Survival Of Crab Research Articles

Dietary supplementation of Roseovarius litoreus improves survival and immune defense of the swimming crab Portunus trituberculatus

The aquaculture of the swimming crab Portunus trituberculatus is challenged by vibriosis, and Rhodobacteraceae strains play a crucial role in maintaining gut health and enhancing the immunity of crustaceans. In this study, we investigated the effects of dietary supplementation of Roseovarius litoreus, a member of Rhodobacteraceae, on the survival and immune defense of the swimming crab. The results showed that 60-day dietary supplementation of R. litoreus resulted in a marked increase in the mRNA expression of gut ZO-1. Meanwhile, R. litoreus increased zero-radius operational taxonomic unit (ZOTU) richness and changed the gut bacterial community, which was manifested by the enriched Carboxylicivirga and Roseovarius and depleted Photobacterium and Vibrio, thereby upregulating functional potentials of the gut bacterial community in the immune system and biosynthesis of other secondary metabolites. After a 72-h V. parahaemolyticus challenge, R. litoreus-supplemented crabs had an increased survival rate, reduced histological damage of hepatopancreas and gut, and improved expressions of immune-related genes and lysozyme activity. Moreover, R. litoreus-supplemented crab gut still harbored more Carboxylicivirga and Roseovarius but had fewer Vibrio gene copies than control crabs, which led to similar changes in functional potentials. Notably, all ZOTUs that were positively correlated with immune-related genes and lysozyme activity belonged to Bacteroidetes, Bacteroidales, or Carboxylicivirga. Taken together, we highlight the probiotic role of R. litoreus in the survival and immune defense of the swimming crab. These findings may contribute to the development of indigenous bacteria of the swimming crab as potential probiotics for the control of vibriosis.

Examination of role of the AMP-activated protein kinase (Ampk) signaling pathway during low salinity adaptation in the mud crab, Scylla paramamosain, with reference to glucolipid metabolism

It is known that the marine euryhaline crab, mud crab (Scylla paramamosain), is capable of adapting to low salinity conditions through an innate osmoregulatory system. However, the influence of nutritional conditions during low salinity adaptation has not been fully elucidated. In this study, transcriptome analysis was employed to examine whether low salinity affects the AMP-activated protein kinase (Ampk) signaling pathway, and thereby carbohydrate and lipid metabolism. Further analysis revealed that low salinity activated the expression of P-Ampk and promoted glycolysis and lipolysis, which enhances glycogen and lipid utilization. Nutritional deprivation confirmed that nutrients influenced the survival and osmotic pressure regulation of mud crab under to low salinity via the Ampk signaling pathway. During adaptation to low salinity, carbohydrates were the primary energy source in the initial 7 days, followed by lipids. Further investigation showed that pharmacological stimulation of mechanistic targets in the Ampk signaling pathway using metformin could promote the osmotic pressure regulation of mud crab, confirmed the pivotal role of this pathway in low salinity adaptation. Overall, the present study demonstrated that nutrition, metabolism and osmotic pressure regulation interactively contribute to salinity adaptation in mud crab. Specifically, low salinity induced remodeling of nutritional metabolism homeostasis and promoted glycolipid catabolism, thereby providing energy for osmotic pressure regulation in mud crabs.

Effects of background color on survival, growth, and shell coloration of juvenile Chinese mitten crab (Eriocheir sinensis)

