Combined effects of acute thermal and hypo-osmotic stresses on osmolality and hsp70, hsp90 and sod expression in the sea cucumber Apostichopus japonicus Selenka

The combined effects of acute temperature and salinity on osmolality, expressions of heat shock proteins mRNA (hsp70, hsp90a and hsp90b) and superoxide dismutase mRNA (sod) were investigated in the sea cucumber Apostichopus japonicus Selenka. There were 12 treatments (combinations of temperature at 16, 20, 24 and 28 °C and salinity at 22, 27 and 32 ppt). In low salinity environments, the osmolality of the sea cucumber’s coelomic fluid decreased immediately and reached osmotic balance within 6 h. The decline of osmolality after 2 h of hypo-osmotic stress was faster at high temperatures (28 °C) than that at low temperatures (16 and 20 °C). Cellular level stress was indicated by up-regulation of hsp70, hsp90s and sod mRNA, and the maximal expression of all genes occurred at 6 h after stresses. The up-regulation of hsps and sod mRNA indicated the emergence of protein denaturation and oxidative damage and also suggested an increase in energy consumption at high temperature and low salinity. These results indicated that high temperature and low salinity could change biochemical pathways and energy budgets and then potentially impair the osmoregulation of the sea cucumber. Therefore, effective ways should be taken (e.g., draining off the upper freshwater, exchanging water and adding man-made sea water) to prevent the damage to sea cucumber culture caused by low salinity induced by rainstorms, especially at high temperature.     

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.     

Effects of body size and water temperature on food consumption and growth in the sea cucumber Apostichopus japonicus (Selenka) with special reference to aestivation

To investigate the effects of body size and water temperature on feeding and growth in the sea cucumber Apostichopus japonicus (Selenka), the maximum rate of food consumption in terms of energy (C_maxe; J day^?1) and the specific growth rate in terms of energy (SGRe; % day^?1) in animals of three body sizes (mean±SE) – large (134.0±3.5 g), medium (73.6±2.2 g) and small (36.5±1.2 g) – were determined at water temperatures of 10, 15, 20, 25 and 30°C. Maximum rate of food consumption in terms of energy increased and SGRe decreased with increasing body weight at 10, 15 and 20°C. This trend, however, was not apparent at 25 and 30°C, which could be influenced by aestivation. High water temperatures (above 20°C) were disadvantageous to feeding and growth of this animal; SGRe of A. japonicus during aestivation was negative. The optimum temperatures for food consumption and for growth were similar and were between 14 and 15°C, and body size seemed to have a slight effect on the optimal temperature for food consumption or growth. Because aestivation of A. japonicus was temperature dependent, the present paper also documented the threshold temperatures to aestivation as indicated by feeding cessation. Deduced from daily food consumption of individuals, the threshold temperature to aestivation for large and medium animals (73.3–139.3 g) was 24.5?25.5°C, while that for small animals (28.9–40.7 g) was between 25.5 and 30.5°C. These values are higher than previous reports; differences in sign of aestivation, experimental condition and dwelling district of test animals could be the reasons.     

Effects of stocking density,temperature, and salinity on larval survival and growth of the red race of the sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis> (Selenka)

The red race of the sea cucumber Apostichopus japonicus was introduced into China from Japan for large-scale seed production because of its economic value. This paper reports the effects of stocking density, temperature, and salinity on survival and growth of early larvae before and after feeding, in order to establish conditions for optimal larval growth and production. To maximize the yield per unit of space, densities of 0.5–1 larvae/ml are recommended for non-feeding larvae, while 0.1–0.2 larvae/ml are best for feeding larvae. Higher survival and growth values were obtained for both non-feeding and feeding larvae at temperature ranges from 21 to 24°C. Larvae reared at a salinity of 30‰ always showed maximum growth and survival. Based on results of this study, a temperature range from 21 to 24°C and a salinity of 30 are considered optimal for early development of the red A. japonicus.     

