Effects of starvation and feeding on blood chemistry,fatty acid composition and expression of vitellogenin and fatty acid-binding protein genes in female swimming crab <Emphasis Type="Italic">Portunus trituberculatus</Emphasis> broodstock

Portunus trituberculatus broodstock were stocked in plastic tanks to evaluate the effects of starvation and feeding on gonadal development, blood chemistry, fatty acid composition, and expression of vitellogenin (Vtg) and fatty acid-binding protein genes (FABP) in females. Two treatments (starved and fed) were randomly assigned to triplicate groups of 90 swimming crab broodstock (approximately 230 ± 45 g). In the starved treatment, crabs were starved for 30 days, whereas in the fed treatment crabs were fed once a day with clams. The gonadosomatic index decreased significantly in starved crabs (P < 0.05), as did the serum glucose and cholesterol concentrations; conversely, the total protein concentration in serum significantly increased (P < 0.05). In the ovary, there was a significant relative decline of 18:0, 16:1n-7 and 20:1n-9 fatty acids and relative increases of 20:4n-6, 22:6n-3, 18:1n-9 and 20:5n-3 in starved crabs compared to fed crabs (P < 0.05). Relative expression of Vtg in the ovary decreased significantly in starved crabs (P < 0.05), while there was no significant difference in hepatopancreas Vtg expression between starved and fed crabs (P > 0.05). Starvation suppressed gonadal development in female swimming crab broodstock.     

Effect of dietary protein level on fattening and mineral profiles of mud crab,Scylla serrata,in individual cages under mangrove ecosystem

A fattening demonstration was carried out in Sorlagondi (15.8640⁰N, 80.9671⁰E) mangrove ecosystem in Diviseema region, Krishna district, Andhra Pradesh, India, by adapting a holistic approach of “Integrated Mangrove Fishery Farming System.” The local Yanadi tribal communities engaged in mangrove afforestation programmes were provided with 144 individual crab fattening cages (60 × 40 × 30 cm). Two formulated feeds were prepared with two levels of protein (32% and 36%) and were tested on fattening of the marketable size (200–1,000 g) of mud crabs, Scylla serrata. Significantly (p < 0.05) higher weight gain, feed and protein efficiency measures were observed in crabs fed with CP‐36% diet across all size groups. This diet also reduced the time (days) taken for fattening crabs irrespective of the size. Moisture content was very high in soft crabs (>800 g/kg) compared with hard crabs (679.70–688.65 g/kg), whereas the reverse trend was observed for protein, ether extract and ash content. Both diet and size of the crab have not shown much influence on proximate composition. However, cultured hard crabs had higher ether extract (20.10 g/kg) than wild hard crabs (17.06 g/kg). The changes in concentration of mineral values on wet basis indicated the increase in concentration in hard crabs compared with soft crabs, whereas when the percentage change, values on dry matter basis indicated the reduction in concentration of mineral contents of K, Na, P, Cu, Fe and Zn. This higher concentration of minerals in soft crabs could possibly be attributed to the reabsorption of minerals into soft muscle or to the body fluids.     

Does the wild‐caught Chinese mitten crab megalopae perform better than the hatchery‐produced seed during the juvenile culture?

Although wild Yangtze Eriocheir sinensis juveniles (coin‐sized seed) have better culture performance than the pond‐reared juveniles during the adult crab culture stage, the culture performance of wild‐caught megalopae (WC) remains unknown. Therefore, this study was designed to compare the growth, survival rate, crab yield, feed conversion rate (FCR), precocity, final weight and size distribution between WC and hatchery‐produced megalopae (HP) during the juvenile culture stage. Wild‐caught megalopae had significantly higher body weight, weight gain rate (WGR) and specific growth rate (SGR) during 0–4 weeks but lower WGR and SGR than HP during 4–8 weeks (p < .05). Although WC had a significantly lower survival rate and yield of normal juvenile crabs than HP, total yields of normal juveniles and precocious crabs were similar. Wild‐caught megalopae had a significantly higher precocious rate and yield of precocious crabs than HP (p < .05). Regardless of sex, no significant differences were found in the gonadosomatic index (GSI), hepatosomatic index (HSI) and final weight of normal juveniles and precocious crabs between WC and HP. As for the size distribution of normal crabs, WC had a higher percentage of small female juveniles (<3 g) but a lower proportion of middle size ranges (3–5.99 g and 6–8.99 g) than HP for females (p < .05), and there was no significant difference for males. In conclusion, wild megalopae of the Yangtze E. sinensis had worse culture performance than the hatchery‐produced seeds; therefore, wild megalopae would not be recommended for commercially juvenile culture of E. sinensis.     

