Intensive rearing of juvenile crayfish (Pacifastacus leniusculus,Astacidae) during the first 6 months: effects of size grading

Recent advances in crayfish feeding have enabled the development of size grading studies from the start of first‐feeding. A 180‐day experiment aimed at intensive rearing of Pacifastacus leniusculus was carried out under controlled conditions, evaluating the effects of size grading at two different periods from the onset of exogenous feeding. Stage 2 juveniles were stocked in fibreglass tanks at a density of 100 m², and fed a dry diet for salmonids combined with restricted amounts of Artemia cysts. Five groups were tested: no grading, grading at 60 days (large and small size) and grading at 100 days (large and small size). After 6 months, no significant differences were found in the survival among groups (mean: 73.06%). The highest final growth (pooled results from upper and lower classes: 17.39 mm carapace length, 1.43 g weight) was achieved by the crayfish sorted at 60 days, showing significant differences from the ungraded group. Smaller crayfish graded at 60 days grew significantly faster than smaller crayfish graded at 100 days. The food conversion ratio was lower in the graded groups (mean: 2.64), showing significant differences from the ungraded group (3.23). This study shows that size grading allows a better performance and an improved feeding efficiency.     

Shelter and lighting in the intensive rearing of juvenile crayfish (Pacifastacus leniusculus,Astacidae) from the onset of exogenous feeding

Recent advances on feeding in intensive rearing of juvenile astacids enable research of other factors influencing growth and survival without the confounding effect of inadequate feeding. Two experiments were conducted to evaluate the effects of the number of shelters per crayfish and to test different lighting conditions. Stage 2 juvenile Pacifastacus leniusculus were stocked in fibreglass tanks and fed a dry diet for salmonids combined with restricted amounts of decapsulated Artemia cysts. In experiment 1, four, two or one shelters per crayfish were tested for 80 days. No significant differences were found among groups either in survival (final mean: 86.67%) or in growth [final mean: 11.41 mm mean carapace length (CL), 355.45 mg mean weight]. In experiment 2, three lighting conditions were tested for 120 days: continuous lighting of 925 lx, continuous darkness and natural photoperiod. Survival rates ranged from 76.7% to 88.3%, with no significant differences among groups. The crayfish kept under continuous darkness grew faster (final mean: 12.70 mm CL, 543.08 mg weight) than those reared under the other two light conditions. This study shows that, under improved feeding conditions, a minimum number of shelters can be provided, and faster growth can be obtained in continuous darkness.     

Effects of bottom substrate and presence of shelter in experimental tanks on growth and survival of signal crayfish, Pacifastacus leniusculus (Dana) juveniles

The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m^?2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials.     

Effects of fishmeal replacement by feather meal in practical diets for juvenile crayfish (Pacifastacus leniusculus Dana,Astacidae)

The aim of this study was to evaluate different replacement levels of fishmeal (FM) by feather meal (FeM) on survival and growth of juvenile crayfish (Pacifastacus leniusculus). An 80‐day experiment was conducted with stage 2 juveniles from the onset of exogenous feeding. Four practical diets (500 g kg^?1 protein) differing in the level of replacement of FM protein by FeM protein were prepared: 0% (control diet), 15% (8.2% dietary FeM), 25% (13.7% dietary FeM) or 35% (19.2% dietary FeM). Each diet was tested on grouped or individually isolated crayfish. Crayfish fed the control diet or 15% replacement achieved the highest survival (average of grouped and isolated: 88.2%) and growth (grouped and isolated: 13.58 mm carapace length, 523.2 mg weight) and the lowest feed conversion ratio (average of grouped and isolated: 1.11). Final growth of isolated crayfish was significantly higher than that of grouped crayfish for all diets. This study provides the first data on the substitution possibilities of FM by FeM in diets for freshwater crayfish. An 8.2% of FeM (15% replacement of FM protein) can be included in extruded diets for juvenile P. leniusculus during the first 80 days of intensive rearing without impairing growth or feed conversion.     