Background color is a crucial factor influencing the growth performance and feed utilization in crustaceans. However, little is known about its impacts on the culture performance of Chinese mitten crab (Eriocheir sinensis). In this study, we examined the impacts of six different background colors (white-W, black-BK, green-G, red-R, yellow-Y, and blue-BL) on growth, inter-molt period, and coloration and total carotenoids content of carapace of juvenile E. sinensis. The culture experiment comprised two trials: a 68-day individual culture, and a 30-day group culture. Individual culture results: No significant effects of background color were found on weight gain rate (WGR), specific growth rate (SGR), molting interval, carapace length and width, and survival rate (SR) of the juvenile crabs (P > 0.05). However, during the second molting cycle, the BL group exhibited the highest WGR, and the G group showed the lowest hepatopancreas index (HSI). Meanwhile, markedly lower feed conversion ratio (FCR) was obtained for the W group compared to the G and BK groups. Group culture results: Significantly higher SR was recorded for the BK group, and the highest limb loss rate was detected for Y group indicating the significant effects of background color on survival and aggressiveness of juvenile E. sinensis. Moreover, background color impacted the carapace coloration indices where the W, BK and Y groups showed the highest brightness (L*), redness (a*), and yellowness (b*) values, respectively. Furthermore, correlation analysis revealed a positive linear relationship between the L* value and background color (y =0.1638x+27.961, R2=0.613). In conclusion, our results demonstrated that background color significantly affects culture performance and carapace color. Black background color was shown to enhance the survival rate and reduce the limb amputation rate under group culture condition. These results provide new insights on the optimization of farming technology for juvenile E. sinensis.

Effects of sulfate on survival, osmoregulation and immune inflammation of mud crab(Scylla paramamosain) under low salt conditions

Sulfate is an important chemical component in seawater, which has a profound influence on the survival, growth, physiology and biochemistry of aquaculture species. The aim of this experiment was to study the effects of sulfate concentration on survival, osmotic regulation, oxidative stress and immune inflammation of mud crab(Scylla paramamosain). The results showed that the 72-h semi-lethal concentration of the crab was 3.373 g/L (1.353–8.589 g/L). After 28 days of cultivation, the contents of Na+-K+-2Cl− cotransporter (NKCC) and Na+-K+ ATPase (NKA) in the gill tissue of the S1 group (0 g/L Na2SO4) were significantly higher than those in the other three groups, and the sulfate content increased and the SOD activity decreased.Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were affected by sulfate content, and the content levels in the S3 group (1 g/L Na2SO4) were significantly lower than those in the other three groups. The activities of ACP and AKP first increased and then decreased with the increase of sulfate content in prepare solution, and the activities of ACP and AKP in the S3 group (1 g/L Na2SO4) were significantly higher than those in the other three groups. The absence of sulfate or high concentration of sulfate will affect the survival rate of mud crabs, and have a stressful effect on the osmotic regulation of mud crabs, inhibit oxidative stress ability, and promote inflammatory response. The purpose of this study was to explore the feasibility of sulfate-type saline-alkali water aquaculture of mud crab by studying the effect of sulfate on the mud crab under low salt conditions, and to provide theoretical basis and technical guidance for the promotion of saline-alkali water aquaculture.

Optimizing release strategies for red king crab stock enhancement: Effects of release timing

Red king crab, Paralithodes camtschaticus, was commercially important around Kodiak, Alaska, USA, in the 1960s and 1970s; however, the stock crashed in the late 1970 s and has remained closed since 1983. The lack of recovery inspired consideration of stock enhancement through the release of hatchery-reared juveniles as a means to bolster the wild population. We examined the effects of release timing on in situ survival of hatchery-reared red king crab by releasing juveniles in June, August, and September 2015 in Trident Basin, Kodiak. We monitored densities inside and outside of release plots for six months using quadrat counts to determine loss and emigration rates. Relative predation risk was determined using tethering experiments performed after each release, and predator densities were quantified using quadrat counts and predator transect counts. Initial mortality over the first 24 h was approximately 53%, and subsequent mortality rates decreased with month-of-release, likely due to a combination of larger size-at-release and seasonal changes in predation. Although predator density was consistent over time, relative predation risk of tethered crabs decreased with season, suggesting later releases may be beneficial. However, the extended hatchery rearing period needed for later releases presents other challenges, including cannibalism, and the potential for developing maladaptive traits. Stock enhancement programs must balance these trade-offs to maximize overall success. Early releases of small juveniles immediately after settlement may be optimal if large-scale hatchery communal rearing results in significant juvenile production loss and/or hatchery conditioning is impractical.

