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RfdNNESTAD AND FYHN REVIEWS IN FISHERIES SCIENCE aspartic acid, glutamic acid, or taurine, dominate (Yancey et al., 1982; Pierce and Politis, 1990). The pool size varies among groups; crustaceans have particularly high cellular FAA levels. The FAA contents of marine invertebrate larvae have been documented in some species, and the available data indicate that most have high levels (see review by Fyhn E1990]). Investigations during the last decade have shown that FAA also abound in marine pelagic fish eggs (Suzuki and Suyama, 1983; Fyhn et al., 1987; Fyhn, 1989, 1990, 1993). The concentration in the egg (about 150 mrY~ is well above what is typically found in adult teleostean tissues (Fugelli, 1970; Vislie, 1980, 1982). As was the case in invertebrates, FAA in fish eggs were initially studied in order to evaluate their role as osmolytes (12iis-Vestergard, 1982; Mangor Jensen et al., 1983; Mangor- Jensen, 1986; H~lleland and Fyhn, 1986). More recently, however, FAA have been implicated as a fuel in the energy metabolism of developing marine fish eggs and larvae (Fyhn et al., 1987; Fyhn, 1989). The aggregate data from the literature, and experiments on Atlantic cod (Gadus morhua) and Atlantic halibut (Hippoglossus hippoglossus), suggested that the FAA were consumed as fuel during energy metabolism of developing larvae (Fyhn, ,1989, 1990). In general, amino acids can enter the tricarboxylic acid cycle to yield high energy nucleotide phosphates after deamination. This bioenergetic hypothesis provided a new perspective for studies regarding the FAA pool in developing marine fish eggs and larvae. In the ocean, larval fish begin exogenous feeding on various planktonic organisms that are, as mentioned earlier, rich in FAA. The developing fish larvae thereby gain access to an entirely new and additional supply of FAA. Fyhn (1990) argued that throughout 150 to 200 million years of teleost evolution in the oceans, fish larvae may have become nutritionally adapted to this exogenous supply of FAA. It also has been hypothesized that the amino acids consumed during the yolk-sac stage reflected the nutritional needs of the larvae when converting to exogenous feeding (Fyhn, 1989, 1990). That hypothesis gained much attention because it deviated from the generally accepted thinking that lipids, especially the essential highly unsaturated fatty acids (HUFA) of the n-3 and n-6 series were the key to survival and growth of fish larvae at first feeding (Watanabe et al., 1983; Henderson and Sargent, 1985). In fact, several studies have concluded that the principal factor determining the dietary value of zooplankton is their n-3 HUFA content (Kitajima et al., 1980; Watanabe et al., 1983; Walford and Lam, 1987; Izquierdo et al., 1989). In contrast, the hypothesis suggested by Fyhn (1989, 1990, 1993) focused on amino acids and the energy requirements of the developing larvae. 8. OBJECTIVES In this review, the overall objective is to present the status of research regarding the role of FAA in developing marine fish eggs and larvae. The principal focus is to elucidate the metabolic aspects of FAA during fish ontogeny and to provide a conceptual framework for catabolic and anabolic processes involving FAA. The nonmetabolic aspects resulting from the physiochemical properties of FAA are not discussed. 240