Effects of vitamin A inclusion in practical diets on survival and growth of juvenile crayfish (Pacifastacus leniusculus Dana,Astacidae) from the onset of exogenous feeding

The aim of this study was to evaluate the effects of practical diets with different levels of vitamin A on survival and growth of juvenile crayfish (Pacifastacus leniusculus). An 80‐day trial was conducted with stage 2 juveniles from the onset of exogenous feeding. Four diets differing in the level of retinyl acetate were tested: 0, 0.0025, 0.0050 or 0.0100 g kg^?1 diet, equivalent to 0, 2500, 5000 or 10 000 IU vitamin A kg^?1 diet, respectively. Each diet was tested on grouped or individually isolated crayfish. Crayfish fed the diet with 5000 or 10 000 IU vitamin A kg^?1 diet achieved the highest survival (average of grouped and isolated: 88.9%) and growth (grouped and isolated: 13.45 mm carapace length, 533.4 mg weight). Final growth of isolated crayfish was significantly higher than that of grouped crayfish for all diets. This study provides the first data on vitamin A requirements of freshwater crayfish. A level of 5000 IU vitamin A kg^?1 can be recommended for juvenile P. leniusculus during the first period of intensive rearing.     

A comparison of the growth and survival of two freshwater crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), under different temperature and density regimes

Growth experiments carried out with two juvenile crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), at different temperatures and densities highlighted the problem of cannibalism under conditions aimed at intensifying crayfish production. Cannibalism proved to be much lower in A. leptodactylus than P. leniusculus, suggesting that the former might be the better candidate for astaciculture. In the first of two population survival trials, A. leptodactylus showed a higher survival rate than P. leniusculus, with 26% of P. leniusculus surviving in the first replicate, compared to 42.3% of P. leniusculus, and 40.76% surviving in the second replicate, compared to 47.6% of P. leniusculus. The same trend was observed in the second experiment, with P. leniusculus showing survival rates of 48.5 and 55.3% (first and second replicates, respectively) in comparison to 65.2 and 68.2%, respectively, for A. leptodactylus. It is therefore highly likely that if P. leniusculus were to become established in Turkey, it would outcompete the native A. leptodactylus even if it were not to be devastated by the crayfish plague that has decimated the native species. The experiments also highlighted the problem of differential growth, with some juveniles hardly growing at all while others reached a relatively large size. The range in carapace length (CL) was 9–18 mm for A. leptodactylus and 8.5–18.5 mm CL for P. leniusculus at the end of the first experiment. While both species grew quickly, P. leniusculus hatched earlier, giving it an advantage over A. leptodactylus; consequently, by the end of the summer, the juveniles of the former were larger than those of A. leptodactylus. Specific growth rate values showed that the juveniles of the two species had similar growth rates. The results also revealed that growth was not significantly affected by density in both species at 15°C, but at 25°C, growth was significantly better at a density of 234 juveniles m⁻² than at 468 juveniles m⁻², and better at 468 juveniles m⁻² than at 937 juveniles m⁻² (P < 0.01 and P < 0.001, respectively). We conclude that P. leniusculus is a good candidate for aquaculture as it has a rapid growth rate and early hatching and maturity; however, its aggressive behavior may make it a less attractive proposition than A. leptodactylus, which is also fast growing but less aggressive. This study is a part of PhD study of M.M. Harlıoğlu, who is supported by Fırat University Elazığ, Turkey.     

Effects of vitamin C inclusion in practical diets on survival and growth of juvenile crayfish (Pacifastacus leniusculus Dana,Astacidae) from the onset of exogenous feeding

