| Macrobrachium rosenbergii,commonly known as Malaysian prawn and freshwater long-legged prawn,is the largest individual freshwater shrimp and one of important aquaculture shrimps in China.With the rise of shrimp culture in Southeast Asian countries and regions such as India and Malaysia,global production of M.rosenbergii is increasing day by day,becoming an indispensable delicious aquatic product in daily diet gradually.In recent years,the instability of prawn culture and production has occurred.The emergence of "iron shell shrimp" and "old shrimp" has become the primary problem that restricts the development of prawn culture industry.The main characteristics of the phenomenon are the reduction of food intake,slow growth and premature sexual maturity.At present,there is no exact identification criterion on slow growth of shrimps.Strong human subjectivity brings some difficulties to scientific research and aquaculture technology development,reducing the income of farmers,and affect the healthy and stable development of aquaculture industry.1 Meanings of studies on slow growth of M.rosenbergiiThe slow growth of shrimps and crabs in aquaculture has become a problem that can not be ignored,different reasons of this phenomenon having been put out.The prolongation of cultivation cycle increases the cost of cultivation,reducing the yield and benefits of cultivation.With the growth of aquaculture scale and the expansion of aquaculture area,the slow growth of M.rosenbergii has been studied more and more widely.But,there is still a lack of effective and reliable targeted solutions up to now.At present there are a few academic aspects of germplasm,nutrition,management and disease explaining the phenomenon of slower growth of shrimps and crabs,in which,germplasm is one of the recognized explanations in the academic field.In the process of transferring genetic material of shrimp and crab to the next generation,the absence ofsome genes or genotypes leads to fewer trait types and reduces genetic diversity by the role of artificial breeding and breeding.Regionality is a characteristic of the problem of germplasm.In the process of cultivation,aquafeed is the main source of absorbing nutrition for shrimp and crab,and the addition of essential amino acids can occasionally further improve the growth of shrimp breeding.The management methods vary from region to region,and need to be adjusted in time according to climate characteristics,weather conditions and soil types of ponds.At present,the harm of pathogens of shrimp and crab on aquaculture has been extensively studied in China.The mechanisms that viruses and pathogenic bacteria invades hosts are being revealed.In aquaculture industry,the importance of preventing pathogens is always higher than treating them when invaded.Suitable culture environment is a powerful guarantee to prevent animals from pathogens invading.According to the relevant research data and the observation of production,it is found that the slow growth of shrimp and crab is often accompanied by individual precocity,that is,the gonads are fully developed and can help completing mating before the adult size.The occurrence of precocious puberty affects the energy metabolism of shrimp and crab,which hinders the normal growth and development.Research of the level of energy metabolism during the growth and development is helpful to reveal the energy utilization and distribution mechanism of M.rosenbergii,and to provide reference for solving the symptoms of slow growth and stagnation of growth of M.rosenbergii in the course of aquaculture.2 Temperature and female-male mating ratios effect energy metabolism and growth of M.rosenbergiiBy comparing and analyzing the energy metabolism of M.rosenbergii at different temperatures and female-male ratios,the effects of temperature and male-female ratios on energy metabolism and growth of M.rosenbergii were obtained.These results are helpful to reveal the mechanism of energy utilization and distribution during the growth and development of M.rosenbergii.The results showed that the absolute energy levels for ingestion of male and female M.rosenbergii reached the maximum in temperature gradient experiment(female weight 13.57 +1.47 g,and male weight 17.97 +1.61g).The absolute energy levels for ingestion of male and female M.rosenbergii were 7687+1063J/g and 7167 +851J/g respectively at 30 ?.The absolute Energy levels for excretion of male and female increased,reaching the maximum at 30 ?(female 2383+417J/g,and male 1865 +825J/g)with rising temperature,The absolute excretory energy level was significantly different from that at the other three lower temperatures(P < 0.05).The maximum absolute energy levels for growth were 342±65J/g and477±126 J/g respectively at 26 ?,and there were significant differences in absolute growth energy comparing 20 and 22? of female and male shrimps(P < 0.05).The specific growth rates(SGR)were significantly better than the other the other three temperature levels(P < 0.05).The sum of absolute energy levels for growth and molting in high temperature groups(26,30 ?)were significantly higher than that in low temperature groups(20,22 ?)