Bioeconomic analysis of intensive production of the blue shrimp Litopenaeus stylirostris (Stimpson)

A bioeconomic approach was used to evaluate random variation of growth and mortality parameters and feed conversion ratio (FCR) for intensive production of the blue shrimp Litopenaeus stylirostris (Stimpson). Severe mortality problems caused by high impact diseases were not considered in this analysis. For a 50‐ha farm, the maximum values of the internal rate of return (IRR=44%) and net revenue above operation costs (NR=US$1 211 000) were obtained for a stocking density of 67 postlarvae (PL) m^?2 during winter–spring (cycle 1) and 65 PL m^?2 during summer–autumn (cycle 2). Regardless of the density used for cycle 1, stocking at 50 and 65 PL m^–2 for cycle 2 sufficed to obtain, respectively, IRRs greater than the minimum attractive IRRs of 15% and 30%. A frequency distribution of IRR, projected for densities of 67 and 65 PL m^?2, showed high confidence in obtaining IRR values above 15% and 30% (i.e. confidence >99% and 92% respectively). The frequency distribution of NR showed that the farm could operate without economic losses. Stocking a minimum of 53% of the capacity of the farm would guarantee positive NR. Sensitivity analysis indicated that the IRR and NR were mainly influenced by mortality rate, selling price, density, final weight and FCR.     

Allozyme genetic analysis in hatchery strains and wild blue shrimp, Penaeus (Litopenaeus) stylirostris (Stimpson), from the Gulf of California

We conducted a population genetic analysis of Penaeus stylirostris to describe the genetic variability in two wild samples (Guaymas and Peñasco) and in two cultivated strains (A and B), and to determine the relationship among samples. Seventeen enzymatic systems and general proteins were used to visualize 31 loci. Of the 31 loci, 11 polymorphic loci (35%) were detected in all the organisms, with an average heterozygosity of 0.10 and an average of 1.8 per locus. There were no significant differences among the four samples of observed heterozygosity or percentage of polymorphic loci. According to Hardy–Weinberg, both cultivated strains showed disequilibrium in more loci than the wild samples. Guaymas showed linkage disequilibrium in five pairs of polymorphic loci, Peñasco samples in two pairs, A in seven pairs, and B in nine pairs. Peñasco and both cultivated lineages showed evidence of recent reductions in their effective populations size. Based on the comparisons of F_st values, and the distribution of the allelic frequencies, the cultivated strains were significantly different from the two wild populations. There is evidence that strain B originated from A and the discrepancies between the strains are probably the result of genetic drift and a founder effect.     

Promotion and contribution of biota in low water exchange ponds farming blue shrimp Litopenaeus stylirostris (Stimpson)

An experimental study was conducted during 20 weeks in Bahia Kino, Sonora, Mexico, in order to evaluate the feasibility of promoting biota in low‐water exchange ponds farming blue shrimp, Litopenaeus stylirostris. The effect of that promotion on the production parameters of cultured shrimp as well as on the water quality parameters was evaluated. Treatments consisted of: (i) ponds fed formulated food (FF), and (ii) ponds fed formulated plus promoted natural food (NFF). Phytoplankton, zooplankton and benthos were effectively promoted during some weeks of the culture period. Growth and feed conversion ratio (15.16 g and 1.79 respectively) were significantly better in treatment NFF than in treatment FF (13.89 g and 2.02 respectively). Differences in some of the water quality parameters were observed among treatments. Phosphates (0.15 mg/L versus 0.53 mg/L), and total ammonia‐N (0.09 mg/L versus 0.12 mg/L) presented greater concentrations in treatment FF than in the NFF.     