The aim of this study was to evaluate the effects of practical diets with different levels of vitamin C on survival and growth of juvenile crayfish (Pacifastacus leniusculus). An 80‐day trial was conducted with stage 2 juveniles from the onset of exogenous feeding. Four practical diets differing in the content of l ‐ascorbyl‐2‐monophosphate‐Na were prepared: 0, 0.2, 0.4 or 0.8 g kg^?1 diet. Each diet was tested on grouped or individually isolated crayfish. Diets had no significant effects on survival of crayfish held in groups (average: 73.1%) neither on the isolated ones (average: 90%). Crayfish fed the diet with 0.2 g kg^?1 of l ‐ascorbyl‐2‐monophosphate‐Na had the highest growth (groups: 13.64 mm carapace length (CL), 542.4 mg weight; isolated: 17.05 mm CL, 1213.2 mg weight) and the lowest feed conversion ratio (average of grouped and isolated: 0.99). This study provides the first data on vitamin C requirements of freshwater crayfish. A level of 0.2 g l ‐ascorbyl‐2‐monophosphate‐Na kg^?1 diet (0.07 g ascorbic acid equivalent) can be recommended for juvenile P. leniusculus during the first period of intensive rearing.     

温度、盐度和光照周期对刺参生长及行为的影响

刺参(Apostichopus japonicus)产于我国北方海区,是一种名贵的水产品,肉质肥厚,营养丰富,为海参之上品[1]。长期以来,由于滥捕滥采,自然资源日趋衰减。近年来,随着刺参人工育苗及人工养殖技术的成熟,刺参增养殖业从海区底播增殖、池塘养殖、虾池混养到陆地工厂化养殖,发展很快[2-6]。一些学者对刺参的生理生态学、行为学等方面进行了研究[7-9],但关于环境因子对刺参的生长和行为影响的研究报道不多[10]。笔者观测了不同温度、盐度和光照周期这3个环境因子对刺参生长及行为的影响,旨在确定最适合刺参生长的环境条件,为推动刺参的增养殖业的…     

高温和低氧胁迫对两种规格刺参半致死时间及生理机能的影响

通过实验生态学方法,针对2种规格的刺参(Apostichopus japonicus)(大:28.00~36.00 g;小:9.00~13.00 g),测定温度为(25.0±0.5)℃溶解氧(DO)水平为(1.0±0.1)mg/L条件下刺参的半致死时间(LT_(50));比较分析了DO水平分别为(1.0±0.1)mg/L、(3.0±0.1)mg/L及6.5 mg/L(正常DO含量)条件下2种规格刺参的昼夜代谢水平;监测了DO水平分别为(1.0±0.1)mg/L和(3.0±0.1)mg/L时低氧胁迫24 h及复氧72 h期间,2种规格刺参体腔液和呼吸树中的谷胱甘肽(GSH)含量、总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性及体腔液中皮质醇水平的变化,以探究夏季高温期(25.0±0.5)℃低氧胁迫对不同规格刺参半致死时间及生理机能的影响。结果显示:当DO浓度为1 mg/L时,大规格刺参半致死时间(LT_(50))为33.37 h,小规格刺参为28.84 h,2种规格刺参的代谢水平显著低于常氧对照组,夜间代谢强度高于白天,且小规格刺参的代谢强度高于大规格刺参。1 mg/L低氧胁迫期间,大规格刺参体腔液及2种规格刺参呼吸树中上述4种抗氧化指标的变化趋势大致相同,与对照组相比,随着低氧暴露时间的延长,GSH含量下降,SOD和T-AOC活力降低,CAT活力升高;然而胁迫结束时其GSH含量、CAT、SOD和T-AOC活力均与对照组无显著差异(P0.05)。解除胁迫复氧72 h后,2种规格刺参体腔液的4种抗氧化指标均恢复到对照组水平;而呼吸树的这4种指标则未完全恢复。3 mg/L低氧胁迫期间,2种规格刺参体腔液和呼吸树的GSH含量、CAT、SOD和T-AOC活力的变化趋势与1 mg/L组大体一致,复氧72 h后体腔液的各项指标恢复到对照组水平;除T-AOC,呼吸树的其余3种指标亦完全恢复。低氧胁迫后小规格刺参的恢复能力高于大规格刺参。在DO为1 mg/L和3 mg/L条件下,胁迫结束时2种规格刺参体腔液中的皮质醇含量显著高于对照组(P0.05),且大规格刺参皮质醇含量高于小规格,复氧后二者均恢复到对照水平。结果表明,低氧胁迫持续时间不超过其半致死时间(本研究以24h为例),刺参可通过自身调节减轻机体的氧化损伤;一旦超出半致死时间,将产生不可逆损伤,最终导致死亡。     