Individual growth pattern of juvenile stages of the Chinese mitten crab (<Emphasis Type="Italic">Eriocheir sinensis</Emphasis>) reared under laboratory conditions

The specific growth pattern of Chinese mitten crab, Eriocheir sinensis, during the juvenile stages was investigated under an individual rearing system for 160 days, including parent crab selection, hatchery management, larval stages, and juvenile cultivation. There were 36 males and 40 females developed from megalopa to the juvenile crab stage 10 (M–C10), with a total survival of 38%. The survival rate in early stages (M–C3) remained less than 80%, which was lower than that in latter stages (>?90%). The intermoult duration sharply increased in an exponential manner (y?=?3.1059e^0.2149x R²?=?0.9383) from 4?±?0.54 days to 38?±?6.26 days. The increments in wet weight, carapace width, and carapace length per moult were recorded throughout the experiment, which followed certain patterns with progressing moulting time. In addition, moulting increment in wet weight varied greatly from C1 to C6, with a minimum increment of 108.09%. Meanwhile, the specific growth rate markedly increased in the early stages and subsequently decreased, mainly because of significant increases in the intermoult duration starting from C6 stage. Males and females could be differentiated at C4 based on sexual dimorphism in the abdomen, and the most distinct changes in female and male juvenile crabs occurred in the shape of the abdomen and amount of cheliped fluff, respectively.     

Induction of moulting in hatchery‐reared mangrove crab Scylla serrata juveniles through temperature manipulation or autotomy

The effects of temperature and autotomy of chelipeds on survival, growth and moulting of mangrove crab (Scylla serrata) juveniles were investigated under laboratory conditions for 60 days. Hatchery‐produced crabs with 2.0–2.3 cm internal carapace width (1.7–2.2 g body weight) at intermoult stage were exposed to one of four temperature treatments (constant 29, 32 or 35°C, or ambient [24–31°C]) or subjected to cheliped autotomy. All crabs held at 35°C had 100% mortality due to incomplete moulting during first moult. The mean survival of crabs at termination was 58%, 64% and 50% for ambient temperature, 29 and 32°C respectively. Specific growth rate (SGR) of crabs in the ambient and 29°C were comparable but significantly lower than those at 32°C. The moult interval of the crabs was significantly shorter in treatments with constant water temperature of 29 and 32°C compared with ambient temperature. The survival of crabs with intact chelipeds was comparable with those with one or two autotomized chelipeds. Crabs with intact or one autotomized chelipeds had significantly higher SGR than crabs with both chelipeds autotomized in the first moult. On the second moult, however, high SGR was observed in crabs with two chelipeds autotomized. The moult interval was significantly shorter in the autotomized crabs compared with crabs with intact chelipeds. The results suggest that the optimum water temperature for rearing S. serrata juveniles ranges from 29 to 32°C. Likewise, autotomy of chelipeds can promote moulting without adversely affecting survival of crabs.     