Release size and stocking density for grow-out of <Emphasis Type="Italic">Apostichopus japonicus</Emphasis> in the sea with raft-cultured macroalgae

Sea cucumber, Apostichopus japonicus, is the main cultured species in China. The main culture style for this species is the sea ranching model. Field trials were conducted in bottom-cages to preliminary reveal optimal releasing size, as well as maximum density of A. japonicus in an integrated multi-trophic aquaculture sea ranching area. Different sizes (4–30 g ind^?1) and densities (336–1342 g m^?2) of sea cucumbers were cultured for 13 months in Rongcheng Bay, Shandong Province, China. The size experiment showed that sea cucumber of all sizes grew throughout the experimental period. Sea cucumbers <15 g had high mortality in summer and low SGR in winter, while larger individual (>20 g ind^?1) had no advantage of growth. Sea cucumber sizes of 15–20 g may be suitable for release, considering their higher survival rate and SGR. The density experiment showed that the high biomass group had a low SGR and that the maximum release biomass was 793 g m^?2 based on a regression analysis. The optimal practical release season for sea cucumber was spring based on the results of two field experiments.     

Effects of l‐tryptophan on the performance,energy partitioning and endocrine response of Japanese sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress

The effects of dietary tryptophan on growth performance, energy budget and endocrine response of sea cucumber Apostichopus japonicus (Selenka) were studied, to test whether the tryptophan could mitigate the crowding stress response of the sea cucumber. Four density treatments of the sea cucumber (i.e. 4, 8, 16 and 32 individuals per 40 L water, represented as L, ML, MH and H) were fed with diets containing 0 (control), 1%, 3% and 5% l ‐tryptophan, respectively, for 75 days. The results showed that the specific growth rate (SGR) and feed conversion ratio (FCE) of A. japonicus decreased with increasing in the stocking densities but increased after supplementation of 1% and 3% tryptophan. The energy allocation of the A. japonicus was affected significantly by stocking density and dietary tryptophan treatments (p < .05). In general, the energy consumed (C) and energy used for growth (G) decreased with the increasing in the stocking densities. The highest proportion of energy deposited to growth occurred in each 3% treatment (L, 6.38%; ML, 6.12%; MH, 4.56% and H, 4.14%), which were significantly higher than the controls (p < .05) respectively. Higher cortisol, glucose and lactate levels of A. japonicus were recorded in the control treatments of MH and H, but l ‐tryptophan supplementation could reduce the levels of cortisol, glucose and lactate of the test animals. The present results proved that the growth performance of the sea cucumber was inhibited by high stocking densities, while dietary supplementation of tryptophan could significantly mitigate the crowding stress, and improve the growth of sea cucumber.     

Feeding physiology and scope for growth of the oyster Crassostrea corteziensis (Hertlein, 1951) acclimated to different conditions of temperature and salinity

There is a particular interest in Mexico for the grow-out and breeding in captivity of the native oyster Crassostrea corteziensis. However, there is a lack of knowledge of the effect of temperature and salinity on the feeding physiology that maximizes the growth and eventually achieves the maturation of C. corteziensis. Our aim was to evaluate the filtration and clearance rates, oxygen consumption, ammonium excretion rates, assimilation efficiency, and scope for growth of the oyster C. corteziensis acclimated during 2 weeks to different combinations of temperature (23, 26, 29, and 32 °C) and salinity (20, 30, 40, and 50 psu). Oysters were fed with a standard suspension of the microalga Chaetoceros muelleri as total particulate matter, which was supplied at 4.2 L h^?1 into 10 1-L tanks used as experimental chambers. The results showed that filtration and clearance rates increased with increasing temperature and decreased with increasing salinity, with the highest values obtained at 29 °C and 20 psu. Ammonium excretion and, to lesser extent, oxygen consumption matched with the variations in the feeding rate. The values of the scope for growth (SFG) suggested that C. corteziensis is able to grow out in all combinations of temperatures and salinities tested in this work. However, the SFG decreased at higher salinity (50 psu) in both extreme temperatures (23 and 32 °C), with highest value occurring at intermediate temperature and the lowest salinity. The SFG increased with increasing temperature and decreased with increasing salinity, which was explained by the increase in the feeding rates and ammonium excretion, coupled with higher absorption efficiency of the food. We concluded that higher filtrations and scope for growth of oysters occurred at 29 °C in brackish-water (20 psu) rather than in marine-water conditions. The results obtained can be considered highly useful information for aquacultural management of this oyster species, and useful to establish suitable sites to enhance their cultivation and maximize the growth of C. corteziensis.     