Determination of the optimal water temperature for the culture of juvenile dusky kob Argyrosomus japonicus Temminck and Schlegel 1843

The effects of temperature on growth, food-conversion ratio (FCR) and feeding intensity of juvenile dusky kob Argyrosomus japonicus (23.7±2.6 g fish⁻¹) were assessed over the temperature range 17.5–28.5 °C in a 42-day growth trial. Growth increased with increasing temperature up to an optimum after which it declined. Specific growth rates were 2.05% and 1.2% day⁻¹ for the fastest (25.3 °C) and the slowest (17.5 °C) treatments respectively. Food-conversion ratio peaked at a lower temperature than growth. Optimal (0.72 kg kg gain⁻¹) and least efficient (1.40 kg kg gain⁻¹) FCR were found at 21.7 and 17.5 °C respectively. Feeding intensity was linearly related to temperature within the range of 17.5–28.5 °C. These results corresponded to the thermal preference (25–26.4 °C) and natural temperature distribution (12–28 °C) of South African dusky kob. Determination of the temperature range that does not limit growth is a prerequisite to assess the relationship between growth and environmental variables such as light intensity, feeding regime and stocking density. Consequently, experiments to determine the effects of these environmental variables on growth and aquaculture potential of dusky kob should be conducted at 24–26 °C.     

Effect of high water temperature on the survival, moulting and food consumption of Penaeus (Marsupenaeus) japonicus (Bate, 1888)

The kuruma shrimp, Penaeus (Marsupenaeus) japonicus (Bate, 1888), is a valuable aquaculture species in Queensland, Australia. The shrimp is supplied live to the Japanese market and must survive emersed transport for up to 36 h. In-transit mortality after harvest from high water temperatures (> 30 °C) has been reported by the industry, and a knowledge of the effects of high water temperature may provide important information for producers on grow-out management, timing of production and farm location. Experiments were conducted to determine the effect of high water temperature on survival, moulting and food consumption in P. japonicus. Replicated groups of 15.6 ± 0.2 g shrimp were acclimated and exposed to five temperatures, between 28 and 36 °C, for up to 28 days. Mortality was highest at 36 °C and equally lowest between 28 °C and 32 °C. Intermoult period was not significantly different for temperatures between 28 and 32 °C (19.8–15.5 days) but was significantly greater above 32 °C (27.4 days at 34 °C and > 104 days at 36 °C). There was evidence of moulting synchrony at 28 °C. Mean daily food consumption was highest at 32 °C at 2.34% of body weight, but decreased to 1.56% at 28 °C and 1.33% at 36 °C. Over the range of water temperatures examined, survival, moulting rate and food consumption were highest at 32 °C.     

Growth of larval and early juvenile Japanese anchovy, Engraulis japonicus, in the Kuroshio-Oyashio transition region

Larvae, juveniles, and adults of Japanese anchovy, Engraulis japonicus , were distributed throughout the Kuroshio-Oyashio transition region off northern Japan as far offshore as 170°E in 1996 and 1997. The growth trajectories of individual larvae and early juveniles were backcalculated using the biological intercept method based on the allometric relationship between otolith radius and somatic length. Mean larval growth rates ranged from 0.49 to 0.71 mm day^–1 in the transition region, and were comparable to those reported from the Pacific coastal waters of central Japan, which is the principal distribution range of E. japonicus . In terms of growth, the Kuroshio-Oyashio transition region seemed to be a favourable nursery area for larval E. japonicus . Larval growth tended to decline from the inshore to the offshore waters in the transition region. Thermal conditions did not show an inshore–offshore trend in the survey area and did not explain the longitudinal trend in growth rates.     

