Yellow perch strain evaluation I: Genetic variance of six broodstock populations

As a prelude to strain selection for domestication and future marker assisted selection, genetic variation revealed by microsatellite DNA was evaluated in yellow perch, Perca flavescens, from four wild North American populations collected in 2003-2004 (Maine, New York, North Carolina, and Pennsylvania,), and two captive populations (Michigan and Ohio). For the loci examined, levels of heterozygosity ranged from H-e=0.04 to 0.88, genetic differentiation was highly significant among all population pairs, and effective migration ranged from low (N(e)m=0.3) to high (N(e)m=4.5). Deviation from Hardy-Weinberg equilibrium was regularly observed indicating significant departures from random mating. Instantaneous measures of inbreeding within these populations ranged from near zero to moderate (median F=0.16) and overall inbreeding levels averaged F-IS=0.18. Estimates of genetic diversity, Phi(ST), and genetic distance were highest between Michigan and all other broodstock groups and lowest between New York and Ohio. Genetic differentiation among groups did not correlate with geographic distance. Overall, the patterns of variation exhibited by the captive (Michigan and Ohio) populations were similar to patterns exhibited by the other wild populations, indicating that spawning and management practices to date have not significantly reduced levels of genetic variation. (C) 2007 Elsevier B.V. All rights reserved.

A new three-phase culture method for Manila clam, Ruditapes philippinarum, farming in northern China

Studies on reproduction, hatchery management, and culture of Manila clams Ruditapes philippinarum were carried out in an attempt to optimize their culture conditions and techniques. Results from these studies led to the development of a three-phase culture method for Manila clam farming in northern China. The key components of the new method were: 1) early spawning and over-wintering indoors (greenhouse); 2) optimized larval culture conditions and techniques; 3) juvenile rearing in shallow, fertilized nursery ponds; 4) optimized stocking size and density and substrate for mudflat grow out. Broodstock were maturated indoors for a month from early April to early May. Primarily because of higher water temperatures in the greenhouse the clams spawned more than one month earlier than in the natural environment. From May to July, juveniles were reared for 1-2 months indoors to a size of 2.0-3.0 mm in shell length before being moved to outdoor, pre-disinfected, nursery ponds. Juveniles were then reared in the nursery ponds for one month to about 1.0 cm before being transferred to the mudflat for grow out. Juvenile clams in nursery ponds grew considerably faster than in the natural environment probably because of higher temperatures and more abundant natural food. During grow out, the clams were reared for 4-7 months until they reached a market size (3.0-3.3 cm). Juveniles produced after August were over-wintered in the greenhouse in which the water temperature was about 3 degrees C higher than that of the outdoor environment. Juveniles grew at an average rate of > 20 mu m day(-1), while in the natural environment no growth was observed during winter because of low temperatures. Juveniles in the greenhouse grew to 2-3 mm by the following March before being moved into outdoor nursery ponds. The three-phase culture method not only shortened the production period from spawn to market size from 24-36 months to about 10-14 months, but also prolonged the spawning season from 2 to 7 months, resulting in increased production of seed and market-size clams. Compared with the traditional method, the new method could increase the yield of market-size clams by 10-11 times, and increase the profit per ha mudflat by as much as 124 times and the profit per kg market-size clams produced by 13 times. (c) 2006 Elsevier B.V. All rights reserved.