The Effect of Depuration on Metals,Bacteria, and Nutrition in Venus verrucosa from the Aegean Sea: Benefit and Risk for Consumer Health of Warty Venus

ABSTRACT

In this study, the effect of the depuration period on proximate composition, metals, fatty acids, and bacteria in the edible tissue of warty venus (Venus verrucosa) collected from ?zmir Bay in the Aegean Sea was investigated. In addition, benefit and risk for human health associated with the consumption of warty venus were determined by atherogenic index (AI), thrombogenic index (TI), polyene index (PI), fish lipid quality (FLQ), target hazard quotient (THQ), and hazard index (HI). The depuration process did not show a significant (P > .05) effect on proximate composition, except for ash. The depuration process was successful in reducing bacteria growth and the concentrations of all metals, except for copper. Total aerobic mesophilic bacteria count of 1.94 log CFU/g in the fresh samples was uncountable at 24 h of depuration. The concentrations of cadmium, lead, copper, iron, and zinc were below the limit values allowed for safe consumption. The analyzed metals were safe for human consumption based on provisional tolerable weekly intake (PTWI), THQ, and HI. Significant variations were also observed in the fatty acid values depending on the depuration periods (P < .05). The n3/n6 and polyunsaturated/saturated fatty acid ratios were greater than those recommended by the FAO/WHO. Moreover, the AI and TI of samples were under established limits.     

Dietary phospholipids requirement of the early juvenile (C1) swimming crab,Portunus trituberculatus

A 30‐day experiment was conducted to investigate the effect of phospholipids (PLs) on growth performance, survival, fatty acid profile and gene expression of the early juvenile (C1) swimming crab (Portunus trituberculatus). Five semi‐purified diets were formulated with graded PLs levels (0%, 1%, 2%, 4% and 8%). Each diet was fed to four replicates of crabs (30 crabs per replicate, initial weight: 8.4 ± 0.1 mg). In this study, crabs fed diets with 2%, 4% and 8% PLs had significantly higher survival rates than crabs fed with 0% and 1% PLs. Crabs fed diets with 0% and 1% PLs had significant lower weight gain (WG) than crabs fed with 8% PLs. But crabs fed with diets containing 2%, 4% and 8% PLs showed no significant difference in WG. Besides, the content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in whole body was higher than that in diets, but the monounsaturated fatty acids (MUFA) content showed an opposite trend. The EPA and DHA content in whole body increased with the increase in dietary PLs. Moreover, the moulting number increased with the increasing dietary PLs levels, the lowest moulting number was observed in crabs fed diets without supplementation of PLs. The ecdysteroid receptor (EcR) was found to be significantly up‐regulated by PLs levels. This study demonstrated that 2% PLs could meet the requirement of early juvenile (C1) swimming crab based on the growth and survival. And 4%–8% PLs supplemented in diets could reduce the leaching of feed.     

Quality improvement by feeding wild-caught edible crab (Cancer pagurus L.): a pilot study

High season for the Norwegian Brown crab fishery (Cancer pagurus L.) is from August to October when meat yield (MY) is high, especially for female crabs. However, the quality of hard‐shelled crabs may vary between and within regions also, at this time of the year. A pilot study was conducted to examine whether feeding could increase MY in wild‐caught medium‐quality females caught during four periods from July to November. Feed intake was compared for crabs fed at different temperatures (3, 5, 8, 10 and 12°C). The crabs were fed three times a week in periods from 15 to 20 days. Feed intake increased with temperatures. Quality, as assessed by MY, was higher for all fed groups compared with reference groups. A clear pattern in quality improvement was seen according to season. Hepatosomatic index increased more than the gonadosomatic in July, slightly more in August, while gonadosomatic development was higher in September. In October, some spawning occurred. The result indicates that feeding had a positive effect, which seemed to increase with increasing temperature. We suggest that the temperature should be at least 12°C in order to achieve an optimal gain in MY when the feeding period is 3 weeks.     