Comparison of spatiotemporal patterns in reproduction of the kuruma prawn Marsupenaeus japonicus between two regions having different geographic conditions in Kyushu, southern Japan

ABSTRACT:   The Yatsushiro Sea and Shibushi Bay are, respectively, located on the western and south-eastern coast of Kyushu, southern Japan. The Yatsushiro Sea is a shallow semi-enclosed inland sea, whereas Shibushi Bay is an open-type bay with a deep and wide mouth facing the open sea. The size at sexual maturity and spatiotemporal patterns of reproduction of the kuruma prawn Marsupenaeus japonicus (Decapoda, Penaeidae) were examined and compared between these two regions. In the Yatsushiro Sea, the size at sexual maturity was estimated to be 131 mm body length. However, the estimated size at sexual maturity was considerably larger (154 mm) in Shibushi Bay. The spawning season of M. japonicus was estimated to continue from April to September in the Yatsushiro Sea, whereas it was estimated to be longer in Shibushi Bay, from March to November. It is believed that the warm water temperature due to the strong effect of the Kuroshio Current prolonged the spawning season of M. japonicus in Shibushi Bay. The spawning grounds were estimated to be in areas deeper than 10 m in the Yatsushiro Sea and deeper than 20 m in Shibushi Bay. In Shibushi Bay, body size distribution of mature females was considered to be less affected by water depth in comparison with the Yatsushiro Sea, although older mature females larger than 200 mm body length also spawned outside of the bay.     

Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

Abstract  This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout.     

Differences in feeding,intestinal mass and metabolites between a thermotolerant strain and common Apostichopus japonicus under high summer temperature

Two groups of Apostichopus japonicus, a thermotolerant strain (group G3: wet weight, 64.22 ± 13.16 g/ind.), which was selected focusing on the performance of thermo‐tolerance through three generations for 10 years, and a control group (group C: wet weight, 62.08 ± 12.01 g/ind.) were collected from July to October in a seawater pond in northern China. Differences in relative faecal mass (RFM), relative intestinal mass (RIM), percentage of individuals with faeces (PIWF) and intestinal metabolites were investigated and compared between the two groups. The temperatures of terminating aestivation of the two groups were assessed according to the values of RFM and RIM. A regression analysis showed that the corresponding group G3 temperatures were 0.56–1.34°C and 0.70–1.49°C higher than those of group C when RFM and RIM were 0.01–0.05 and 0.005–0.025 respectively. The PIWF values in group G3 were 11.5%–21.2% higher than that in group C from 20 July to 22 September. Significant differences at the concentrations of 52 metabolites were detected between the two groups, 36 were higher in group G3 and 16 were higher in group C. The concentrations of threitol, 2‐methylglutaric acid, N‐acetyl‐D‐galactosamine, N‐acetyl‐L‐leucine, lactose, oxoproline, 2,3‐dimethylsuccinic acid and d‐glucoheptose were significantly different between groups G3 and C and were considered metabolic markers distinguishing group G3 from group C. Metabolism of A. japonicus in group G3 was more active than that in group C. These results provide new insight for understanding ingestion and intestinal metabolism in the thermotolerant strain of A. japonicus under high summer temperature.     

Relationship between daily survival rates of larval Japanese anchovy (Engraulis japonicus) and concentrations of copepod nauplii in the Seto Inland Sea, Japan

We attempted to estimate the survival rates of larval cohorts (3–15 mm in body length) of the Japanese anchovy Engraulis japonicus population in Hiuchi‐nada, Seto Inland Sea, Japan, and examined the relationship to their food availability. The survival rates were directly calculated from the change in larval density during the survey. The estimated daily survival rate ranged between 0 and 89% d⁻¹, but increased with the increase in the mean concentration of small‐sized copepod nauplii (<100 μm in body length) sampled at 10 m depth. When the food concentration was higher than about 5 nauplii L⁻¹, the daily survival rate of larval anchovy reached an asymptote of approximately 89% day⁻¹. It might be possible to provide a framework for the forecast for larval abundance immediately prior to recruitment size (10–15 mm SL), based on larval abundance of the monitored size (3–8 mm SL) and the survival rate which is estimated from the concentration of small‐sized nauplii.     

