Biotechnology in marine aquaculture

Abstract

Intensification of production, modernization of technique, and improvement of cultivars are needed to increase the economic efficiency of marine aquaculture industries. To help achieve such improvements, modern methods of biochemical and genetic engineering can be adapted to control biological processes which intrinsically limit the efficiency and yield of production. Such applications now have been developed for improved production of molluscs. Critical life-cycle stages of several species of abalones and other commercially valuable molluscs which thus far have proved amenable to improved control by these means include reproduction, larval settlement, metamorphosis, and acceleration of early growth. Analysis of the physiological and molecular mechanisms which control reproduction in molluscs reveals a prostaglandin-dependent regulation of spawning in abalones and certain other species. Spawning of gravid adults can be induced by the addition of prostaglandins to the surrounding seawater, or, more reliably and inexpensively, by activation of the endogenous enzymatic synthesis of prostaglandin-related spawning triggers in response to added hydrogen peroxide. Peroxide activation of the prostaglandin-dependent spawning reaction has been found widely useful for obtaining synchronous and copious release of fully competent gametes in a large number of species of abalones, oysters, scallops, mussels, clams, and other valuable molluscs; a number of these species had not been successfully spawned by other methods. Settlement and metamorphosis of many molluscan species can be brought under similar biochemical control. Most efficiently and inexpensively, the natural biochemical requirement for induction of these critical developmental processes can be met by providing competent larvae with unique amino acid constituents associated with the naturally required inducing molecules. Thus, γ-aminoburyric acid (GABA) can be used simply, safely and inexpensively to induce complete and rapid larval settlement and metamorphosis — with minimal mortality — in many commercially important abalone species. This and similar neurotransmitter-related, amino-acid-derived compounds are proving comparably effective for the reliable induction of settlement and metamorphosis in a number of other valuable molluscan species. Recent analyses of the requirements for rapid early juvenile growth in abalones reveals a mechanism of growth-control which is susceptible to exogenous hormonal acceleration. Genetic cloning and amplification of recombinant-DNA templates for the efficient production of essential growth-regulating hormones, and substances required for enhanced nutritional efficiency and resistance of cultivars, are now in progress. Genetic engineering for the direct improvement of cultivated species soon will be within reach.