Effect of salinity on growth and energy budget of red and green colour variant sea cucumber Apostichopus japonicus (Selenca)

Sea cucumber, Apostichopus japonicus (Selenca), tolerates salinity fluctuations inhabiting intertide zone. This study deals with growth, food intake, food conversion and the bioenergetic responses of the red variant (wet weight of 2.60 ± 0.11g) and green variant (wet weight of 2.56 ± 0.08 g) A. japonicus to different salinities of 22, 26, 30, 34, and 38 psu at 16.5 ± 0.5°C. The results showed that salinity had a significant effect on specific growth rate (SGR) of both green and red variants A. japonicus (P < 0.05). Both colour variants of sea cucumber had highest SGR at 30 psu, and then decreased when salinity below or above this point. Maximum SGR (the green 1.07 ± 0.08% day^?1, the red 1.14 ± 0.09% day^?1 respectively) is related with maximum food intake (FI) and highest food conversion efficiency (FCE) (P < 0.05) occurring at 30 psu. Only under 22 psu, the green variant grew faster than the red variant (P < 0.05), and under other four salinity treatments there was no significant difference between SGR of two colour variant holothruians (P > 0.05). Values of adaptable salinity scope for green and red variants sea cucumber survival are 18.5~39 psu and 20.9~38.6 psu respectively. The average energy budget formula of sea cucumber at 30 psu was: 100C = 6G +42F +3U+49R (C, energy ingested; G, energy for growth; F, energy loss as faeces; U, energy used for ammonia excretion; R, energy loss for respiration). The sea cucumber had maximum energy ingested (C) and highest proportion of energy for growth (G) at 30 psu, and then decreased when salinity is above or below this salinity. Both red and green variants of A. japonicus deposited for growth were very low, and the energy loss in faeces and energy for respiration accounted for the majority of assimilation energy. The result clearly showed that the optimum condition for farming green and red variants A. japonicus, both with respect growth and energy allocation, is the salinity scope of 26 ~ 30 psu.     

Intra‐specific effects of sea cucumber (Apostichopus japonicus) with reference to stocking density and body size

The present studies deal with the intra‐specific effects of sea cucumber Apostichopus japonicus with unlimited food resources, especially the effects of stocking density on growth variation of the animal and energetic changes of small individuals under the stress of large individuals. The results showed that with the initial body weight of 5.12±0.09–6.11±0.26 g of sea cucumber among the densities of 5, 10, 20, 30, 40 and 50 ind./100 L, the density of 20 ind./100 L was the optimum stocking density because of its highest specific growth rate, crude protein content and crude lipid content in tissue. Individual growth variation of A. japonicus increased with the increase of stocking densities, whereas no significant differences in variation were found when the density was over 30 ind./100 L (P>0.05). The low‐weight individuals under the stress of heavy‐weight individuals exhibited obvious changes in energetics, such as lower ingestion rate, lower energy deposited as growth but higher respiration and excretion. The coefficient of variation in growth of the animals was over 70% due to the simultaneous action of aggression and maybe a factor of chemical mediator, and led to significant changes in the energetics of small‐sized individuals.     

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.     

刺参养殖池塘中新敌害生物澳洲异尾涡虫的鉴定及其危害

为了对导致辽宁大连、山东东营的2家养殖场池塘养殖刺参大量化皮死亡的新的敌害生物进行鉴定并确定其对养殖刺参的危害。本实验通过形态学观察、分子鉴定及系统发育分析确定了涡虫的分类地位,通过生态学方法确定了其生态适应条件,通过切割后培养的方法观测了其再生能力,通过与刺参苗种的共培养实验测试了该物种对刺参的危害及其危害方式。形态学观察结果显示,该涡虫体长0.96～3.26 mm,体宽0.49～1.93 mm,外观黄色或黄褐色,头部钝圆,具一对暗红色棒状眼点,尾部具两条并列的尾垂;显微镜镜检发现其表皮下分布密集的虫黄藻,体表周生纤毛,雌雄同体,口后具有两个生殖孔;对该物种COⅠ及18S r DNA基因片段扩增测序结果进行分析,并构建基于18S rDNA基因的系统发育树,结果显示该生物与澳洲异尾涡虫序列同源性达99.64%,根据其形态学特征,并结合18S rDNA分子鉴定结果,将该生物鉴定为澳洲异尾涡虫;进一步对其生活习性进行了研究,结果显示,该生物具有避光性,其适宜温度为18～24°C,适宜pH为5.5～8.0,适宜盐度为20～40;再生实验表明,该物种具有很强的前后轴极性再生能力;该生物与刺参的共培养实验表明,澳洲异尾涡虫对刺参体表表现出很强的趋向性,可以吸附在刺参体表导致刺参苗种溃疡、化皮甚至死亡,但刺参的体腔、肠道、呼吸树内均未发现虫体寄生。研究表明,澳洲异尾涡虫是营自由生活的池塘养殖刺参的一种新的敌害生物,在养殖过程中需要密切关注并防范该敌害生物。     

