Effect of broodstock nutrition on reproductive performance of fish

M.S. Izquierdoa,*; H. Fernández-Palaciosa; A.G.J. Taconb    a GIA, Grupo de Investigación en Acuicultura, P.O. Box 56, 35200 Telde, Las Palmas, Canary Islands, Spain
b The Oceanic Institute, Makapuu Point, Waimanalo, HI 96795, USA
* Corresponding author.

Abstract

In many cultured fish species, particularly in those new for aquaculture, unpredictable and variable reproductive performance is an important limiting factor for the successful mass production of juveniles. An improvement in broodstock nutrition and feeding has been shown to greatly improve not only egg and sperm quality but also seed production. Gonadal development and fecundity are affected by certain essential dietary nutrients, especially in continuous spawners with short vitellogenic periods. Thus, during the last two decades, more attention has been paid to the level of different nutrients in broodstock diets. However, studies on broodstock nutrition are limited and relatively expensive to conduct.

Lipid and fatty acid composition of broodstock diet have been identified as major dietary factors that determine successful reproduction and survival of offspring. Some fish species readily incorporate dietary unsaturated fatty acids into eggs, even during the course of the spawning season. Highly unsaturated fatty acids (HUFA) with 20 or more carbon atoms affect, directly or through their metabolites, fish maturation and steroidogenesis. In some species, HUFA in broodstock diets increases fecundity, fertilization and egg quality. As in higher vertebrates, vitamin E deficiency affects reproductive performance, causing immature gonads and lower hatching rate and survival of offspring. For example, elevation of dietary a-tocopherol levels has been found to reduce the percentage of abnormal eggs and increase fecundity in the gilthead seabream (Sparus aurata). Ascorbic acid has also been shown to play an important role in salmonid reproduction, where the dietary requirement of broodstock was higher than that of juveniles. Among different feed ingredients, cuttlefish, squid and krill meals are recognized as valuable components of broodstock diets. The protein component of cuttlefish and squid together with their optimal concentration of HUFA appear to be responsible for their positive effect on reproductive performance. Both polar and nonpolar lipid fractions of raw krill were found to effectively improve egg quality. © 2001 Published by Elsevier Science B.V.

Keywords

Broodstock

Nutrition

Spawn

Egg quality

Fatty acids

Vitamin E

Received 1 October 2000; accepted 31 December 2000

1 Introduction

Broodstock nutrition is without doubt one of the most poorly understood and researched areas of finfish nutrition. To a large extent, this has been due to the necessity of suitable indoor or outdoor culture facilities for maintaining large groups of adult fish and the consequent higher cost of running and conducting extended broodstock feeding trials. However, as in human and livestock nutrition (Leboulanger, 1977), it is clear that the dietary nutrient requirements of broodstock will be different from those of rapidly growing juvenile animals. Moreover, as in other animals, it is also clear that many of the deficiencies and problems encountered during the early rearing phases of newly hatched finfish larvae are directly related to the feeding regime (including nutrient level and duration) of the broodstock. The aim of this paper is to review the major studies conducted to date on the effects of broodstock nutrition on reproductive performance of farmed fish.

2 Effect of food restriction

Food restriction itself can seriously affect spawning success. A reduction in feeding rate has been reported to cause an inhibition of gonadal maturation in several fish species, including goldfish (Carassius auratus, Sasayama and Takahashi, 1972), European seabass (Dicentrachus labrax, Cerdá et al., 1994a) and male Atlantic salmon (Salmo salar, Berglund, 1995). In seabass, after 6 months of feeding broodstock with a half food ration, growth rates decreased and spawning time was delayed and eggs as well as newly hatched larvae were smaller than those obtained from fish fed full rations (Cerdá et al., 1994a). In female seabass, the detrimental effects of food restriction were associated with reduced plasma estradiol levels (Cerdá et al., 1994a). However, the expression of the GtH genes was not affected by food restriction in mature female goldfish (Sohn et al., 1998).