Apparent digestibility coefficient of nutrients from shrimp,mussel, diatom and seaweed by juvenile Holothuria scabra Jaeger

The ability of Holothuria scabra to digest nutrients, such as organic matter (OM), protein and carbohydrate from animal and plant feed ingredients was investigated. Four test feeds prepared by mixing sand with single ingredients from animal sources (shrimp and mussel) and plant sources (diatom and seaweed) were fed to H. scabra to estimate apparent digestibility coefficient (ADC). The total assimilated nutrient (TAN) increased with ADC, whereas ingestion rate (IR) varied slightly among the feeds suggesting that ADC might be a good indicator of nutrient availability to H. scabra. The ADC_OM of shrimp and mussel was significantly higher than that diatom and seaweed: 86.2%, 77.1%, 55.1% and 32.3% respectively. ADC_protein was similar for shrimp (88.7%), mussel (84.8%) and diatom (75.2%), but significantly lower in seaweed (34.4%). ADC_carbohydrate was similar in mussel (58.5%) and diatom (58.3%) as well as in seaweed (31.6) and shrimp (28.0%). ADC_protein was relatively higher than ADC_carbohydrate suggesting that H. scabra generally digests more protein than carbohydrate. Furthermore, results indicated that nutrients from animal‐based feeds are more efficiently digested by H. scabra; thus, animal ingredients rich in easily digestible protein could potentially provide an efficiently balanced diet for H. scabra fed with diatom containing high easily digestible carbohydrate.     

Biotic communities and feeding habits of Litopenaeus vannamei (Boone 1931) and Litopenaeus stylirostris (Stimpson 1974) in monoculture and polyculture semi-intensive ponds

Zooplankton, macrozoobenthos and feeding habits of Litopenaeus stylirostris and L. vannamei in monoculture and polyculture semi‐intensive experimental ponds were evaluated. Zooplankton was more abundant in monoculture of L. stylirostris (1002±670 organisms (org.) L^?1) than in monoculture of L. vannamei (470±37 org. L^?1), and polyculture (321±188 org. L^?1). The main zooplanktonic groups were polychaeta larvae, nauplii, copepods and polychaeta. Macrozoobenthos was more abundant in polyculture (6898±11 137 org. m^?2) compared with monoculture of L. stylirostris (3201±350 org. m^?2) and L. vannamei (2384±3752 org. m^?2). The main benthic groups were copepods, polychaeta, ostracods, nematodes and insects. Differences in feeding habits were found between species and regimes. Litopenaeus vannamei showed to be a more voracious species and fed mostly on organic detritus and benthos in both culture regimes. Litopenaeus stylirostris had a more restricted sources of feed in the ponds. The major component in the stomach content of both species was detritus. Macroalgae, sand, exuvia, formulated feed, prey and microalgae were minor components for both species (<7%). Ingestion of formulated feed was <4% for L. stylirostris and was not detected for L. vannamei. The stomach repletion rates were larger for L. vannamei (55.6% and 48.8%) than for L. stylirostris (43.75% and 44.89%). Litopenaeus stylirostris grew better in polyculture (10.3±3.4 g) that in monoculture (9.0±3.8 g). Litopenaeus vannamei grew better in monoculture (16.1±4.8 g) than in polyculture (13.4±4.5 g). For both species, feed conversion ratio was lower in polyculture.     

Response of blue shrimp Litopenaeus stylirostris (Pérez-Farfante & Kensley, 1997) to dietary cadaverine supplementation

Recent studies on salmon and shrimp have shown that reduced feed intake and growth caused by the consumption of low‐quality fish meals, manufactured from spoiled fish, were not due to the presence of biogenic amines. Moreover, an improvement in weight gain was seen in blue shrimp fed a diet supplemented with cadaverine plus histamine. It was not clear, however, if this effect was due to the consumption of histamine or cadaverine. The objective of the current experiment was to investigate the effect of dietary cadaverine supplementation on growth parameters and various amine concentrations in tissues of the blue shrimp Litopenaeus stylirostris. Six experimental diets were supplemented with cadaverine at 0, 500, 1100, 2300, 3500 and 4600 mg kg^?1 and tested in a feeding trial lasting 28 days. Feed consumption, feed conversion ratio, survival and weight gain were not affected by the concentration of dietary cadaverine. The dietary supplementation of cadaverine, however, resulted in a linear increase in cadaverine concentration in shrimp tissues, especially in the hepatopancreas. It was concluded that dietary cadaverine does not have any effect on growth and feed intake of shrimp. Growth promotion, as reported previously in shrimp fed a diet supplemented with histamine plus cadaverine, was probably due to histamine or a combined effect of histamine plus cadaverine but not due to dietary cadaverine alone. It seems that shrimp have a limited ability to metabolize cadaverine, which then accumulates intact in shrimp tissues.     