Single spaghetti tagging as a high-retention marking method for Japanese common sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

Populations of sea cucumbers, including the Japanese common sea cucumber Apostichopus japonicus, have been seriously depleted worldwide due to overfishing. Mark–recapture study is an efficient means of collecting ecological data. However, the use of such a method in sea cucumbers is difficult because they lack hard tissues in the body wall. Here we tested the viability of various tagging methods on A. japonicus. First, we applied conventional tags using four different methods [single spaghetti (T-bar) tagging, double spaghetti tagging, ribbon tagging, and Atkins tagging] to ten individuals per method in aquaria for 14 days. Of the methods used, single spaghetti tagging had the highest retention rate. Then we examined the retention rate of single spaghetti tags on ten individual sea cucumbers for up to approximately 6 months in rearing conditions. The single spaghetti tagging method showed a retention rate of 100% over at least 7 days, and 50% of the tags remained embedded after 56 days. The longest duration of tag retention was 174 days, at which time the experiment was terminated. These results indicate that single spaghetti tagging is reliable for both short- and longer-term studies, making it a useful tool for ecological and conservation studies in sea cucumbers.     

Winter longitudinal variation in the body size of larval fishes in the Seto Inland Sea,Japan

This study revealed the spatial variation in abundance and body size of larval fishes in the Seto Inland Sea, Japan, in January 2014 and 2015. Fish larvae were collected by a 1.3-m-diameter ring net towed at the surface and at 10-m depth at 21 stations. The most dominant species was the sandlance Ammodytes japonicus, constituting 82% of total larval fish caught. The body size of A. japonicus was greater [ca. 9 mm total length (TL) in 2014] in eastern areas than in western areas (ca. 5 mm TL in 2014). This trend was also observed in rockfishes (Sebastiscus marmoratus and Sebastes inermis species complex), suggesting a common phenomenon in this region. Because the water temperature was lower in eastern areas, it is likely that the longitudinal differences in larval body size are attributable to earlier spawning in eastern areas caused by different temperature conditions.     

Seasonal variations of immune parameters in the coelomic fluid of sea cucumber Apostichopus japonicus cultured in pond

In order to understand the effects of seasonal change on the immunity of sea cucumber Apostichopus japonicus cultured in pond, A. japonicus with body weight of 12.2 ± 4.5 g (sample A) and 32.6 ± 7.1 g (sample B), respectively, were collected monthly and randomly from a typical pond during a year cycle and employed for the evaluation of immunocompetence. Simultaneously, the environmental factors in the pond including water temperature, pH, salinity and dissolved oxygen (DO) were measured using a handheld multiparameter meter. The activities of acid phosphatase (ACP), alkaline phosphatase (ALP), lysozyme (LYZ), phenoloxidase (PO), superoxide dismutase (SOD), catalase (CAT) and myeloperoxidase (MPO) in the coelomic fluid were selected for the evaluation of A. japonicus immunocompetence and determined using biochemical methods. The results showed that in both samples, the activities of all determined enzymes had small values in winter and early spring, and LYZ, CAT and MPO activities also presented small values in summer, suggesting that pond‐cultured A. japonicus underwent immunosuppression twice during a year cycle, and the immunosuppression occurred in winter and early spring was more severe than that occurred in summer. In addition, most of the determined enzymes showed different variations between the two samples, and had significantly negative correlation with protein concentration, which was significantly and negatively correlated with water temperature, revealing that body weight and water temperature might have crucial effects on the immunity of A. japonicus cultured in pond.     

Effects of several factors on growth of milkfish (Chanos chanos Forskal) fingerlings reared with artificial diets in aquaria

This paper presents the effects of feeding level, feeding frequency, salinity of water, kind and particle size of diets, and stocking density on the growth of milkfish (Chanos chanos Forskal) fingerlings which were reared with artificial diets in laboratory tanks. Experimental groups were designed using orthogonal array L₈, and the results were evaluated statistically. Growth of the milkfish fingerlings varied markedly with the kind of diets used and feeding level. The feeding frequency and particle size of the diets also affected growth of the fingerlings significantly, but the salinity of the water did not. The weight gain of the fingerlings did not vary with the stocking densities significantly, whereas the increase (%) in body length was greater at a lower stocking density. The milkfish fingerlings showed the best growth in terms of both weight gain and increase in body length when reared on a purified diet containing 35% casein and 15% gelatin as protein sources under the following conditions: feeding level, 30–35% of body weight; feeding frequency, twice a day; particle size of diets, 125–250 μm diameter; and stocking density, $\text{5 fish}\text{5-liter}$ tank. The means and confidence limits of the weight gain (%) and increase (%) in body length of milkfish fingerlings under the best conditions adopted were estimated to be 360 ± 63.7 and 62.1 ± 10.6, respectively.     

