| A series of laboratory experiments were conducted to determine the effects ofsalinity on the growth, molt, energy budget, respiratory metabolism, osmoregulationand heat shock protein of Portunus trituberculatus. The primary results were listed asbelow.1Effects of salinity on the growth, molt and energy utilization of juvenileswimming crab Portunus TrituberculatusThis experiment was conducted in the laboratory to investigate the effects ofsalinity on the growth, molt and energy utilization of juvenile PortunusTrituberculatus. In the experiment, the crabs were held at five salinity (15,20,25,30,35) and cultured in rectangular aquariums. Each salinity treatment was quadruplicated,with each replicate consisting of3stage7juveniles. During the50-day experiment,mortalities and incidence of “molt death syndrome” were recorded daily, while theintermolt period, carapace length, carapace width and wet weight were measured ateach molt.Results of the experiment showed that salinity could significantly affect thegrowth and energy utilization of P.trituberculatus. At the salinity of20,25and30,food intake (FId) of P.Trituberculatus was lower, while food conversion efficiency(FCEd) was higher. At salinity of30, FCEd was significantly higher than that of15and35, but no difference to20and25treatments. The assimilation efficiency (K1)and net growth efficiency (K2) of20,25and30treatments were significantly higherthan that of others. After the experiment, P.Trituberculatus at25and30obtained higher wet body weight, relative body weight gain and SGR, and there was asignificant difference when compared to15and35treatments but no difference to20and25treatments. Regression analysis showed that P. Trituberculatus at26.3had thehighest SGRd. Growing from Ⅶ instar to Ⅹ instar, P. Trituberculatus got a moltrecycle (MC) ranging from18.9to23.5days, and there was no significant differenceamong these treatments. Nevertheless, the MC of30treatment was3.1~4.6daysshorter than the others. In this study, MDS occurred at salinity of15, which indicatedthe lower salinity could play a role in inhabiting the molt of P. Trituberculatus, whilethe new shell hardening was inhabited by higher salinity. The results preliminaryshowed that the swimming crabs would have a better performance of growth as wellas the synchronous molt, when the salinity of culture water is controlled at around25.2Effects of salinity on the respiratory metabolism of swimming crab PortunustrituberculatusJuveniles and adults of swimming crab, Portunus trituberculatus, culturedbetween15and35constant salinities in the laboratory, were used to evaluate theimpact of salinity on the respiratory metabolism. Oxygen consumption, nitrogenexcretion and enzyme activity, including hexokinase (HK), pyruvate kinase (PK),succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH), were chosen as itsindicators. Physiological responses of P.trituberculatus to salinity levels and bodyweight were obtained in this paper, by analyzing above parameters. Resultsdemonstrated that the interaction of salinity and size didn’t exhibit a significant effecton the respiratory metabolism. In this study, the effect of salinity on the oxygenconsumption rate other than nitrogen excretion rate was not significant (P>0.05),which was different to that of size, while both oxygen consumption rate and nitrogenexcretion rate showed significant changes with the ontogeny of swimmingcrab(P<0.05). For O:N ratio, the influence of salinity was not significant (P>0.05),which was contrary to the factor of size. It was noticed that the activity of HK and PKchanged significantly with the ontogeny other than salinity (P<0.05). Excluding LDH,no significant correlation between enzymes of respiratory metabolism and salinitywas observed (P>0.05). However, the crab enzymes except SDH and LDH of gillschanged significantly pre and post maturity (P<0.05). The preliminary experiment showed the effect of body size on the respiratory metabolism of P.trituberculatus wasbigger than that of salinity, while it is suggested by information of this paper, thatlong-term salinity acclimatization may lower or even eliminate the difference ofrespiratory metabolism of P.trituberculatus.3Effects of salinity fluctuation amplitudes on the osmoregulation and Hsp ofswimming crab Portunus trituberculatusTo determine the effect of salinity fluctuation on the Portunus trituberculatus,osmolality, two osmotic enzymes(Na+/K+-ATPase and carbonic anhydrase) in the gills,and heat shock proteins (Hsp70and Hsp90) in muscles and gills were measuredduring experiment of salinity fluctuation which lasted72h. In this experiment, foursalinity fluctuation amplitudes were designed and they were30-25(S5),30-20(S10),30-15(S15),30-10(S20)，with crabs before salinity change used as control.The results showed salinity fluctuation significantly affected the osmolality,osmotic enzymes and Hsps.(1) When medium osmolality was higher than800mOsm/Kg, the hyaemlymph osmolality showed a positive correlation with salinity;while it keeped stable relatively in a certain range when medium osmolality was lowerthan800mOsm/Kg.(1) Osmolality of P.trituberculatus decreased with salinitydecrease, and changed more dramatically with increasing salinity fluctuationamplitudes.(2) Activities of Na+/K+-ATPase and carbonic anhydrase (CA) didn’tshow a significant increase until12h after salinity changes. When experiment finished,their activities were higher than that of pre-experiment and increased with increasingsalinity fluctuation amplitudes.(3) The violent changes of Hsp70and Hsp90occurredduring the first12h, and they mainly reached highest values at3to6h. After theexperiment, the Hsp showed an increase with decreasing salinity. Apparently, the timewhen Hsps reached the peak was prior to that of osmotic enzymes beginning to risegreatly, and this seemed to indicate a possible role of Hsp in activation of osmoticenzymes during the adaption of P.tritubercuatus to the dilute seawater. Based on theexperiment, it can be concluded that a salinity fluctuation amplitude of over10pptwas harmful to the osmoregulation and growth of P.trituberculatus. |
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