Dietary protein level and natural food management in the culture of blue (Litopenaeus stylirostris) and white shrimp (Litopenaeus vannamei) in microcosms

The effect of dietary protein level and natural food management on the production parameters of blue and white shrimp, as well as on water quality, was evaluated in a microcosms system (plastic pools simulating aquaculture ponds). Two experimental trials were carried out in the facilities of DICTUS, University of Sonora, Northwest México. Treatment with low protein diet (LP) consisted of a low protein input (diet with 250 g kg^?1 crude protein) through the culture period; treatment with high protein diet (HP) consisted of a high protein input (diet with 400 g kg^?1 crude protein) through the trial, and finally treatment VP consisted of an adjustment of protein input (diets with 250, 350 or 400 g kg^?1 crude protein), depending on the abundance of biota (zooplankton and benthos) in the system. Each species responded differently to the treatments. For blue shrimp, low protein input resulted in the lowest final body weight (12.9 ± 0.6 g) and biomass (696.0 g pool^?1). Survival and feed conversion ratio were similar in the three treatments. For white shrimp, the best growth, biomass and food conversion ratio were obtained in the low protein input treatment. Water quality parameters such as nitrate, ammonia and organic matter during the two trials, were better for LP and VP treatments. White shrimp seems to have lower protein requirements than blue shrimp. For the blue shrimp culture, adjusting protein input according to natural food abundance (zooplankton and benthos) in the system, seems to be advantageous because of the possibility of getting a production similar to that obtained with a high protein input through the farming period, but at lower feed cost, and with a lower environmental impact. It is concluded that a high protein input through the whole farming period is not the best feeding strategy for any of the two species.     

Preliminary assessment of large‐scale co‐culture of sandfish (Holothuria scabra) with the Babylon snail (Babylonia areolata) in earthen ponds and in raceways

Holothuria scabra (sandfish) and Babylonia areolata were trialed in two large‐scale co‐culture experiments. Experiment 1 assessed co‐culture in 4 × 400 m² earthen ponds where Babylonia were cultured in a central pen at a density of 400 individuals/m² with sandfish occupying the remaining pond space at 1.1 individuals/m². Sandfish grew from 18.20 ± 6.67 g to 119.03 ± 17.74 g in 92 days and Babylonia (fed trash fish in both experiments) grew from 0.90 ± 0.38 g to 4.93 ± 1.44 g, but Babylonia growth was not increased in co‐culture compared to monoculture. Water and sediment quality varied between co‐culture and monoculture ponds. Neither showed clear improvement due to sandfish culture. Experiment 2 compared non‐segregated sandfish‐Babylonia co‐culture with Babylonia monoculture in 20 m² concrete raceways. Sandfish were cultured at 2 individuals/m² and Babylonia at 300 individuals/m². Sandfish grew up to 1.91 g.day^?1 with 100% survival. Babylonia weight gain was significantly greater in co‐culture raceways (3.35 ± 0.64 g over 61 days), which was double that of Babylonia in monoculture. Substrate total N was reduced by 20% in co‐culture compared with monoculture (p = .032). This provisional study of commercial scale sandfish‐Babylonia co‐culture demonstrates culture compatibility, providing a basis for further system development.     