(p < 0.05).In the experiments of different female-male ratios,when female and male individuals were cultured separately,the absolute energy levels for growth of mature male shrimp decreased gradually with the increase of population of shrimps,and the level of absolute energy intake of one male shrimp was significantly higher than that of two or three(P < 0.05).The change of the absolute energy levels for growth and SGR was the relatively same as absolute energy levels for ingestion.The maximum values of energy level for growth and SGR were 304 +66J/g and 0.735% respectively with one male shrimp,and the level of absolute energy for growth of one male shrimp was significantly higher than that of two or three(P < 0.05);absolute energy levels for breath and excretion increased with the increase of population of male shrimps;the absolute respiratory energy level of three male shrimps was significantly higher than that of one or two shrimps(P < 0.05);after mating(female-male ratios 1:1,1:2 and 1:3),absolute energy levels for ingestion of sexually mature shrimps increased with the increase of population of male shrimps,no significant difference between groups(P > 0.05).The change of absolute energy levels for defecation was similar to absolute energy levels for ingestion,no significant difference between groups(P > 0.05).Absolute growth decreased gradually,with SGR decreasing,while pregnant-egg rates and absolute energy for molting increased.Therefore,combined with living habits of M.rosenbergii,the feeding levels in high temperature groups(26,30 ?)were better than that in low temperature groups(20,22 ?),and the shrimps grew better;the respiratory levels of shrimps at 1:1 were lower than that at 1:2 and 1:3,and the shrimps grew better.Mature male shrimps hinder their own process of material and energy accumulation and inhibit the growth of M.rosenbergii,by fighting,occupying and mating.This may be one of the reasons for slow growth of sexual precocious phenomenon of M.rosenbergii.3 Different female-male ratios effect growth of M.rosenbergiiWater quality is one of the important factors affecting the growth of M.rosenbergii.In this experiment,the water quality pH ranged from 7.5 to 8.5,and dissolved oxygen >4.0 g/L was suitable for the growth of M.rosenbergii.The results showed that the female-male body length ratios was 80.9%-95.6% during the test period(90 days).The female-male body weight ratios was 46.2%-84.1%.This indicated that the male body length of M.rosenbergii was generally larger than that of female shrimp in the same period.The growth rate of male shrimp's fertility at 1:1 was significantly higher than that at other levels,indicating that it was more suitable for the growth of male shrimp under this condition than 1:2 and 1:3;the growth rate of female shrimp's fertility at female-male 1:1 and 1:2 was significantly higher than that that at 1:3,indicating that the female-male1:1 and 1:2 levels were more suitable for female shrimp than that at 1:3.Based on the growth level of male and female shrimp,the female-male ratio 1:1 is more conducive to the growth and development of M.rosenbergii.It was also found that the female-male ratios affected the growth and energy accumulation of M.rosenbergii,and affected the breeding levels.The growth rates of body length and body weight of male and female M.rosenbergii at lower density level(female-male ratio 1:1)were significantly higher than that of other experimental groups(female-male ratio1:2 and 1:3)during the experimental period(P < 0.05);at the three female-male ratios,the growth rates of body length of M.rosenbergii were 2.74 cm,2.27 cm and 2.15 cm respectively,and the growth rates of body length of M.rosenbergii were 74.5 cm,59.6% and 54.5% respectively.The growth rates of body length of M.rosenbergii were 5.52 g,4.36 g and 3.99 g respectively,and the growth rates of body length of M.rosenbergii were 598.6%,414.3% and 358% respectively.In the seedling stage,the frequency of individual contact is relatively lower under sufficient space conditions.The feeding level increases with the increase of body weight,and the level of metabolism and accumulation of material and energy increases,and the growth rate accelerates.With the growth of individuals,the grabbing,occupying and mutually killing among individuals will intensify.As the male shrimp become more athletic,the fighting will become more intense.With the increase of the proportion of male shrimp in the population,the frequency of contacting,fighting or evasion among individuals,especially between males,increases,which reduces the effective feedingtime and level.At the same time,the increase of the proportion of male shrimp requires more energy to supply individual self-defense and fighting behaviors,thus reducing the energy accumulation level. |
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