Preliminary study of establishment of families and their early growth and development for manila clam (<I>Ruditapes philippinarum</I>)

Abstract

A total of 11 half-sib families and 33 full-sib families were generated by using the method of unbanlanced nest design,in Sept. 2007. Phenotypic traits of different families,such as egg sizes,fertilization rates,embryonic hatching rates,larval and juvenile growth,survival and metamorphosis were analyzed. The results showed that the differences in egg sizes and fertilization rates among the full-sib families were not significant,but those in embryonic hatching rates were significant(P0.05,n=90). The growth of each family was not the same at different stages.The fastest growth family named C2 was significantly larger than the slowest growth family named F2 by 28.24% in average shell length (P0.05,n=90)at 9 days of larval stage. D3 whose Absolute growth was the largest of all families was bigger than the average Absolute growth by 37.24%.The fastest growth family I1 at 40 days of nursing stage was significantly larger than the slowest growth family B3 by 78.29% in average shell length(P0.05,n=90). Moreover,I1 was the largest of all families in Absolute growth,and it was bigger than the average Absolute growth by 87.61%,the distributions of shell length between 400-500 μm and above 500 μm accounted for 30% and 53.33% of total shell length among I1 ,respectively. However,the growth trait depression families B1 and B3 involved in miniaturization,the distributions of shell length below 300 μm accounted for 83.33% and 90% of total shell length of B1 and B3 ,respectively. The survival of each family was different at the same stage. The highest suevival family I2 was significantly larger than the average survival by 94.14%,and the lowest growth suevival family F2 was obviously smaller than the average survival by 72.65% at 9 days of larval stage. The survivals of all families at 40 days of nursing stage were higher than 85%. The study of full-sib families at metamorphosis stage presented some phenomena,such as metamorphism time delay and metamorphism individual miniaturization. The metamorphosis time was delayed from 15 to 22 days. The average metamorphic size was (193.18±12.15) μm. The smallest metamorphic size family was K1 with(183.00±14.42) μm of shell length,and the metamorphic sizes of three families which were generated through each female mated with the same male named K were generally smaller than other families,and this was mainly due to paternal effect.The metamorphosis rates were significantly different among the full-sib families.The highest metamorphic rate family was E3 with the rate of (94.33%±0.58%),and the lowest metamorphic rate family was B2 with the rate of (7.33%±2.08%). These results suggest that I1 is a family with the best early growth and development traits,and it could be used to produce high-quality seed which presents short culture cycle,and higher production in artificial selection breeding.