Comparison of nonvolatile taste active compounds of wild and cultured mud crab <Emphasis Type="Italic">Scylla paramamosain</Emphasis>

Nonvolatile taste active compounds, including free amino acids (FAAs), 5′-nucleotides, betaine, soluble sugars, trimethylamine oxide and organic acids of wild and cultured mud crab Scylla paramamosain were examined. The main taste in mud crab (MC) is derived from the FAAs, 5′-nucleotides, betaine, and organic acids, based on the fact that these compounds have a taste activity value (TAV)?>?1. Wild MCs had a higher content of total FAAs, 5′-nucleotides, betaine, and organic acids in meat compared with cultured animals. However, no differences in the taste active compound levels were observed in the gonads of wild and cultured MCs, with betaine being the exception (wild crab?>?cultured crab). The total concentrations of FAAs in MC ranged from 12.71 to 36.94 mg/g. Monosodium glutamate (MSG)-like FAAs were primarily contributed by glutamic acid, and ranged from 0.71 to 0.93 mg/g. The concentrations of 5′-nucleotides were 1.10–2.24 mg/g, in which 5′-inosine monophosphate (IMP) and 5′-adenosine monophosphate (AMP) were the predominant TAVs (TAV?>?1). The total concentrations of organic acids in MC were 2.41–11.10 mg/g, in which lactic and succinic acid in meat, and citric acid and succinic acid in female gonads were the main organic acids. The gonads were observed to have higher concentrations of 5′-nucleotides and organic acids compared with crab meat, with the equivalent umami concentration in gonads being higher than that in crab meat. In conclusion, wild MCs contained more active-taste nonvolatile flavor components relative to those detected in cultured MCs.     

Biochemical and Microbiological Assessment of Crucifix Crab (Charybdis feriatus) Stored at 4°C

Charybdis feriatus is a highly prized crab in the local and international markets of East Asian countries. In local markets, crabs are sold live, iced, or refrigerated at 2°C – 4°C. The present study was carried out to determine the shelf life of whole crab stored at 4°C for 192 h using a set of biochemical, microbiological, and sensorial parameters. Biochemical indicators such as the total volatile base nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) increased significantly during storage and within an acceptable limit up to 144 h. Regarding the biogenic amines, cadaverine and spermidine increased significantly (p < 0.05) during the storage period. Among them, cadaverine could be proposed as a useful spoilage indicator for this crab species. The mesophilic and psychotropic bacterial count exceeded the limit of acceptance after 144 h of storage. Sensory attributes were gradually diminished with the storage time. Sensory scores were found to correlate well with both mesophiles and psychrotrophs. Based on the results of this study, the meat quality of Charybdis feriatus can be maintained up to 144 h when properly stored at a temperature of 4°C ± 1°C.     

Effects of various levels of dietary protein on survival,molting frequency and growth of juvenile blue crabs (Callinectes sapidus)

An 18-week study was conducted to examine growth characteristics of the juvenile blue crab (Callinectes sapidus Rathbun) fed various levels of dietary protein. Hatchery raised individuals (157) of identical age (160 days) from the same gravid female were assigned to one of four dietary treatments: adult brine shrimp (Artemia salina Leach) and artificial pelleted diets containing crude protein levels of 23, 37, and 49%.Growth rate, measured as a function of mean weight and mean carapace width, indicated that brine shrimp-fed crabs were larger (P < 0.05) than crabs fed artificial pelleted diets. Also, blue crabs fed either 37 or 49% crude protein were larger than crabs fed the 23% crude protein diet. Molting frequency was greater in the brine shrimp-fed crabs than in those fed the artificial diets. No differences in growth were detected when comparing males vs. females fed the artificial diets. However, females demonstrated greater growth than males within the brine shrimp treatment. Protein concentration of freeze-dried whole blue crab carcasses was greater in brine shrimp-fed crabs than in crabs fed the artificial pelleted diets (P < 0.05).     