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.     

Effect of salinity and temperature on salinity tolerance of the sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

Sea cucumber Apostichopus japonicus juveniles acclimated to different environmental conditions (23, 25, and 27°C combined with 25, 30, and 35 psu) were assessed for tolerance to increasing and decreasing levels of salinity at a rate of 2 psu h⁻¹. They were also tested for the LS₅₀ (median lethal salinity) when transferred directly into a series of higher salinity (32–46 psu) and lower salinity (9–25 psu). The CSMax (critical salinity maximum), CSMin (critical salinity minimum), USTL (upper salinity tolerance limit), and LSTL (lower salinity tolerance limit) were positively correlated to the acclimated salinity level but negatively correlated to temperature. The CSMax of A. japonicus was 6.2–10.0 psu higher than the USTL, and the CSMin was 5.5–8.5 psu lower than the LSTL, indicating that gradual changes in salinity resulted in the wide range of salinity tolerance that was observed, but that abrupt changes in salinity resulted in the narrow range of tolerance. Two-way analysis of variance revealed that salinity and temperature had a significant effect on 50% CSMax, 50% CSMin, USTL, and LSTL (P < 0.001). The information obtained in this study will be valuable for the further development of the sea cucumber aquaculture industry in China.     

Lentinan extracted from shiitake mushrooms (Lentinus edodes) improves the non-specific immunity of sea cucumber (Apostichopus japonicus)

In this study, the subpopulations of coelomocytes of sea cucumber Apostichopus japonicus were identified with differential-interference microscope and flow cytometry (FCM). The immunostimulatory potential of crude lentinan (cLNT) from shiitake mushrooms (Lentinus edodes) on A. japonicus was then investigated both in vitro and in vivo. In vitro, the coelomocytes of A. japonicus were incubated with different concentrations of cLNT (0, 2.5, 7.5, 22.5 mg/L) for 1 h, and immuno assays were performed. Flow cytometric analysis revealed that phagocytic activity and viability of coelomocytes increased significantly with cLNT treatment. Biochemical analysis showed a significant increase in peroxidase and alkaline phosphatase activity in coelomocytes. In vivo, the immunostimulatory effect of cLNT on coelomocytes was investigated with FCM by feeding A. japonicus with cLNT-supplemented or control diet for 24 days. The phagocytic activity of coelomocytes in cLNT treatment group was significantly increased at 4, 8 and 12 days of feeding. The viability of coelomocytes was increased after 8 days of feeding. At 4, 8, 12 and 18 days of feeding, the number of small-sized and low granularity coelomocytes was reduced, while the number of large-sized and high granularity coelomocytes was increased compared to control diet. Collectively, our in vitro and in vivo studies suggest that cLNT derived from L. edodes clearly reveals immunostimulating effects on A. japonicus by increasing the viability and phagocytic activity of coelomocytes, and these findings suggest that dietary supplementation of cLNT might further improve the commercial production of sea cucumbers.     

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.     

Growth and oxygen consumption of the juvenile sea cucumber Apostichopus japonicus (Selenka) at constant and fluctuating water temperatures

The effects of thermal amplitudes of diel fluctuating temperature on growth and oxygen consumption of the juvenile sea cucumber Apostichopus japonicus (Selenka) were studied at the average temperatures of 15 and 18°C with three diel different fluctuating amplitudes of ±2, ±4 and ±6°C. The optimum thermal amplitudes for growth of the juvenile sea cucumber at the sizes of this experiment, at average temperatures of 15 and 18°C, were estimated to be ±1.38 and ±1.67°C respectively. In the constant temperature regimes, the growth rate at 15°C was higher than that at 18°C. However, the growth rate at 18±2°C was higher than that at 15±2°C. The results from this study suggested that fluctuating temperatures enhanced the optimum temperature for the growth of sea cucumbers compared with that at constant temperatures. Therefore, accurate predictions of the optimum temperature of sea cucumbers in the natural environment, in which water temperatures fluctuate daily and seasonally, should be made from data obtained at fluctuating temperatures.