Study on survival and growth performance of freshwater crab, Barytelphusa cunicularis (Westwood 1836) using different substrates

Study on survival and growth performance of freshwater crab, Barytelphusa cunicularis (Westwood 1836) using different substrates

The effect of sulphur goatfish, sesarma, and green mussel as feed on the growth and survival of mud crab (Scylla paramamosain) in recirculation systems

The effect of sulphur goatfish, sesarma, and green mussel as feed on the growth and survival of mud crab (Scylla paramamosain) in recirculation systems

Feasibility of rice-crab (Scylla olivacea) co-cultures in the south-west coastal ghers of Bangladesh

To assess the production performance in terms of growth, survival and intactness of mud crab in co-culture with rice plants an experiment was conducted for a period of 120 days in the ghers of two villages under Paikgacha Upazilla, Khulna. The crab juvenile was collected from adjacent Shibsha River and stocked in two experimental ghers of 0.004 ha area each without considering male female ratio. The stocking density was 50 per decimal, 75 per decimal, 100 per decimal in T1, T2 and T3 treatments of two experiments, respectively. Fresh chopped tilapia fish was fed to the crab and the requirement of supplied tilapia fish was adjusted periodically in accordance with the growth performance or body weight of crab. Production and physico-chemical parameters were recorded and analyzed according to standard methods. Among these parameters salinity had significant (p<0.05) role on survival of mud crab. After 120 days of rearing we obtained average final weight of cultured crab (Scylla olivacea) was 154.6±12.19g, 135.46±21.30g and 107.23±14.87g; with the estimated yield of 995.96±193.43 kg/ha, 1179.4±266.68 kg/ha and 1144.22±544.05 kg/ha, survival was 45%, 47% and 42% in T1, T2 and T3 treatments respectively in Bayra village; On the other experimental site in Gopalpur village we obtained average final weight of cultured crab was 169.2±19.20g, 155.22±17.73g and 167.53±18.60g; with the estimated yield of 476.83±160.51 kg/ha, 793.73±361 kg/ha and 1636.19±868.32 kg/ha, survival was 25%, 27% and 22% in T1, T2 and T3 treatments respectively The yield of rice was found 6006±1021 kg/ha, 6026±991 kg/ha, 5995±1005 kg/ha in T1,T2,T3 treatments respectively in the experiment of Bayra village on the other hands in Gopalpur village the yield was 5877±1297 kg/ha, 5743±1350 kg/ ha, 5468±1190 kg/ha in T1,T2,T3 treatments respectively. Results and findings of the present study suggested that yield of rice was not hampered for rice-crab co-culture in ghers. According to the experimental results poor salinity level, temperature, water level fluctuation and winter seasons are the potential constraints in the growth, survival and intactness of rice crab co-culture in the coastal ghers of Bangladesh.

A comparison of claw removal methods on the survival and claw regeneration of stone crab (Menippe mercenaria)

Commercial and recreational stone crab (Menippe mercenaria) fisheries primarily occur along the Gulf of Mexico and Atlantic coasts of the southeastern United States and the northeastern Caribbean. The fishery is unique in that only the crabs claws are retained and the animal is returned to the water alive. While the fishery is often regarded as sustainable because it is believed to exploit the crabs natural ability to voluntarily drop (autotomize) and regenerate lost claws, the survival of de-clawed stone crabs is often low, especially when both claws are harvested. In this study, a controlled laboratory experiment was used to compare an induced-autotomy method of claw removal to the typical forced break method currently used in the fishery. For the two different claw removal methods, we compared crab survival and start time to claw regeneration as a function of one or both claws removed. Overall, we found a significant effect of the removal method and number of claws removed on crab survival, but these factors did not influence the time to start claw regeneration. Although the induced-autotomy method was several seconds slower in processing time than the typical forced break method, it resulted in a 29% increase in survival (up to 92% survival throughout the study) compared to the typical forced break method of claw removal (63% survival throughout the study). Overall, these results suggest that the induced-autotomy method of claw removal significantly increases survival of stone crabs.