Ghost fishing in the pot fishery for blue swimmer crabs Portunus pelagicus in Queensland,Australia

Blue swimmer crabs (Portunus pelagicus) are an economically important crab caught in baited traps throughout the Indo-west Pacific and Mediterranean. In Australia they are traditionally caught using rigid wire traps (≈pots) but there has been a recent increase in the use of collapsible pots constructed from polyethylene trawl mesh. Two experiments were conducted in Moreton Bay, Queensland, to determine the ghost fishing potential of lost crab pots on both target and bycatch species and to evaluate the differences between traditional and contemporary pot designs. A lost contemporary, collapsible trawl mesh pot will catch between 3 and 223 P. pelagicus per year after the bait has been exhausted, while a traditional wire mesh pot would catch 11–74 crabs per year. As most fishers now use the collapsible trawl mesh pots, ghost fishing mortality could be as high as 111,811–670,866 crabs per year. Bycatch retention was also higher in contemporary designs. Periods of strong winds appeared to increase the ghost fishing potential of lost pots. The use of escape gaps, larger mesh sizes and construction options that allow for the deterioration of entrance funnels to minimise ghost fishing are recommended to reduce environmental impacts.     

Effect of dietary lipid levels on growth performance,fatty acid profile and enzymatic activity of juvenile swimming crab,Portunus trituberculatus

The main objective of this investigation was to study the lipid requirements of the early juvenile (C1) swimming crab (Portunus trituberculatus) based on growth performance, survival, moulting and fatty acid profile. Four test diets were formulated with graded lipid levels (3.63%, 6.70%, 10.72% and 13.91%). Each diet was fed to 4 replicates of crabs (30 crabs per replicate initial weight (8.4 ± 0.1 mg). In this study, crabs fed diets with 13.91% lipid had significantly (p < 0.05) higher survival than crabs fed with 3.63% lipid, but no significant (p > 0.05) improvement of survival was observed when dietary lipid increase from 6.70% to 13.91%. Crabs fed diets with 10.72% and 13.91% lipid had significant higher weight gain(WG) than crabs fed with 3.63% lipid. While crabs fed with diets containing 6.70%, 10.72% and 13.91% lipid showed no significant (p > 0.05) difference in weight gain(WG). Moreover, the lowest moulting number was observed in crabs fed diets with 3.63% lipid, but there was no significant difference (p > 0.05) among other groups. The content of LC‐PUFA and DHA in the crabs fed diets with 3.63% lipid was significant (p < 0.05) lower compared to other groups. But there was no significant (p > 0.05) difference in EPA and ARA content among all groups. The activity of lipase increased as dietary lipid level increased (from 6.70% to 10.72%). However, beyond 10.72%, a significant (p < 0.05) decreased in lipase activity was observed. The regression analysis of weight gain data indicated that crab fed diet containing 10.47% lipid level is considered as optimum lipid level for its maximum growth and moulting process.     

山东半岛南部近岸海域蟹类群落结构特征

根据使用单船底拖网进行2014年8月和10月、2015年2月和5月4个航次的调查数据,对山东半岛南部近岸海域蟹类种类组成、时空分布、优势种、物种多样性等群落结构特征进行了研究。结果显示,4次调查共捕获蟹类15种,隶属于7科12属,其中三疣梭子蟹(Portunus trituberculatus)、日本蟳(Charybdis japonica)是主要经济种类,其余多为小型饵料型蟹类;双斑蟳(C.bimaculata)在4个季节中皆为优势种,三疣梭子蟹在8月和10月航次为优势种,优势种季节更替明显;生物量季节变化明显,春季时较低,在夏季达到峰值,夏季到冬季呈降低趋势;蟹类群落物种多样性指数(H′)变化范围为0.32~0.53,均匀度指数(J′)变化范围为0.23~0.37,丰富度指数(D)变化范围为0.32~0.55,其中物种多样性指数与丰富度指数季节变化明显,均匀度指数季节变化不明显;多元统计分析结果表明,山东半岛南部近岸海域4季节蟹类群落结构均可以划分为西南部海域组、东北部远岸海域组和西北部近岸海域组3个组群,季节间组群站位组成变化明显,群落结构不稳定。研究表明:1)山东半岛南部近岸海域蟹类以小型饵料型蟹类为主,蟹类多样性水平较低,优势种更替明显,蟹类群落不稳定;2)山东半岛南部近岸海域蟹类群落划分较为明显,特征种主要为双斑蟳、泥脚隆背蟹(Carcinoplax vestita)等小型饵料型蟹类。     

