The significance of lipids at early stages of marine

Abbreviations: HUFA, highly unsaturated fatty acids; LT, long term; ST, short term: DHA, docosahexaenoic (22:6(n - 3)); EPA, eicosapentaenoic (20:5(n - 3)); AA, arachidonic acid (20:4(n - 6)); EFA, essential fatty acids; PL, phospholipids; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; TG. triglycerides: WE, wax esters: EE. ethyl esters; FFA, free fatty acids; CO, copepods; HR, Atlantic halibut roe; DW, dry weight _ Corresponding author. Tel.: +47 73 596372: fax: +47 73 596363; e-mail: jose.rainuzzo@chem.sintef.no. 0044.8486/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SOO44-8486(97)0012l-X
Elsevier Kepwrds:c acid: Eicosapentaenoic acid
Lipids; Fatty acids; Fish larvae: Rotifers;
1. Introduction One important challenge in aquaculture is larva1 nutrition. In the last decade, most research on larval nutritional research has involved first-feeding studies. These studies have contributed to the knowledge necessary to estimate the nutrient requirements of larva1 fish. It is not easy to quantify the nutritional requirements of larval fish. However, it is believed that the optimal formulations for first-feeding larvae should simulate the yolk composition and to some extent reflect the nutrient requirements and metabolic capacities of pre-feeding fish (Heming and Buddington, 1988). The lipid content and composition of fish eggs vary between species and may change during the different developmental stages according to the physiological events and the energy demands of the eggs. Despite species differences, it is generally accepted that the quality of maternal nutrition has a direct influence on larval development throughout the period when the larvae are dependent upon endogenous energy reserves. Research on broodstock nutrition of marine fish is surprisingly scarce taking into consideration the impact of the fish brood on the quality of the egg. Knowledge of the nutritional requirement of larvae after the transition from endogenous to exogenous feeding must be provided in order to compose a satisfactory diet for the first-feeding larvae. Starvation is a major problem for larvae with small reserves of endogenous energy. The dietary lipids play an important role as sources of essential fatty acids (EFA), needed for normal growth and survival. Larvae of many marine fishes are believed to require highly unsaturated fatty acids (HUFA) of the (n - 3) series such as eicosapentaenoic acid (EPA; 20:5(n - 3)) and docosahexaenoic acid (DHA; 22:6(n - 3)) (Owen et al., 1975; Watanabe, 1982; Sargent et al., 1989). Some investigations have shown that DHA is superior to EPA as EFA for larva1 fish suggesting a different physiological function (Watanabe, 1993). The rearing of the majority of marine fish larvae requires the use of live food. The rotifer Brachionus plicatilis and the anostracan Artemia are the two organisms most extensively used for this purpose. Several studies have indicated that the critical factor for the dietary value of these organisms is their content of (n - 3) HUFA, which may be modified by various techniques (Watanabe et al., 1983, Rainuzzo et al., 1989, 1994a; Frolov et al., 199 1; Olsen et al., 1993a). Improvement of the rearing practices for the first-feeding larvae also includes the addition of microalgae together with the enriched rotifers to the rearing tanks. This has been shown to improve growth and survival during early larva1 stages (Naas et al., 1992; Reitan, 1994). The aim of this review is to outline some of the main achievements related to the significance of lipids at the early stages of marine fish.
’ SINTEF Applied Chemistry, Section @‘Aquaculture, N-70.34 Trondheim, Norway h Trondhjem Biologiccrl Station, lJnil,er.Gy of Trondheim, N-7018 Trondheim, Norway
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necessary to clarify many aspects regarding the function of these fatty acids, especially how their content at the egg stage can affect further requirements for normal growth and survival. 0 1997
Abstract The present work reviews the significance of lipids at different early stages of marine fish larvae. Lipids in broodstock nutrition are considered to be important for the quality of the larvae. Lipids affect the spawning and the egg quality of many fish species and a deficiency in (n - 3) highly unsaturated fatty acids (HUFA) in broodstock negatively affects fecundity, fertilization rate and hatching rate of the species studied. Lipids as a source of energy at the embryonic and larval stage (before first-feeding) are evaluated in relation to other sources of energy such as protein and carbohydrates. After hatching and prior to first-feeding, some marine species show a preference in catabolizing phosphatidylcholine, whereas phosphatidylethanolamine tends to be synthesized. The effect of long-term (LT) and short-term (ST) enrichment techniques on the lipid composition of rotifers has been documented using various marine oils/emulsions. The quantitative and qualitative lipid class and fatty acid composition of diets influenced the lipid and fatty acid composition of both LT- or ST-enriched rotifers. The nutritional improvement of Artemia is also important and may follow the general methods used for rotifers. The functions of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) during early stages of marine fish larvae are apparently different. High amounts of EPA in relation to DHA may create an imbalance in the structural composition of the phospholipids, which could affect the normal growth and the quality of the larvae. Turbot larvae tended to exhibit lower pigmentation success with lower DHA:EPA ratio in the total lipid fraction of the larvae, especially when the absolute amounts of EPA were high compared to those of DHA (in the total lipid and phospholipid fraction of the larvae). Considerable research is