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Volume 1 (Issue #3), 1993 AMINO ACIDS IN DEVELOPING MARINE LIFE ll. RECENT FINDINGS A. FAA ABOUND IN PELAGIC EGGS OF MARINE FISH All data collected to date show that pelagic eggs of marine fish contain a large pool of FAA [Fyhn and Serigstad, 1987; Fyhn, 1989, 1990; Finn et al., 1991; Thorsen and Fyhn, 1991; R~nnestad et al., 1992a,b (Table 1)]. FAA contents vary among the fish species that have been examined. The largest pool found to date is in eggs of Atlantic halibut, H. hippoglossus (about 2300 nmol • egg-1), whereas mackerel eggs (Scomber scombrus) contain only about 30 nmol • egg'. Although a large variation in absolute amounts of FAA exists, it is largely accounted for by the variation in egg size. The FAA concentration is usually 150 to 170 mM, which generally represents about 50% of the total osmolality in newly spawned eggs. The FAA pool is established during final maturation to initiate an osmotic influx of water that swells the oocyte prior to ovulation and spawning (Thorsen and Fyhn, 1991). This takes place shortly before ovulation and results in an abrupt increase (3 to 5 times) in oocyte volume due to water uptake (Fulton, 1891, 1898; Milroy, 1898; Guraya, 1986; Mommsen and Walsh, 1988; Selman and Wallace, 1989). As a result, the previously opaque oocyte turns into a mature, transparent, and buoyant egg, ready for spawning and fertilization in a pelagic environment (Selman and Wallace, 1989; Kjesbu and Kryvi, 1989). The resulting high water content prepares the embryo for development in the hyperosmotic seawater during a period before the osmoregulatory organs become functional. During this period, the embryo depends entirely on endogenous water sources (Mangor- Jensen, 1987; Riis-Vestergard, 1987). The FAA pool represents from 20 to 50% of the total amino acid content (free plus intact protein amino acids) in pelagic fish eggs. This is higher than found for marine demersal eggs (about 2 to 3%) and the eggs of freshwater fishes (4.7% in Coregonus albula and 4.5% in C. lavaretus [Dabrowski et al., 1985ll. Thus, the FAA reservoir available to pelagic marine eggs is markedly greater than that available to either demersal marine or freshwater eggs. This observation may be related to the role of FAA in the process of oocyte hydration, a function that appears to be related to egg buoyancy and, thus, more important in marine species with pelagic eggs (Thorsen and Fyhn, 1991; Fyhn, 1993)• Pelagic eggs are common among oviparous teleosts; about 9000 of the 12,000 marine species described have pelagic eggs. Thus, it is important to include the FAA pool in future studies on physiological energetics of thy; early life history of marine fish. B. THE RELATIVE COMPOSITION OF THE FAA POOL EXHIBITS LITTLE VARIATION Although the absolute content of FAA in eggs varies (Table 1), the relative compo- sition of the FAA pool is similar in all pelagic fish eggs measured to date (Fyhn, 1990; Finn et al., 1991; Thorsen and Fyhn, 1991; R~nnestad et al., 1992a,b). Of the essential 241