Cottonseed meal protein hydrolysate stimulates feed intake and appetite in Chinese mitten crab,Eriocheir sinensis

One hundred and twenty crabs (initial weight: 51.32 ± 0.06 g) were fed three experimental diets with cottonseed meal protein hydrolysate (CPH) at 0, 6 and 12 g/kg for 60 days. The results showed that CPH0.6 diet significantly improved the 1‐hr feed intake, protease activity and weight gain of crabs. In thoracic ganglia, 4E‐binding protein (4E‐BP) expression level of crab fed the diets containing CPH was significantly higher than CPH0 group. In cerebral ganglia, protein kinase B and 4E‐BP expression levels of crab fed CPH0.6 diets were significantly lower than CPH0 group. In mid‐intestine, target of rapamycin (TOR) relative expression level of crabs fed the diets containing CPH was significantly lower than CPH0 group. 4E‐BP expression level showed an opposite pattern. In thoracic ganglia, cerebral ganglia and mid‐intestine, leptin receptor expression level of crabs fed CPH0.6 diet was significantly lower than CPH0 group. Neuropeptide Y and neuropeptide Y receptor expression level of crab fed CPH0.6 diet was significantly higher than CPH0 group. In conclusion, our results indicated that dietary supplementation of 6 g/kg CPH could stimulate appetite and quicken feeding rate via the TOR signalling pathway.     

Effect of different forms of Artemia biomass as a food source on survival,molting and growth rate of mud crab (Scylla paramamosain)

An experiment was conducted to evaluate the effect of different forms of Artemia biomass as a food source on survival, molting and growth rate of mud crab Scylla paramamosain. Instar 1 crablets with a mean weight of 0.0082 ± 0.0007 g were reared both individually and communally and fed with different diets consisting of fresh shrimp meat (control feed), live Artemia biomass, frozen Artemia biomass and a dried Artemia‐based formulated feed for 40 days. The highest survival was obtained for crablets receiving live Artemia (92.5% and 75.8%) followed by the groups fed with frozen biomass (90.0% and 47.5%), the control feed (72.5% and 24.2%) and the dried Artemia‐based diet (60.0% and 21.7%) for individual and communal cultures, respectively. The intermolt period, the total number of moltings and the growth rate, which were determined on individually reared crabs, showed the same pattern as for survival. The results suggest that crab performance decreased in the following order: live Artemia>frozen Artemia > fresh shrimp meat > dried Artemia‐based formulated feed. Live Artemia biomass proved an ideal feed for nursery of Scylla paramamosain crabs. Frozen Artemia biomass may be an alternative in times of shortage. Our findings illustrate the high potential for local utilization of Artemia biomass in Vietnam for reliable production of mud crab juveniles.     

不同养殖水域中华绒螯蟹滋味差异分析

本研究分析不同水域中华绒螯蟹(Eriocheirsinensis)可食率和滋味差异,以期为挖掘消费者不同偏好性的内在原因提供参考.选取阳澄湖、固城湖、太湖和兴化大闸蟹为研究对象,测定可食率、整体滋味轮廓、滋味相关指标.结果显示,太湖蟹可食率最高,雄蟹为(33.08±0.31)％,雌蟹为(37.65±1.09)％;在整体...     

Size at sexual maturity and body size composition of mud crabs <Emphasis Type="Italic">Scylla</Emphasis> spp. caught in Don Sak,Bandon Bay,Gulf of Thailand

Size at sexual maturity and body size composition of mud crabs Scylla spp. were examined as the basis for settling a minimum landing size as a fishing regulation in Don Sak, Bandon Bay, Gulf of Thailand, which has suffered serious mangrove habitat degradation. Mud crabs were caught using baited traps and gill nets. Hooked metal rods were also used to lever the crabs out of their burrows inside the mangroves. Two mud crab species, S. paramamosain and S. olivacea, occur in the bay; S. paramamosain is the dominant species, accounting for 87% of the samples. The size at which 50% of the S. paramamosain females reached maturity (SM₅₀) was estimated as an external carapace width (ECW) of 112.0 mm based on the morphology of the abdomen. Allometric changes in the crushing chelae height to ECW ratio suggested that the SM₅₀ of S. paramamosain males occurred at 106.4 mm ECW. The body size composition revealed that mainly immature mud crabs were exploited in Don Sak. To maintain a sustainable fishery for mud crabs, fishing regulations—including a minimum landing size based on the SM₅₀ estimates—are essential, as is habitat restoration.     

