Polyploid Induction And Sex Control In Several Economically Important Crustacean Species

Crustacean cultivation (especially to shrimp and crab), which has contributed largely to the employment of rural population and the augment of rural incomes, is one of the economically important industries in China, it has brought us huge social and economic benefit. Unfortunately, for the reasons of serious diseases, idioplasmic degeneration and environmental deterioration, the development of culture in shrimps and crabs encountered prodigious handicap in China in recently years. So the genetic improvement to the crustacean species is imperative. Previous researches on polyploid breeding and mono-sex culture of aquatic animal have been proved to be successful in increasing yield and improving quality. In the present thesis, the Chinese shrimp (Fenneropenaeus chinensis), the Pacific white shrimp (Litopenaeus vannamei) and the Chinese mitten crab (Eriocheir japonica sinensis) were selected as the experimental animals. Heat shock or potassium chloride (KCl) was employed to induce polyploidy in F. chinensis or E. japonica sinensis, and the feminization control was carried out in L. vannamei by heat shock.Heat shock was employed to inhibit the releasing of the first polar body to produce meiosisⅠtriploid F. chinensis. At 15℃, heat shock (temperature, 29-31℃; duration, 8-10min ) successfully induced MⅠtriploids when treated at 7min post spawning, and the highest triploid rate is about 100 percent. No aneuploid and tetraploid were observed in treated samples by inhibition of the 1st polar body. Ploidy itself did not affect shrimp larvae survival during metamorphosis, but heat shock significantly decreased the survival rate. Ploidy manipulation significantly affected the morphological characteristics of F. chinensis, the body shape of triploid shrimp is dumpy, but the diploid shrimp is slender. Based on morphological parameters, discriminating formulae for triploid and diploid shrimp at grow-out stage were developed and could be used to distinguish triploids from diploids.Triploid Chinese shrimp Fenneropenaeus chinensis were reared up by heat shock inducement to inhibit meiosisⅡ. The growth performances in full-sib diploid and triploid F. chinensis were compared to evaluate the effect of ploidy manipulation at juvenile stage under laboratory conditions. It showed that there was no significant difference (P>0.05) in tolerance observed in triploid and diploid shrimp due to abrupt salinity changes. The lethal salinity for 50% of the individuals in 96h at 23-25℃was about 2‰in both triploids and diploids. Ploidy significantly influenced (P<0.05) the survival rate, special growth rate, feed conversion efficiency and intermolt period of F. chinensis, but there were no difference of the feeding rate between the two ploidy levels. Based on the survival and growth data, the optimum salinity for the culture of diploid F. chinensis should be 20‰and for triploids it should be 30‰. At the early stage during culture, triploid F. chinensis juvenile showed no growth superiority on their diploid controls .The effects of ploidy manipulation on bioenergetics of F. chinensis were studied under laboratory conditions, and the bioenergetics'bases to explain the different growth performance during culture period were proved up. At immature stage, triploid shrimp exhibited higher oxygen consumption rate than the diploids at the range of acclimation salinities (15-35ppt) and temperatures (26-32°C), and higher ammonia-N excretion rate at some salinity level (25 and 35ppt) and temperature level (32°C). Triploid shrimp have lower energy allot for growth than that of the diploids (P<0.05). The tendencies of environmental factors on standard metabolic rate were similar between the two ploidy levels. At the early stage of gonad development, there was no difference of energy budget between triploid and diploid shrimp (P>0.05), but the triploids exhibited higher metabolic rate (P<0.05). This is the first report of bioenergetics in triploid shrimp and it likely explain the prior experimental results which with difference of growth performances between triploid and diploid shrimp.Based on morphological observation of deciduous and normal attached fertilized eggs of E. japonica sinensis, a potential morphological marker (the apparition of the plasma membrane and apparition of maximum distance between the plasma membrane and yolk mass) which can be used as the optimum starting time shocked by KCl was determined. This is the first report of morphological dynamics of early development of fertilized eggs from Chinese mitten crab, and later repeated experiments indicated that the morphological marker can be used as an indicator for highly efficient triploid induction with KCl in this crab species.To mono-sex culture, heat shock was employed to feminize the L. vannamei at different stages of embryonic development. It showed that the thermotolerance of shrimp embryos raised as the development advanced, at middle and later stages of gastrulae, heat shock (temperature, 39℃; duration, 3min) significantly increased the female ratio in the treated populations. This is the first report of feminization in L. vannamei treated with heat shock.