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.     

Linking environmental drivers,juvenile growth,and recruitment for Japanese jack mackerel Trachurus japonicus in the Sea of Japan

Growth traits of juvenile Japanese jack mackerel (Trachurus japonicus) were estimated based on otolith daily increments in spring during 2011–2016 in the southwestern part of the Sea of Japan (SWSJ). Spatial variability in growth traits was examined between the western and eastern areas of the study area. Back-calculated body length at 50 days post hatch varied among areas and years between 26 and 40 mm. Body lengths at age in the eastern area were significantly smaller than those in the western area. Slower growth rate in the eastern area was associated with the lower ambient temperature in the eastern area than in the western area. In the eastern area, interannual variations in the instantaneous growth rate positively correlated with ambient temperature. Furthermore, interannual variations in back-calculated body length during the late larval and early juvenile stages positively correlated with the juvenile abundance. These results suggest that the thermal conditions in the eastern area are indicative of the growth rate and abundance of juvenile T. japonicus in SWSJ. We further examined relationships between juvenile abundance and thermal conditions during 2003–2019 using archived data of this survey and found that the ambient temperature in the eastern area positively correlated with the juvenile abundance and also the strength of the Tsushima Warm Current. Thus, higher temperatures derived from the Tsushima Warm Current result in a faster growth rate during the late larval and early juvenile stages and subsequently higher abundance of T. japonicus juveniles in SWSJ.     

Assessment of requirement values for essential amino acids in the prawn, Marsupenaeus japonicus (Bate)

The requirements of juvenile prawn, Marsupenaeus japonicus (Bate), 0.79 g initial body weight, for essential amino acids (EAA) were evaluated based on the daily increase of each EAA in the whole body when the prawn was maintained on a diet with a high nutritive value (a casein‐squid protein‐based diet). The quantities of each EAA needed daily for growth and maintenance of prawn are conceived to correspond to the daily requirements of this prawn species for EAA. Therefore, these requirement values of respective EAA should be supplied from dietary proteins. To determine these values, protein and amino acids of the whole body of the prawn were quantified before and after feeding experiments, and the quantities of respective EAA needed to meet the requirements were estimated based on the EAA profile of the whole body protein of prawn. As a result, the contents of EAA in dietary proteins (%) needed to meet the requirements of the prawn for EAA were assessed to be: threonine (2.3), methionine (1.3), valine (2.4), isoleucine (2.3), leucine (3.4), phenylalanine (2.6), lysine (3.2), histidine (1.1), arginine (2.9) and tryptophan (0.6), respectively, when the prawn are fed 50% protein diet with 90% protein digestibility at a ration size of 2% (% of body weight).     

A new system for the culture and stock enhancement of sea cucumber,Apostichopus japonicus (Selenka),in cofferdams

A new multilayer, plate‐type system for the culture and stock enhancement of sea cucumbers in cofferdam was developed. To optimize and evaluate the system, four experimental designs were implemented using polyethylene (PE)‐corrugated sheets of various colours, interval spacing and shapes/styles. Results showed that a system equipped with black PE‐corrugated sheets attracted more animals than either blue, green, transparent or a selection of mixed sheets (six transparent sheets in the upper layer and five black sheets in the lower layer) (P<0.05). Also, more animals gathered in the system with oblique‐angled sheets (30° to the base plate) than either a wavy (the bottom and every second sheet was at an angle of 10° to the base plate) or parallel arrangement (P<0.05), and more animals assembled in the system with 2 cm between sheets than spacings of 3, 4 or 5 cm (P<0.05). As expected, the upper layers of the systems attracted more animals than lower layers in most cases except for those with transparent and mixed oblique‐angled sheets with a 3 cm spacing (P<0.05). Thus, a system with black, oblique‐angled‐corrugated sheets and 2 cm spacing is recommended for Apostichopus japonicus (Selenka) culture and stock enhancement in cofferdams or ponds.