Evaluation of limb autotomy as a promising strategy to improve production performances of mud crab (Scylla olivacea) in the soft‐shell farming system

Soft‐shell crab, a newly moulted crab having non‐calcified and hydrated soft exoskeleton, farming has been increasing tremendously in recent years throughout the world due to its high market price and consumer preferences. However, high aggressiveness and cannibalistic behaviour of mud crab limit its culture to an individual chamber system which ultimately makes the soft‐shell mud crab farming space and labour‐intensive. Therefore, the aim of this study was to improve the efficiency of soft‐shell crab production by autotomy of the claw and/or walking legs to reduce the moulting duration and intensify the culture system through double stocking in the existing individual chamber culture system. To achieve our objectives, a series of experiment were conducted at both indoor and on‐farm levels by removing the claw and/or walking legs of Scylla olivacea for two consecutive moulting cycles. Results showed that both claw ablation significantly (p < .01) shortened the moulting duration and increased the carapace width, weight gain, specific growth rate, feeding efficiency and yield parameter compared to the non‐ablated crabs more prominently at 1st moulting than the 2nd moulting in both indoor and on‐farm trials. Ablation of all walking legs while keeping the claw intact did not significantly influence (p > .05) the moulting duration and carapace width, but significantly (p < .01) improved the specific growth rate, weight gain, feeding efficiency and yield parameters at 1st moulting compared to the non‐ablation and unilateral three walking leg ablation groups. However, ablation of all appendages (both claw and walking legs) showed significant (p < .01) improvements of carapace width, weight gain, specific growth rate, feeding efficiency and yield parameters, and shortened the moulting duration up to 23 days from 34 days during 1st moulting and up to 27 days from 40 days at 2nd moulting. The survivals of different autotomized mud crabs were statistically non‐significant (p > .05) to the non‐autotomized crabs in various indoor and on‐farm trials. Besides improving the production performances, ablation of bilateral claw and all appendages allowed to double the stocking density in the existing individual chamber‐based soft‐shell crab farming that enhanced the production about threefold higher than the existing individual chamber‐based culture system. Finally, our results suggest that autotomy could be a promising technology for the commercial farming of soft‐shell mud crab in near future.     

Broodstock management and the potential to improve the exploitation of mangrove crabs, Scylla serrata (Forskål), through pond fattening in Ranong, Thailand

Abstract Mangrove crabs, Scylla serrata (Forskål), represent one of the main economic resources in the Ranong mangrove ecosystem on the Andaman Sea cost of southern Thailand. However, there is a serious problem of overfishing which has caused fishermen increasingly to sell undersized crabs to meet market demand and maintain their income levels. The crab population and fishing activities were studied to assess the scope for better management of the fishery, especially protection of female broodstock, and the feasibility of using young crabs for aquaculture. Berried crabs examined were always larger than 10·0cm (carapace width), with the great majority of females maturing in the size range 10·0–11·5cm. Gonosomatic index values peak in September, within a main egg carrying and spawning period from July to December. Protecting female crabs from fishing pressure during this season, plus limits on the harvesting of crabs less than 10cm, or using them for fattening in ponds, could lead to better utilization of this resource. Crab farming in Ranong is constrained by climatic factors, the presence of acid-sulphate soils and lack of technical knowledge among the local fishermen. An attempt initially to culture crabs from Ranong under more favourable conditions at Surat Thani showed limited success. Nonetheless, there is a considerable price differential between wild and pond-fattened crabs to encourage further interest in crab farming in Ranong.