Experimental co-culture of low food-chain organisms, Sabella spallanzanii (Polychaeta, Sabellidae) and Cladophora prolifera (Chlorophyta, Cladophorales), in Porto Cesareo area (Mediterranean Sea)

The filter feeder polychaete Sabella spallanzanii (Gmelin) was co‐cultured with the green seaweed Cladophora prolifera (Roth.) Kunz, in an off‐shore experimental system. Both species have previously been experimented as bioremediator organisms for waste treatment deriving from aquaculture farms and can have a high economic value as a byproduct of polyculture. The present experiment has been conducted in an area 2 miles off the coast of Porto Cesareo (Ionian sea, Southern Italy). The growth was followed in some modules anchored to the bottom at two different depths (15 and 25 m depth). The results indicate differences among replicates located at different depths. Both organisms show a faster growth at the shallower levels. Within this level, polychaetes reached a mean biomass of 860±74 mg dw (average±SE) per worm, 30 times larger than that of the starting point, after a standstill in the first period, probably due to the manipulation activities. The major growth has been recorded during the winter. Algae have shown an increase of 34 g ww month⁻¹ (average±SE) in the shallower levels vs. only 11 g ww month⁻¹ (average±SE) in the deeper levels. The RGR calculated after 60 days was 115% in the shallower levels vs. about 60% in the deeper ones. A considerable decrease in growth rate was observed during the last period; this was probably due to the presence of increasing fouling community on the rearing cages surely affecting the light intensity.     

Feeding responses of juvenile shrimp Litopenaeus vannamei (Boone) fed at different frequencies under laboratory conditions

In shrimp farms, food partitioning during the course of the day is contradictory, ethology studies may help in determining the proper frequency. Litopenaeus vannamei juveniles were placed in 30 L aquariums (41 m⁻²), exposed to a 12:12 h light–dark cycle. Feeding was provided at 10% of biomass three, four and seven times per day, with observations made in 15 min h⁻¹ windows, initiated after the ration was offered. Latency to access the feeding tray and to start eating was recorded using instantaneous focal sampling and digestive tract filling (DTF) by the continuous focal method. Weight gain was recorded at the end of the experiment. We performed seven repetitions, with 28 individuals observed for 33 days for each treatment (490 h of observation). The three-times offering induced less latency for accessing the tray and for ingesting the feed as well as a higher DTF when compared with the other frequencies. Animals fed three and four times had similar weight gains, and were greater than those fed seven times. Our results indicate that a more spaced food offering stimulates the search for and ingestion of feed. As compared with other frequencies, the three-times-per-day option assumes lower labour costs and a more efficient use of the feed.     

Residual genetic variability in domesticated populations of the Pacific blue shrimp (Litopenaeus stylirostris) of New Caledonia,French Polynesia and Hawaii and some management recommendations

The Latin American shrimp Litopenaeus stylirostris was introduced in three different Pacific islands (Tahiti, New Caledonia via Tahiti, and Hawaii) and hatchery-propagated for 7–25 generations to develop shrimp farming based on these domesticated stocks. Three microsatellite markers have been used in an attempt to assess the genetic bases of the populations available to start a selective breeding program. The comparison of eight hatchery stocks (five New Caledonian, two Hawaiian and one Tahitian stocks) and one wild Ecuadorian population showed a much lower variability in the domesticated stocks than in the wild population, especially in New Caledonia and Tahiti (2–3.7 vs. 14–27 alleles per locus; 20–60% vs. 90% expected heterozygosity). The Tahitian and the New Caledonian stocks share the same alleles, suggesting that the loss of alleles occurred during the common past of these populations. On the contrary, New Caledonian and Hawaiian populations share only one common allele at the three loci studied. Although the low genetic variability and the resulting inbreeding of the New Caledonian stocks do not seem to affect their present performance, the results of this study demonstrate the usefulness of the introduction of new stocks in order to increase the potential responses to new controlled or uncontrolled selective pressures. The introduction in New Caledonia of the Hawaiian domesticated stocks, which would provide the local shrimp industry with 40% of the allelic diversity of the species, is advised and preferred to the one of wild animals in order to take advantage (i) of the spontaneous selection which occurred during domestication and (ii) of their favourable sanitary “specific pathogen free” status (no presence of four viruses: WSV, YHV, IHHNV, TSV) which limits the risk of introduction of pathogens.     

