盐度对长牡蛎和近江牡蛎及其杂交稚贝生长和存活的影响

2011年8月以长牡蛎自繁组GG(Crassostrea gigas♀×C.gigas♂),近江牡蛎自繁组AA(C.ariakensis♀×C.ariakensis♂)、正交组GA(Crassostrea gigas♀×C.ariakensis♂)、反交组AG(C.ariakensis♀×C.gigas♂)为实验材料,开展了稚贝对盐度的适应性研究。结果发现长牡蛎的最适生存盐度为15—35,最适生长盐度为25—35;近江牡蛎的最适生存盐度为10—25,最适生长盐度为20—25;GA的最适生存盐度为15—30,最适生长盐度为15—30,AG的最适生存盐度为20—30,最适生长盐度为20—25。GG对低盐度敏感,AA对高盐度敏感,AG具有高盐度存活的杂种优势,在盐度30时,中亲杂种优势HG×A为13.32,单亲杂种优势HGA和HAG分别为1.89和27.88,在盐度40时,HAG上升到400,GA和AG都不具有生长优势。杂种稚贝对盐度适应介于双亲之间,且表现出一定程度的父系遗传特点。

Effect of salinity on growth and survival of Crassostrea gigas, C. ariakensis and juvenile hybrids

The overall aim of distant hybridization is to obtain hybrids between varieties, species, or genera via the transfer the genome of one species to another, which results in changes in phenotypes and genotypes of the progenies. Hybridization is essentially the fusion of genotypically different sex cells and the development of a new organism that combines the hereditary character of both parents. Heterosis is often characteristic of the first generation of hybrids, as displayed by an increased capacity for adaptation and improved viability. Hybridization between different species, categories or advanced genetic relationships between species can yield various characteristics (species, category), penetrate species or category boundaries, expand genetic variation, and create new mutation types or even new species. Hybridization is also a source of hereditary variation, which is one of the main factors in evolution. Distant hybridization mimics the evolution of a species, so it is an important experimental tool in the study of evolution. Samples of Crassostrea gigas and C. ariakensis were purchased in Dalian and Shenzhen in August 2010. They were identified as being of pure stock by molecular genetic analysis. The samples of C. gigas and C. ariakensis were spawned in the laboratory and crosses obtained in the same year. The effect of salinity on two hybrid progenies (GA and AG) and two inbred groups (GG and AA) was investigated during August 2011 using an experimental design incorporating seven salinities (10, 15, 20, 25, 30, 35 and 40 ppt). The experiments were carried out in 60-L white barrel-shaped tanks and performed in three replicates. To achieve the required salinity levels, the salinity was controlled and monitored every hour. In order to maintain adequate dissolved oxygen levels, the barrels were aerated slowly and any dead juvenile mollusks were removed immediately to prevent deterioration of water quality. The results showed that the optimum salinities for survival and optimal growth for the various experimental crosses were as follows: 15-35 and 10-25 ppt, respectively, for GG; 10-25 and 20-25, respectively, for AA; 15-30 and 15-30 respectively, for GA; 20-30 and 20-25, respectively, for AG. The GG inbred group was sensitive to low salinity, as were the AA inbred progeny. Heterosis was positive for the AG hybrid progeny at the higher salinity, but negative for both the GA and AG hybrids for growth as measured by shell height. The heterosis of H_G×A was 13.32 at a salinity of 30 ppt, while the single parent heterosis of H_GA and H_AG was 1.89 and 27.88, respectively. The single parent heterosis of H_AG increased to 400 at a salinity of 40 ppt. The adaptability of juvenile hybrid was shared between parents but showed a certain degree of paternal inheritance. This study examined the effects of various salinities on the growth and survival of Crassostrea gigas, C. ariakensis and juvenile hybrids. Through hybridization, trait-specific germplasm can be identified and traits can be improved, but not necessarily growth performance. This study has the potential to be the basis for increased aquaculture production of oysters, and to advance our knowledge of interspecies cross breeding, reproductive isolating mechanisms and heterosis utilization.