Alteration of antioxidant status, glucose metabolism, and hypoxia signal pathway in Eirocheir sinensis after acute hypoxic stress and reoxygenation

Dissolved oxygen (DO) is crucial for the survival of Chinese mitten crab (Eirocheir sinensis); low DO levels adversely affect the health of these crabs. In this study, we evaluated the underlying response mechanism of E. sinensis to acute hypoxic stress by analyzing antioxidant parameters, glycolytic indicators, and hypoxia signaling factors. The crabs were exposed to hypoxia for 0, 3, 6, 12, and 24 h and reoxygenated for 1, 3, 6, 12, and 24 h. The hepatopancreas, muscle, gill, and hemolymph were sampled at different exposure times to detect the biochemical parameters and gene expression. The results showed that the activity of catalase, antioxidants, and malondialdehyde in tissues significantly increased under acute hypoxia and gradually decreased during the reoxygenation phase. Under acute hypoxic stress, glycolysis indices, including hexokinase (HK), phosphofructokinase, pyruvate kinase (PK), pyruvic acid (PA), lactate dehydrogenase (LDH), lactic acid (LA), succinate dehydrogenase (SDH), glucose, and glycogen in the hepatopancreas, hemolymph, and gills increased to varying degrees but recovered to the control levels after reoxygenation. Gene expression data showed that hypoxia signaling pathway-related genes, including hypoxia-inducible factor-1α/β (HIF1α/β), prolyl hydroxylase (PHD), factor inhibiting hypoxia-inducible factor (FIH), and glycolysis-related factors (HK and PK) were upregulated, showing that the HIF signaling pathway was activated under hypoxic conditions. In conclusion, acute hypoxic exposure activated the antioxidant defense system, glycolysis, and HIF pathway to respond to adverse conditions. These data contribute to elucidating the defense and adaptive mechanisms of crustaceans to acute hypoxic stress and reoxygenation.

Effects of prior acclimation on the survival, feed intake and salinity preference of a freshwater-adapted euryhaline crab

Abstract In estuarine systems, salinity changes by freshwater inflows and tides affect the survival and behaviour of euryhaline species. Juvenile Chinese mitten crabs, Eriocheir sinensis, are considered to live in fresh water during their complex life history, whilst some are found in coastal wetlands. To understand how juveniles disperse in estuarine residence, we investigated their survival, feed intake and salinity preference after acclimating in three different water situations (i.e., fresh water, salt water and alternation between fresh water and salt water). We supposed that behavioural alternation and salinity preference would play an essential role in their acclimation. Results showed no significant difference in survival and feed intake amongst the three groups of juveniles () in acclimation trials. However, the feed intake of crabs in each group was declining after changing water every three days. In the salinity preference experiment, crabs from fresh water preferred 0 and 12, whereas those from salinity and alternation treatments showed no preference. The salinity preference seemed to be modified by prior acclimation as well, and juvenile crabs could therefore survive and disperse in the different salinities. Our study helps to explain the complex distribution of juveniles in estuaries and provides arguments for the feasibility of Chinese mitten crabs being reared in low salinity waters.

The effects of overwintering temperature on the survival of female adult mud crab, Scylla paramamosain, under recirculating aquaculture systems as examined by histological analysis of the hepatopancreas and expression of apoptosis-related genes

The effects of the overwintering temperature (8, 12, 16, and 20 °C) on survival, antioxidant capacity, and heat shock protein (HSP) gene expression in Scylla paramamosain were examined during an experimental period of eight weeks. The effects of the temperature on survival were parabolic, with the highest and lowest survival rates occurring at 16 °C and 8 °C, respectively. Histological examination of the hepatopancreas revealed that the hepatopancreas tissue structure remained intact and that cell boundaries were clearly observed at 16 °C and 20 °C. However, hepatopancreas cells in the 12 °C and 8 °C groups appeared to be vacuolated and indistinct, respectively. Furthermore, high levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and low levels of total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) in the hepatopancreas were observed in the 8 °C group. Hsp60 and hsp70 gene expression were dramatically upregulated, but hsp10, hsp40, hsp90, and glucose regulatory protein 78 (grp78) gene expression were downregulated at 8 °C. The terminal deoxynucleotidyl transferase deoxy-UTP nick end labeling (TUNEL) method showed that there was more DNA damage at 8 °C and 12 °C than at 16 °C. Moreover, apoptosis was significantly induced with decreasing temperature, and the 8 °C group had the highest apoptosis index. Overall, these results suggest that the overwintering temperature greatly impacts the survival of mud crabs and that these effects may be mediated through antioxidant, HSP response, and apoptosis pathways. Significantly, the optimal overwintering temperature for S. paramamosain was extrapolated to be 14.2–16.1 °C. This suggests that temperature control should be considered in the process of mud crab overwintering.