仿刺参与虾夷马粪海胆和菲律宾蛤仔混养效果的初步研究

水温13.8～20.0℃下,在容积50 L的塑料水槽中,放养体质量为(1.4±0.6)g的虾夷马粪海胆(Strongylocentrotus intermedius)11个,过量投喂海带(Laminaria japonica),再分别混养体质量为(3.4±0.6)g的仿刺参(Apostichopusjaponicus)0(A组)、3(B组)、5(C组)和10个(D组),体质量为(12.4±1.7)g的菲律宾蛤仔(Ruditapes philippim2rum)6个,排出水培养底栖硅藻和石纯(Ulva lactuca),用底栖硅藻饲喂仿刺参.77 d的饲养表明,仿刺参和海胆的成活率差异不显著(P>0.05),但混养组海胆的特定生长率(SGR)显著高于单养组(P<0.05),B、C和D组海胆的SGR分别比单养高9.12%、7.24%和10.06%,各混养组间差异不显著(P>0.05);混养海胆的饲料系数(7.28～7.70)分别显著低于单养(9.12)(P<0.05)组20.2%、15.5%和18.0%.将刺参的产量计算在内,B、C和D组海胆的饲料系数分别比对照组降低31.5%、26.8%和16.0%,但混养组间差异不显著(P>0.05).海胆和仿刺参的适宜混养比例为11:3.蛤仔和石纯生长慢,死亡率高.养殖排水培养的底栖硅藻以菱形藻(Nitzschia sp.)和卵形藻(Cocameissp.)为主,少量舟形藻(Navicula sp.).混养海胆性腺中亚麻酸、EPA DHA含量和n-3/n-6比值显著大于单养组(P<0.05),混养池水中氨氮含量低而稳,溶氧量高.     

Effect of partial and total replacement of fish, shrimp head, and soybean meals with red crab meal Pleuroncodes planipes (Stimpson) on growth of white shrimp Litopenaeus vannamei (Boone)

Red crab meal (RCM), as a potential protein source in diets for juvenile shrimp Litopenaeus vannamei, was evaluated over a 45‐day growth trial under laboratory conditions. Eight experimental diets were tested. The basal diet contained fish (tuna by‐product), shrimp head and soybean (solvent extracted) meals as primary protein sources. Fish or soybean meals were substituted, on an equal‐protein basis, at 33%, 66% and 100% by RCM, whereas shrimp head meal (SHM) was substituted at 100%. A commercial diet was included as a reference. Final weight ranged between 2.23 and 3.36 g and growth rates (GRs) between 0.048 and 0.073 g day⁻¹. Where 66% or 100% of the protein from fish or soybean meals was substituted by RCM, the diets produced significantly higher final weights and GRs than other diets. Regression analysis showed that final weight of shrimp depended significantly on the percentage of substitution, and that the maximum weight gain would be obtained when substituting RCM for 80.2% of fish meal and 81.2% of soybean meal. Feed conversion ratio was below 1.8 for all treatments and there was no apparent relationship with other aspects of the diet. Red crab meal served as a suitable protein source for partial or total replacement of tuna by‐product, soybean and SHMs for cultivated juvenile shrimp L. vannamei.     

Effect of stocking density on growth performance of juvenile sea cucumber Holothuria tubulosa (Gmelin, 1788)