3 Effects of nutrition on fecundity of broodstock fish

Several methods have been developed to assess the egg quality of fish (Kjorsvik et al., 1990; Fernández-Palacios et al., 1995). One of the parameters, fecundity, has been used to determine egg quality, which is also affected by a nutritional deficiency in broodstock diets. Fecundity is the total number of eggs produced by each fish expressed either in terms of eggs/spawn or eggs/body weight. Reduced fecundity, reported in several marine fish species, could be caused either by the influence of a nutrient imbalance on the brain-pituitary-gonad endocrine system or by the restriction in the availability of a biochemical component for egg formation.

The elevation of dietary lipid levels from 12% to 18% in broodstock diets for rabbitfish (Siganus guttatus) resulted in an increase in fecundity and hatching (Duray et al., 1994), although this effect could also be related to a gradual increase in the dietary essential fatty acid content. Indeed, one of the major nutritional factors that has been found to significantly affect reproductive performance in fish is the dietary essential fatty acid content (Watanabe et al., 1984a,b). Fecundity in gilthead seabream (Sparus aurata) was found to significantly increase with an increase in dietary n - 3 HUFA (polyunsaturated fatty acids with 20 or more carbon atoms, essential for marine fish) levels up to 1.6% (Fernández-Palacios et al., 1995), and similar results have been reported in other sparids (Watanabe et al., 1984a,b,c, 1985a, b). However, studies on the reproductive performance of Nile tilapia (Oreochromis niloticus), as indicated by the number of females that spawn, spawning frequency, number of fry per spawning and total fry production over a 24-week period, show that the performance was much higher in fish fed a basal diet supplemented with soybean oil (high in n - 6 fatty acids, essential for this fish species; Watanabe, 1982) and relatively low in fish fed a 5% cod liver oil supplemented diet (high in n - 3 fatty acids) (Santiago and Reyes, 1993). Fish fed the diet containing cod liver oil showed the highest weight gain (Santiago and Reyes, 1993).

With the exception of salmonids and turbot (Scophthalmus maximus), muscle lipid reserves are utilised during the maturation of the ovaries (Lie et al., 1993). In sparids, the fatty acid composition of the female gonad is greatly affected by the dietary fatty acid content, which in turn significantly influences egg quality in a short period of time (Harel et al., 1992). Thus, in gilthead seabream, the fatty acid composition of eggs is directly affected by the n - 3 HUFA content of the broodstock diet. Both the n - 3 fatty acid and n - 3 HUFA content of gilthead seabream eggs increased with an increase in n - 3 HUFA dietary levels, mainly due to the increase of 18:3n - 3, 18:4n - 3 and 20:5n - 3 (EPA, eicosapentaenoic acid) contents in the eggs (Fernández-Palacios et al., 1995). A positive correlation was observed between the levels of n - 3 HUFA in the diet and the eggs with the EPA concentration being more readily affected by dietary n - 3 HUFA than DHA (docosahexaenoic acid). Rainbow trout (Oncorhynchus mykiss) fed an n - 3 deficient diet during the last 3 months of vitellogenesis produced a moderate effect on the incorporation of DHA into egg lipid whereas EPA concentration decreased by 50% (Frémont et al., 1984). However, the levels of other fatty acids in the eggs were not affected by the fatty acid composition of the diet. Selective retention of DHA has also been found during embryogenesis (Izquierdo, 1996) and during starvation (Tandler et al., 1989) denoting the importance of this fatty acid for the developing embryo and larvae. Polyunsaturated fatty acids can also regulate eicosanoid production, particularly prostaglandins, which are involved in several reproductive processes (Moore, 1995), including the production of steroid hormones and gonadal development such as ovulation. Fish ovaries have a high capacity to generate eicosanoids, among them prostaglandin E (PGE) derived from cycloxygenase action and leukotrienes LTB4 and LTB5 derived from lipoxygenase action (Knight et al., 1995). Inhibitors of the latter enzyme reduced the gonadotropin-induced maturation of European seabass oocytes (Asturiano,...