Higher survival but smaller size of juvenile Dungeness crab (Metacarcinus magister) in high CO2

Dungeness crab (Metacarcinus magister) are the most valuable fishery on the U.S. West Coast and both larval and adult Dungeness crabs are important components of regional food webs. Previous experiments have shown decreased survival and a slower development rate for Dungeness crab zoea reared in water with high CO2, indicating a susceptibility to ocean acidification. In this study we reared late-stage megalopae and juvenile Dungeness crabs in both ambient and high CO2 conditions for over 300 days. Counter to expectations, crabs reared in high CO2 had a higher survival rate than those reared in ambient conditions and crabs in high CO2 transitioned more quickly in one of the stages (J5 to J6). However, crabs reared in high CO2 were generally smaller and had a higher resting metabolic rate than crabs in ambient CO2. We hypothesized that two separate mechanisms were in effect, with one process driving survival and a second process driving size and respiration rate. We further hypothesized that increased mortality in ambient CO2 could be caused by a CO2-sensitive microbial pathogen, but that size and respiration differences were caused by the direct effects of CO2 on the crabs themselves. Overall, the zoea stages seem more sensitive to CO2 than the megalopae and juvenile stages.

On the question of survival of the red king crab in trawl bycatches in the Barents Sea

The aim: Investigation of the survival rate of the red king crab during trawl fishing under the conditions of a research survey. The methods: The paper based on works which were completed in 2020–2021 through the trawl survey in the Barents Sea. King crabs were overexposed on the open deck of the research vessel and after that they were keeped in traps and dropped out in the sea water of 15 m depth and keeped there more than 1.5 hours. Crabs heath conditions were checked after the experiments. We also used data on the state of the environment in the area of work and data on the number of injured individuals in the catches. The newness: This is a first comlex research of king crabs survivability on the Barents Sea during the trawl catch. The same works were provided on the Barents Sea through traps. The results: On an open deck at an air temperature of 3 to 12 °C and overexposure of less than 3 hours, the mortality of crabs was extremely low, amounting to a maximum of 2.5 % of the number of individuals in the experiment. Over the next 3–5 hours, up to 40 % of crabs could die, and if overexposed for more than 5 hours, up to 59 %. The average proportion of dead crabs during overexposure of 3–5 hours was 5.4 ± 0.3 %, more than 5 hours — 23.4 ± 1.2 % and increased with increasing air temperature: under conditions above 10 °C 100 % survival were never seen. The average delayed mortality in the simulation of release of crabs into the sea was 11 percent. The practical significance: The results could be used for improving of fishery rules on the North fishery basign and red king crabs stock assessement. The article is not intended to calculate possible damage based on the results of control activities.

A framework for assessing harvest strategy choice when considering multiple interacting fisheries and a changing environment: The example of eastern Bering Sea crab stocks

Ecosystem Based Fisheries Management aims to broaden the set of factors included in assessments and management decision making but progress with implementation remains limited. We developed a framework that examines the consequences of temporal changes in temperature and ocean pH on yield and profit of multiple interacting stocks including eastern Bering Sea (EBS) snow, southern Tanner, and red king crab. Our analyses integrate experimental work on the effects of temperature and ocean pH on growth and survival of larval and juvenile crab and monitoring data from surveys, fishery landings, and at-sea observer programs. The impacts of future changes in temperature and ocean pH on early life history have effects that differ markedly among stocks, being most pessimistic for Bristol Bay red king crab and most optimistic for EBS snow crab. Our results highlight that harvest control rules that aim to maximize yield lead to lower profits than those that aim to maximize profit. Similarly, harvest control rules that aim to maximize profit lead to lower yields than those that aim to maximize yield, but differences are less pronounced. Maximizing profits has conservation benefits, especially when the implemented harvest control rule reduces fishing mortality if population biomass is below a threshold level.

