养组对虾成活率可达72.5%±22.9%,显著高于对照组55.0%±17.5%。在混养系统内,对虾不会对海参的生存造成负面影响,海参能够有效地选择摄食和利用沉积物中的营养物质(对食物中有机质的同化率可达36.36%±13.79%),并以较快的速度生长。结果表明,在对虾养殖系统中混养玉足海参具有明显的环境与经济效益。本研究可为我国海水养殖业的可持续发展提供一定的科学依据。     

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.     

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.     

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.     

Optimum dietary protein level for growth and coelomic fluid non‐specific immune enzymes of sea cucumber Apostichopus japonicus juvenile

A feeding trial was conducted to determine the optimum dietary protein level of sea cucumber Apostichopus japonicus juvenile focusing on growth performance and non‐specific immune response. Diets with seven crude protein levels (42.0, 108.9, 155.2, 216.7, 258.0, 313.3 and 357.5 g kg^?1) were fed to sea cucumber juveniles (1.05 ±0.01 g) once a day for 100 days. More than 70% survival was observed, and there was no significant difference among all treatments. The sea cucumbers fed diets containing 108.9 g kg^?1 crude protein showed significantly (P < 0.05) higher body weight gain than those of the sea cucumbers fed diets containing 42.0, 216.7, 258.0, 313.3 and 357.5 g kg^?1 crude protein. No significantly differences (P > 0.05) were observed in moisture, crude protein, crude lipid, ash and carbohydrate content of the body wall among all treatments. The coelomic fluid catalase activity of the sea cucumbers generally increased with increasing dietary protein levels. Therefore, the acid phosphatase, superoxide dismutase and lysozyme activity increased with increasing dietary protein levels at first and decreased subsequently. The relationship between dietary protein levels and body weight gain was analysed by a second‐order polynomial regression analysis model. The result indicates that the optimum dietary protein level for sea cucumber juveniles is 135.4 g kg^?1.     

Utilization of dietary carbohydrates by sea cucumber Apostichopus japonicus (Selenka) as indicated by carbon stable isotope analysis

Carbon stable isotopes were used as trophic markers to investigate the utilization of dietary terrestrial‐source carbohydrates by sea cucumber Apostichopus japonicus. Sea cucumbers were fed by five different types of diets with the ingredients containing Sargassum muticum either without starch or with one of the four starches including corn starch, sweet potato starch, tapioca starch and potato starch. After the 70‐day feeding trial, the carbon isotopic compositions of A. japonicus appeared to reflect those of corresponding dietary components. The average contribution of corn starch (22.0%) to the growth of A. japonicus was slightly higher than the expected contribution (20%). While the proportional contributions of sweet potato, tapioca and potato starches (6.0%, 7.0% and 4.0%, respectively) were all considerably lower relative to the expected contributions. These results indicated that A. japonicus could utilize corn starch more efficiently than sweet potato, tapioca or potato starch. Moreover, A. japonicus fed diet containing corn starch showed the highest specific growth rates which were significantly higher than those fed diets containing potato or tapioca starch. The results of the present study suggested that the corn starch could be used as dietary carbohydrate source in the artificial feeds for A. japonicus farming.