Hybrid Breeding Studies On Two Wild Introduced Populations Of Macrobrachium Rosenbergii

In recent years, scorpion shrimp phenomenon continued to occur in China’s major farming areas of Macrobrachium rosenbergii. Aquatic scholars generally believed that scorpion shrimp phenomenon was the result of long-term inbreeding of Macrobrachium rosenbergii which led to the decline of reproductive traits. The scorpion shrimps changed the population structure of original Macrobrachium rosenbergii, main reasons were as follows:First, the orange clamp male shrimps (OC) with growth potential were replaced by precocious scorpion shrimps (small males, SM);Second, the blue clamp male shrimps (BC) which were the final individual form were replaced by precocious scorpion shrimps (small males, SM);Third, the scorpion shrimps mated with sexually mature females in advance in ponds which led to parts of females couldn’t molt growth on time. The three main reasons led to the significant decline of specifications in males and females which ultimately affected the whole specifications in ponds, made each pond harvest yield greatly reduce, and caused the breeding benefit decline significantly. This study intended to select the two wild populations introduced from Bangladesh (Macrobrachium rosenbergii dacqueti) and Vietnam (Macrobrachium rosenbergii rosenbergii)as the parents, designed corresponding hybrid combinations, studied and analysed the various morphological characteristics, growth traits and reproductive parameters of the parents and offspring. To explore the heterosis of F1hybrids in order to be able to produce hybrids with good growth traits in future, and to improve the degradation problem of the artificial breeding populations of germplasm of Macrobrachium rosenbergii in our county. In this study, the parents were selected through the hybrid offspring in order to prepare for the future establishment of corresponding family, which could breed hybrids with excellent traits, and applied to actual production practice, in order to create greater economic benefits.Results were as follows:1. In the positive hybridization group of five females weighted22～32g, the mean brood volume was25740seeds/tail, the fertilization rate was60.0～69.7%(mean64.58%), the mean body weight relative fecundity was976.2seeds/g, the mean length relative fecundity was2370.34seeds/cm, the mean gonad coefficient was9.586%;In the reverse hybridization group of five females weighted25.6～35.1g, the mean brood volume was30242seeds/tail, the fertilization rate was60.9～67.3%(mean67.3%), the mean body weight relative fecundity was941.92seeds/g, the mean length relative fecundity was2674.44seeds/cm, the mean gonad coefficient was8.838%;The reproductive parameters mean in each positive, reverse cross combinations was not significant in this study (P)0.05), the fertilized eggs were relatively larger, and the fertilized eggs size of the hybrid combinations was reached to941.9～976.2seeds/g. The greater eggs could develop into greater larvae which could help to enhance the viability of the population.2. The first test bred128,000positive cross seedings and106,000reverse cross seedings, and the seedings survival rate was65%;The second test bred186,000positive cross seedings and122,000reverse cross seedings, the seedings survival rate was68%, and the seedings specification was reached to more than0.8cm. Under the same cultivation conditions, the positive and reverse cross of F1tolerated more than its parents for ammonia, and they had a certain tolerance of heterosis for ammonia.3. There was a linear relationship between the body length and weight in the positive and reverse cross of F1, and the body weigh would be a corresponding increase as the growth of body length; There was a linear relationship between the body length and weight in the populations introduced from Bangladeshand and Vietnam, and the body weigh would be a corresponding increase as the growth of body length; There were a few differences between the positive cross of F1and the female parents in mean body length, the body length of positive cross of F1was generally0.3833cm longer than the female parents; There were a few differences between the positive cross of F1and the female parents in mean body weight, the body weight of positive cross of F1was generally1.6667g heavier than the female parents; The mean body length and weight may be the same in the positive cross of F1and the male parents; There were a few differences in the positive and reverse cross of F1in mean body length, the body length of positive cross of F1wasgenerally0.2833cm longer than the reverse cross of F1;There were a few differences in the positive and reverse cross of F1in mean body weight, the body weight of positive cross of F1was generally1.333g heavier than the reverse cross of F1;There were a few differences between the reverse cross of F1and the female parents in mean body length, the body length of reverse cross of F1was generally0.2667cm longer than the female parents; There were a few differences between the reverse cross of F1and the female parents in mean body weight, the body weight of reverse cross of F1was generally1.1g heavier than the female parents; The mean body length and weight may be the same in the reverse cross of F1and the male parents. The mean body length and mean body weight in the positive and reverse cross of F1was better than its female parents in this study; The mean body length and mean body weight of the positive cross of F1was better than the reverse cross of F1. The results showed that the positive cross of F1had a certain heterosis.4. The overall average of blue clamp male shrimps (BC) in different male populations were as follows:The populations introduced from Bangladesh was51.55%, the populations introduced from Vietnam was23.92%,the pond breeding populations of positive cross of F1was69.30%, the pond breeding populations of reverse cross of F1was34.46%. The overall average of blue clamp male shrimps (BC) reflected the proportion of large size male shrimps in the breeding population structure, the higher the ratio, the more the large-sized males in the breeding population structure, and the greater the whole shrimps breeding population size.The overall average of blue clamp male shrimps (BC) of the pond breeding populations of positive cross of F1was higher than their parents in this study, which reflected a certain heterosis.