Effects of different temperatures on the growth and survival of mud crab (Scylla paramamosain) larvae

This study aimed to evaluate the effects of temperature on the growth and survival of mud crab (Scylla paramamosain) larvae in two stages including zoea-1 to megalopa (the first experiment) and megalopa to crablet-1 (the second experiment). Each experiment was conducted in a completely randomized design with four temperature levels (27, 30, 33, and 36℃) in triplicate. Stocking density of 200 ind./L for the first experiment and 4 ind./L for the second experiment. Fiberglass tanks of 500-L (containing 300-L and 250-L of 25‰ water for the first and second experiment, respectively) were used in the experiments. The results showed that S. paramamosain larvae at zoea-3 and zoea-4 died at 33℃ or above, while the highest survival rate of this stage was found at 27℃ (11.5%). The growth and larval stage index during the zoea to megalopa stage were significantly higher in 30℃ (p<0.05) compared to those in the 27℃ treatment. In the second experiment, the survival rates of crablet-1 were highest (72.9%) at 27℃ and lowest (34,7%) at 36℃. The growth rate of crablets at this stage increased with increased temperature. The highest carapace width and weight (3.41 mm and 0.030 g, respectively) were recorded at 36℃. The findings of this study suggested that mud crab larvae should be reared at the temperature range of 27-30℃ to maximize their production.

Study of Growth and Survival of Mud Crab (Scylla serrata, Forskal) with Different Salinity Levels in culture media

The aim of this study to find out the optimal level of salinity for the growth and survival of the mud crab (Scylla serrata). The weight of crab seeds were about 47.65-51.32 grams and the carapace length ranged from 64.35-71.30 mm, then put into 12 tanks (1 m x 1 m x 0.4 m) with a density of 4 crab seed per tank. During the maintenance of this test, mangrove crab was fed with fresh chicken intestines as much as 10% of its body weight per day. Water changes are carried out more than 150% per week. At the beginning of the experiment, each tank was conditioned to the same water salinity in all experimental units, namely 33 ppt. To see the effect of differences in salinity levels on the growth and survival of mud crabs, 4 treatments were made consisting of (A) 33 ppt salt content, (B) 31 ppt salt content, (C). The salt content is 29 ppt, and (D) the salt content is 27 ppt. From the results of this experiment, it is known that a decrease in the salt content of 4 ppt is the best treatment for the growth of mud crabs, but has no effect on the survival value.

Effect of water salinity on survival and osmotic level of larval (Zoea Stage) of mud crabs Scylla tranquebarica

Mud crab of the genus Scylla are considered one of the most sought-after seafood today. This crab species has high quality and delicious aging growth rate and encourage expansion in the aquaculture sector especially in Southeast Asian Countries. However, salinity changes will cause changes in organisms osmotic pressure, and every aquatic biota has an optimal salinity range for survival. The study focuses on evaluating the effect of water salinity on the survival and osmotic levels of the purple mud crab, larvae of Scylla tranquebarica at the zoea stage. The LC50 assessment was performed in 10 different level of water salinity (0; 5; 10; 15; 20; 25; 30; 35, 40, and 50 ppt). Each treatment involved 20 ind./L of newly hatched crabs and being observed for 24 h in 10 different water salinity using 1 L volume glass container. The number of crab’s mortality were taken for each salinity regime. Larval behavior monitored during experiment. Meanwhile, the measurement of osmotic level was carried out at the salinity of 25, 30, and 35 ppt. The result shows that mud crab larvae exhibit any tolerance on the low salinity ranged from 0-10 ppt and the salinity of > 40 ppt. On the other hand, mud crab larvae were still able to survive at the salinity ranged from 20-40 ppt for more than 24 hours. The trend of the osmotic level of mud crab to survive is by hypo osmotic to iso osmotic.

