Genetic Improvement of Summer Flounder Broodstock

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Project Type: 
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Theme Area: 
Fisheries Resources
Sustainable Aquaculture


Thomas Kocher UNH - Department of Biological Sciences Principal Investigator

Students Involved:

Bruno Chazaro UNH - Department of Biological Sciences

Commercial hatcheries for a number of marine species are being established to support tank culture, cage culture and stock enhancement programs. Selection of genetically superior broodstock animals will greatly enhance the profitability and success of these operations.

Proposed is a pilot study to demonstrate genetic differences among sires and dams in the context of a complete factorial cross in summer flounder. The relative performance of full-sib families will be examined by communal rearing of the progenies, followed by parentage assignment using microsatellite DNA markers. We will identify differences in breeding value among parents for survival, growth rate and pigmentation. This project will establish a paradigm for the genetic domestication of a number of marine finfish species.


Develop methods for identifying genetically superior broodstock of summer flounder in a commercial hatchery.


Microsatellite markers were used to identify parentage of individual larval and juvenile fish within the hatchery, and to identify genetic effects on survival, growth and pigmentation of summer flounder raised in a common environment.


1) Decline of natural fisheries: Harvests of fish from the wild are in decline. In a trend parallel to that of many commercially important marine species, landings of Atlantic flounders decreased from 90,000 mt in 1984 to 25,000 mt in 1994. Total landings of summer flounder peaked at 30,200 mt in 1984, but since 1989 have been much lower, ranging between 6,600 and 10,700 mt.

This decline is primarily due to overfishing, as the stock is dominated by immature fish aged two years or younger. Significant increases in production from wild stocks are unlikely, since they are now being harvested beyond their maximum sustainable yield. The increasing demand for these seafood products can only be satisfied through aquaculture and stock enhancement programs.

2) Progress toward domestication: Although some fish species (e.g., carp) have been farmed for thousands of years, domestication of most marine fishes is at an early stage. For most species, the complete life cycle has not been cultured in the laboratory, requiring the collection of fingerlings or broodstock from the wild. The result is an inconsistent supply of animals that prevents the selection of animals uniquely adapted to the artificial conditions of aquaculture.

Many of the obstacles to the culture of larval flounder have been overcome. Research and commercial hatcheries have been established in the U.S. and especially Japan. There is significant interest in growing several flounder species, including summer (Paralichthys dentatus), southern (P. lethostigma), Japanese (P. olivaceous) and winter (Pseudopleuronectes americanus). The scope of these operations ranges from commercial fingerling hatcheries to tank-based or net-pen growout. There is also interest in enhancement of wild stocks and sea-ranching using cultured fingerlings.

We propose to focus our work on summer flounder for two reasons. First, it has already been established in commercial culture using both land-based and net pen systems. Second, it is a good model for other species of marine finfish being considered for aquaculture because it has the same high fecundity and delicate larval stages. Methods of genetic improvement developed for this species are likely to be useful for the genetic improvement of many other species of finfish.

3) Benefits of selective breeding: Selective breeding has played an important role in the domestication and development of agricultural species. Domestication of most fish species is at an early stage, often relying on wild-caught broodstock. As we begin to culture new fish species more intensively, it will become critical to manage the genetic composition of the animals. In those species where the life cycle has been closed in captivity, inadvertent selection for domestication has undoubtedly occurred, but has not necessarily improved traits of economic importance such as growth.

The long-term success of these aquaculture operations will depend on the development of a program for broodstock management and genetic improvement, so that the performance of these stocks can be maintained and improved over time. Selective breeding has been identified as an important research need by the Sea Grant Task Force on Flounder Culture and Stock Enhancement (Waters, 1996). We aim to develop a paradigm for genetic improvement during the early stages of domestication of marine fish species. Our aims are to quantify genetic variance for production traits and to identify genetically superior summer flounder broodstock that can be used for production of future generations in the hatchery. However, the methods we develop should be applicable to genetic improvement of any high-fecundity marine species.

A series of microsatellite markers were developed for parentage testing, and their sequences deposited in GenBank (Accession #'s AF181484-AF181489). The combination of the six markers had a very high power to determine parentage of juvenile fish on the farm.
Progeny of controlled crosses between 4 males and 4 females (16 full-sib families) were raised together in a single tank. Larvae and juveniles were sampled at various intervals and genotyped to determine parentage.
Differential representation of the families observed on day 10 may reflect variation in egg quality among females, or differences in fertilization of success of individual males. Changes in the representation of particular families were observed at later sampling dates, indicating differential survival of particular families over time.
A log-linear statistical model was used to identify maternal and paternal effects on growth rate. Significant heritability estimates were obtained for both maternal and paternal components. Progeny of the most favorable combination of parents grew twice as fast as the average, and five times faster than the least favorable combination.
Maternal effects explained variation in the incidence of albinistic malpigmentation. Only weak evidence for paternal effects were observed. It is therefore not clear whether the incidence of malpigmentation can be ascribed purely to environmental (maternal) effects, or whether genetic variation also contributes to susceptibility to this developmental anomaly.
A manuscript describing these results is in the final stages of preparation, and will be submitted during March 2004. A talented undergraduate, Bruno Chazaro, was responsible for conducting many aspects of this project.