Stock density is one among the most important factors in aquaculture that directly influences the growth of organisms; however, there is limited information about the effects of stocking density on growth performance of sea cucumber Holothuria tubulosa (Gmelin, 1788) that has a commercial potential and represents a new species for aquaculture. In this study, we investigated the effect of stocking densities on the growth performance of juvenile H. tubulosa (40.3 ± 3.34 g) in laboratory conditions. Stocking densities were selected as 6, 15 and 30 ind m^?2 with total biomass 253.3 ± 0.18, 601.2 ± 0.11 and 1201.4 ± 0.15 g m^?2 respectively. We monitored the growth by wet weights and calculated the growth performance through weight gain, growth rate, specific growth rate, relative weight gain, coefficients of variation and survival rate during 8 weeks of research period. We found that individual mean weight gain in 6 ind m^?2 group was approximately 29.53 g while it was 3.03 g and ?4.36 g for 15 ind and 30 ind m^?2 groups respectively. Results have shown that the specific growth rate tends to decrease as the number of individuals in unit area increases. The final mean weight, growth rate, specific growth rate, relative weight gain and coefficients of variation were significantly different among treatment groups. In conclusion, a density of 6 ind m^?2 is recommended for stocking juvenile H. tubulosa under rearing conditions. Stocking density of 15 ind m^?2 is not favourable for long term as the growth rate is negligible where 30 ind m^?2 should be avoided in tank‐based rearing units.     

Is it possible to raise,offspring of the 25th generation of Litopenaeus vannamei (Boone) and 18th generation Litopenaeus stylirostris (Stimpson) in clear water to 40 g?

Peneid shrimp are commonly reared in clear‐water aquaria or tanks for short‐term studies of 4–6 weeks during controlled experiments, such as nutrition studies to estimate dietary nutrient requirements. Recently, in line with the genetic program at Centre Océanologique du Pacifique (COP), experimental clear‐water facilities were tested for the first time over a longer rearing period. Environmental conditions used to maintain animal growth in clear‐water system using a well‐balanced diet were defined. After 100 days, shrimp growth rates tended to decrease and only by adjusting the diet could shrimp complete their life cycle and reach maturation size of around 40 g. This paper presents information on stocking density, diet quality and husbandry linked to reproduction that must be considered to successfully rear animals from PL's to breeder size in clear water. By following these protocols a minimum amount of breeders can be used to meet production goals. Moreover, by isolating a small group of individuals, genetic diversity can be preserved, thereby allowing specific crosses for selective breeding purposes. Length of trials, amount of feed, composition of feed, growth performances and maturation success are reported and should encourage further studies to optimize rearing conditions in clear‐water rearing.     

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50–1.50 g L⁻¹). Diets 1–6 were formulated to contain 360 g kg⁻¹ crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9–19.0 g kg⁻¹ dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.48±0.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg⁻¹ or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg⁻¹ dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg⁻¹ dry diet (37.8 g kg⁻¹ dietary protein).     

低盐度条件下的凡纳滨对虾幼虾亮氨酸营养需求

为了探讨低盐度(0.6～0.8 g/L)条件下初始体质量为(0.38±0.004)g的凡纳滨对虾(Litopenaeus vannamei)幼虾的亮氨酸需求量,以鱼粉、花生麸和L-晶体氨基酸为蛋白源配制含粗蛋白400 g/kg的6种等氮饲料,标记为L7～L12组,各组亮氨酸水平分别为15.95、17.95、19.95、21.95、23.95和25.95 g/kg(饲料干物质).每组3个重复,每个重复30尾虾,进行56 d生长实验.结果表明,凡纳滨对虾幼虾的增重率随饲料亮氨酸水平的升高而升高,当亮氨酸水平达到23.95 g/kg(L11组)时,增重率达到最高值(1143.11±36.40)％,显著高于L7组(P＜0.05);亮氨酸水平继续提高,增重率变化不显著(P＞0.05).幼虾的蛋白质效率、全虾体蛋白沉积率和血淋巴总蛋白随着饲料亮氨酸水平的升高呈现升高趋势,最高值出现在L11组,并显著高于L7组(P＜0.05).各实验组饵料系数、血淋巴谷丙转氨酶、谷草转氨酶活性和尿素氮含量则呈现降低的趋势,最低值出现在L11组,且显著低于L7组(P＜0.05).以增重率为指标,根据折线模型可知,低盐度条件下凡纳滨对虾幼虾的亮氨酸最适需要量为24.80 g/kg饲料,即61.99 g/kg饲料蛋白.     