Use of different seaweeds as shelter in nursing mud crab, Scylla paramamosain: Effects on water quality, survival, and growth of crab

AbstractMud crabs (Scylla spp.) are considered luxury seafood and high market value; hence, mud crab farming is well known in Southeast Asia. However, the prevalence of cannibalistic behavior in crabs thus requires shelter in the culture system to reduce conspecific cannibalism and enhance the survival of crabs. This study aims to determine the suitability of various seaweed species as shelter to improve the survival and production of mud crab Scylla paramamosain crablets. The experiment consisted of seven treatments and was randomly designed in triplicate tanks. The control treatment had no shelter (i.e., without seaweed in the culture tank), and in the other six treatments, red seaweed (Gracilaria tenuistipitata) or green seaweed (Enteromorpha intestinalis) was placed in the rearing tanks at three density levels: 0.5, 1, and 2 kg/m2. Instar 2 crablets were reared at a density of 300 ind/m2, at salinity of 15 g/L, and with continuous aeration. Crablets were fed frozen Artemia biomass to satiation for 4 weeks. Results showed that the survival of crabs in all treatments sharply declined from Week 3 to Week 4 of culture, where the 1 and 2 kg Gracilaria groups showed less reduction than the other treatments. At the end of the experiment, the average survival of crabs in the control group was lowest (17.4%), while the survival of crabs was significantly improved, varying within the ranges of 53.3–70.7% and 27.8–35.9% in the Gracilaria and Enteromorpha groups, respectively. Notably, higher survival resulted in lower growth rates in the seaweed treatments, but enhanced biomass and production of crab juveniles. Moreover, concentrations of TAN, NO2−, NO3−, and PO43− in the Gracilaria treatments were much lower than in both the control and the Enteromorpha treatments that improved water quality in the rearing tanks. The present findings prove that red seaweed G. tenuistipitata could be considered a suitable shelter for the reliable production of mud crab juveniles in the nursery phase.

Thermal Tolerance and Physiological Changes in Mud Crab, Scylla paramamosain Crablet at Different Water Temperatures

Simple SummaryThe nursery phase of mud crab (Scylla spp.)—from megalopa to several, further crablet stagesneeds to be carried out in optimal environmental conditions, until they reach a larger size suitable to being stocked to a pond. This study observed the behavioral thermoregulation of crablet instar phases, and determined the effects of several levels of water temperature on growth, survival, molting cycle, gill condition, and sex ratio in the nursery phase of S. paramamosain. In this study, optimal temperature for the long-term nursery phase of S. paramamosain, beginning with megalopa stage, was found to be 28 to 30 °C, with the possibility that water temperature could affect the sex ratio of mud crabs. Findings of this study could result in increased crablet production from hatcheries, and assist in realizing potential of monosex seed production of S. paramamosain, through temperature treatment.This study was carried out to determine the physiological changes (survival, growth, molting cycle, sex differentiation, and gill condition) of mud crab, Scylla paramamosain crablet at different water temperatures of 24, 28 and 32 °C, and ambient temperature of 27 to 30 °C. Thermoregulatory behavior, represented by preferred temperature (29.83 ± SD 2.47 °C), critical thermal minimum (17.33 ± SD 0.58 °C), critical thermal maximum (40 ± SD 0.00 °C), and thermal tolerance interval (22.67 ± SD 0.58 °C), were checked for Crablet 1 stage only (with ambient temperature as acclimation temperature).Both low (24 °C) and high (32 °C) temperatures were associated with lower growth performance, and survival rate (p < 0.05), in comparison with both 28 °C and ambient temperature treatments.Male ratio at low temperaturetreatment (24 °C) was higher (80.09 ± SD 18.86%) than for other treatments (p < 0.05), observed as 44.81 ± D 10.50%, 41.94 ± SD 19.44%, and 76.30 ± SD 5.13% for 28 °C, 32 °C and ambient temperature treatments, respectively. However, there was no significant difference observed between 24 °C, 28 °C, and ambient temperature treatments. Anatomical alterations of gill lamellae of S. paramamosain crablet for both 32 °C, and 24 °C treatments, appeared thinner and paler than at both 28 °C, and ambient temperature treatments. Based on this study, temperature of 28 to 30 °C was recommended as the optimal temperature for the long-term nursery phase of S. paramamosain.