James E. Lannan

The Controversy about Salmon Hatcheries

Abstract The use of hatcheries has been a subject of lengthy debate in the management of salmon and trout resources in the Pacific Northwest. The problem has resulted in part from the wide distribution of hatchery fish in circumstances where natural populations were disadvantaged by management policy involving hatchery fish and the confusion of the effects of management with the effects of artificial propagation. Recently, the controversy has been epitomized by the recommendations to fisheries management agencies that excess hatchery fish should not be allowed to spawn in the wild, and hatchery fish should be excluded from salmon populations listed under the Endangered Species Act. The authors of the present article disagree with those recommendations and conclude that hatchery fish have an important role in recovery and supplementation of wild stocks. The present article is an attempt to help give balance to the discussion by providing a different perspective on hatchery fish and the literature pertainin...

Broodstock management of Crassostrea gigas: I. Genetic and environmental variation in survival in the larval rearing system

Abstract Larval survival of Crassostrea gigas in a hatchery rearing system was evaluated by diallel analysis. Variance in survival was observed to be comprised of genetic and non-genetic components, inferring that the rearing environment and the management of broodstocks both influence rearing success. The genotypic variance was observed to be non-additive; the specific mating combinations influenced larval survival substantially. This influence results from stringent genetic regulation of the rate of gametogenesis. For a given rearing environment, maximum larval survival occurs in matings between individuals expressing the optimum stage of gonadal development.

Broodstock management of Crassostrea gigas: Environmental influences on broodstock conditioning

Abstract Maximum larval survival is realized when broodstock are in an optimum stage of gonadal development and the efficiency of larval culture may be substantially improved by using only optimally conditioned broodstock. The conditioning requirement to bring broodstock into this optimum stage is dependent upon the stage of gonadal development at the commencement of conditioning and upon the rate of conditioning. The stage of gonadal development at the commencement of conditioning may be determined directly or inferred by understanding the annual cycle of gonadal development occurring in the broodstock. The rate of conditioning, on the other hand, is regulated by the conditioning environment. In the present study, we have observed the influence of three components of the conditioning environment: temperature, salinity, and supplemental feeding on the rate of gonadal development during hatchery conditioning of broodstock. The rate of gonadal development is a function of temperature intensity and time rather than accumulated thermal exposure. Salinity exerted a negative influence on the rate of development in oysters conditioned at salinity levels below 30 parts per thousand (ppt). Furthermore, when oysters conditioned at 20 ppt relative to 30 ppt were spawned and the larvae were reared under standardized hatchery conditions, larval survival was markedly reduced in the former. Fecundity of broodstock was 60% greater when fed an algal food supplement of the diatom Thalassiosira pseudonana relative to starved controls, although the rate of gonadal development and gamete viability was not significantly different. Using these empirically determined functions, a simplistic quatitative model may be employed to predict broodstock conditioning requirements in order to increase the proportion of optimally conditioned brood oysters.

Broodstock management of Crassostrea gigas: II. Broodstock conditioning to maximize larval survival

Abstract The results of time-course conditioning trials indicate that there is an optimum conditioning interval during which the proportion of viable gametes is at a maximum. When matings are accomplished before or after this optimum interval, reduced gamete viability results. In this case, spawning and fertilization may appear to be normal, but setting success is substantially reduced. The degree of conditioning required to reach this optimum window is dependent on the stage of gonadal development in the broodstock when conditioning is started, and reflects substantial seasonal variation, which is repeated on an annual cyclic basis. Performance of the larval rearing system, reflected in the proportion of ova which survive to the spat stage, may be substantially improved by managing broodstock conditioning to maximize the proportion of viable gametes. This may be accomplished by empirical observation of the annual gonadal cycle in the area where the broodstock is maintained, and then determining the optimum conditioning interval for the various seasons.

Broodstock management of Crassostria gigas: IV. Inbreeding and larval survival

Abstract Average larval survival in crosses of seven F-1 lines mated in all possible combinations have been evaluated by analysis of variance. Based upon this analysis, the null hypothesis that the population means of incrosses and outcrosses do not differ significantly is accepted. It is concluded that any inbreeding depression of larval survival which may occur through two generations of inbreeding is negligible.

Broodstock management of Crassostrea gigas. III. Selective breeding for improved larval survival.

Abstract General combining abilities were calculated for seven inbred lines of Pacific oysters. Separate analyses were accomplished for males and females. High general combining abilities for males were observed in two lines and for females in one line. An inverse relationship exists between general combining ability for males and females of a given line. The use of lines selected for high general combining ability of gonadal development would result in substantial improvement of hatchery broodstocks with respect to larval survival.

Application of a conceptual fitness model for managing Pacific salmon fisheries

Abstract A conceptual fitness model for managing Pacific salmon fisheries to maintain the long-term reproductive fitness of breeding populations is described. The genetic objective is to maintain the variance of fitness at a level which allows the stock to perpetuate itself in the face of fishing and natural mortality. Functional relationships of the model are reviewed. The expressions relate the variance of fitness to the number of spawners, age structure, and immigration. Adjustment of the model to accommodate the different life histories of Pacific salmon is demonstrated by application of the functional relationships to fictitious chum ( Oncorhynchus keta ) and pink ( O. gorbuscha ) salmon stocks. The demonstration includes estimating changes in the variance of fitness resulting from pre-selected escapement levels, and the escapement required to maintain the variance of fitness constant.

Vibriosis Vaccination of Chum Salmon by Hyperosmotic Infiltration

Abstract When fry of chum salmon (Oncorhynchus keta) started to feed, they were vaccinated with Vibrio anguillarum bacterin by hyperosmotic infiltration. Mortalities of vaccinated and unvaccinated fish were compared in ambient and controlled challenge experiments. In the controlled challenge experiment, cumulative mortalities after 10 days were 6% in the vaccinated group and 63% in the unvaccinated group; in the ambient challenge experiment the respective cumulative mortalities after 70 days were 6% and 96%. The differences were statistically significant (P < 0.005), indicating that survival was highly contingent on vaccination under the conditions observed.

Application of a genetic fitness model to extensive aquaculture

Abstract Substantial progress has been made in the breeding improvement of a variety of species of fish and shellfish. At the present time the opportunities for genetic improvement of aquaculture broodstock are limited to intensive production systems where the environment remains relatively constant and predictable from one generation to another. This is not the case in extensive aquaculture systems where the environment may be highly variable from one generation to the next. Stocks of fish and shellfish produced in extensive aquaculture systems may experience reduced genetic diversity as a consequence of inbreeding and genetic drift if only a small proportion of the population is used as broodstock. This report describes the application of a genetic fitness model developed for natural resource management to the problem of broodstock management in extensive aquaculture. The model describes the probability distribution of stock fitness in terms of population numbers, age structure, and immigration into the broodstock. The output of the model is the size and structure of the broodstock required to maintain the probability distribution of fitness in subsequent generations.