Effects of light intensity on daily activity rhythm of juvenile sea cucumber,Apostichopus japonicus (Selenka)

Eight light‐intensity treatments (natural light, continuous darkness, and 15, 30, 60, 125, 250 and 500 lx under LD 12:12 cycle) were used to investigate the effects of light intensity on the daily activity of 30.27±3.08 g sea cucumber Apostichopus japonicus (Selenka). Cyclic nocturnal activity patterns of behaviour were observed at different light intensities in the range of 15–500 lx under LD 12:12 cycle. And an ongoing nocturnal cycle persisted in DD cycle for up to 8 days, but longer feeding time and less marked rhythm occurred at continuous darkness. Under poor light conditions (I<5.18 lx), the daily activity rhythm of A. japonicus was governed by an innate biological clock and the effect of light intensity was not significant among different treatments. And more individuals tended to retreat to shelters (from 56.04% to 91.83%) with the increase of light intensity within the weak light condition (from 5.18 to 278 lx). However, the daily behaviours of A. japonicus were influenced under strong light conditions (>278 lx). Less than 8.17% individuals kept actively feeding and the proportion was not decreased with the increase of light intensity.     

Quantitative dietary leucine requirement of juvenile Pacific white shrimp,Litopenaeus vannamei (Boone) reared in low‐salinity water

The experiment was conducted to determine the leucine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low‐salinity water (0.50–1.20 g L^?1). Six diets were formulated to contain 410 g kg^?1 crude protein with fish meal, peanut meal and precoated crystalline amino acids with different concentration of l ‐leucine (16.72, 19.60, 22.06, 24.79, 27.28 and 30.16 g kg^?1 dry diet). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.38 ± 0.002 g), and the feed trial lasted for 8 weeks. The results indicated that the maximum weight gain was observed at 24.95 g kg^?1 dietary leucine group, whereas the diets containing higher leucine concentration conversely reduced the growth performance (P < 0.05). Moreover, the highest body protein content and body protein deposition and the lowest haemolymph AST and ALT activities were also found at 24.95 g kg^?1 dietary leucine group. With the increase in leucine in diets, a dose‐dependent increase was found in body lipid content and haemolymph urea concentration. The polynomial regression calculated using weight gain, feed efficiency and body protein deposition indicated that the optimal dietary leucine requirement for L. vannamei reared in low‐salinity water was 23.73 g kg^?1 leucine of dry diet, correspondingly 57.88 g kg^?1 of dietary protein.     

Effect of substitution of shrimp meal, fish meal and soy meal with red crab Pleuroncodes planipes (Stimpson) meal in pelleted diets for postlarvae and juvenile Farfantepenaeus californiensis (Holmes)

A study was conducted to investigate red crab Pleuroncodes planipes (Stimpson) as a protein source in experimental diets for postlarvae and juvenile brown shrimp Farfantepenaeus californiensis (Holmes). Four experimental diets were prepared. The base diet contained 10% shrimp meal, 25% fish meal and 27% soy meal plus other ingredients. Complete substitution of shrimp meal with red crab meal (RCM) was done on the remaining diets. Additionally, 5% of the soy meal was replaced with RCM in one diet, and 4% of the fish meal was replaced with RCM in the last diet. A commercial diet (36% crude protein) was used as an external comparison diet to provide a basis to evaluate the growth of shrimp on the test diets. The trial with shrimp postlarvae showed that diets containing RCM produced better results in terms of final weight (3.24–3.55 g), growth rate (0.044–0.046 g d^?1) and feed conversion ratio (FCR) (3.7–3.8) than the base or the commercial comparison diets. The FCR was significantly different between the base diet (4.5) and the commercial diet (5.5). Final weight (3.83 g) and growth rate (0.044 g d^?1) were higher when the diet replacing 4% fish meal was used to feed juveniles. The commercial diet produced the lowest values of final weight (2.57 g) and growth rate (0.025 g d^?1) and the highest FCR (5.6) (P<0.05). These results indicate that the use of P. planipes as a replacement for traditional ingredients in shrimp rations is desirable.