Introduction Material and methods

1. Introduction

Knowledge of the biochemistry and metabolism of the processes that occur during maturation are essential for a complete understanding of crustacean reproduction Ž . Mourente et al., 1994 . Lipid deposition during maturation is crucial to reproduction and early larval development because lipids are known to play several essential roles in Ž the metabolism of crustaceans Teshima 1972, 1997; Pillay and Nair, 1973; Middleditch . et al., 1980; Teshima and Kanazawa, 1983; Galois, 1984; Harrison, 1990 . Apart from being a major source of metabolic energy and the main form of energy storage, lipids also supply essential fatty acids needed for the maintenance and integrity of cellular Ž membranes, and serve as precursors of steroid and moulting hormones Teshima, 1972; . Harrison, 1990 . For the freshwater prawn Macrobrachium rosenbergii, however, most studies that have investigated lipid metabolism and requirements have been restricted to larval and Ž juvenile stages Sandifer and Joseph, 1976; Chanmugam et al., 1983; Hilton et al., 1984; Briggs et al., 1988; Reigh and Stickney, 1989; Devresse et al., 1990; Sheen and D’Abramo, 1991; Teshima et al., 1992, 1997; D’Abramo and Sheen, 1993; Querijero et . al., 1997; Roustaian et al., 1999 . As a result, little is known about the specific function of the different lipid classes and their components in the maturation of this prawn. The purpose of the present work is to describe the distribution and variation of total Ž . lipids, lipid classes and fatty acids in the midgut gland MG , ovary, and muscle tissue of wild-caught M. rosenbergii females at different stages of ovarian development. These data may lead to a better understanding of the relative importance of the different components of the lipid fraction in the reproduction of this economically important species.

2. Material and methods

Adult M. rosenbergii females were captured in the Mae Klong River, Amphur Muang, Province of Samut Songkhram, Thailand, from July to September 1998. Soon after capture, female prawns were divided into five groups according to their stage of ovarian development. Stages were identified according to the size, colour and general Ž . aspect of the ovary as presented by Chang and Shih 1995 : v Stage I: no ovarian tissue can be observed. This absence is characteristic of both non-developed and spent females; v Stage II: an ovary with a small spot of yellow colour found near the posterior part of the carapace; v Stage III: the ovarian tissue, with an orange colour, can be observed from the posterior part of the carapace to the area just in front of the epigastric tooth; v Stage IV: the ovarian tissues have grown and extended to the area of the epigastric tooth; v Stage V: the ovarian tissues have extended to the anterior part of the carapace. Ž . Ž After blotting the prawns dry, wet weight to the nearest 0.1 g and total length from . the tip of the rostrum to the end of the telson were recorded. Females were then sacrificed and the ovary and MG were removed by dissection and weighed to the nearest Ž . 0.01 g. Samples of muscle tissue were also collected. The gonado-somatic GSI and Ž . midgut gland somatic indices MSI were calculated as the percentage of the weight of the gonad or MG to total body weight, respectively. When tissues of one individual were insufficient for analysis, tissues were pooled from two to four individuals. All samples were maintained at y20 8C until analysis. 2.1. Lipid analysis Ž . The total lipid, lipid class composition and fatty acid methyl esters FAME of the ovary, MG, and muscle tissue were determined using standard analytical procedures. Ž . Total lipids were determined according to Folch et al. 1957 , following the modifica- Ž . tions of Ways and Hanahan 1964 . FAME composition was verified by gas chromatog- Ž . raphy according to Coutteau and Sorgeloos 1995 . Lipid classes were analysed using Ž . high-performance thin-layer chromatography HPTLC as proposed by Olsen and Hen- Ž . derson 1989 . 2.2. Data analysis Differences between the stages of ovarian development were analysed by one-way Ž . analysis of variance ANOVA and, when pertinent, by Tukey’s honest significant Ž . difference HSD test. The homogeneity of the variances of means was checked by the univariate tests of Cochran, Hartley and Barlett. A minimum of three replicates for each Ž . tissue was analysed. Results are presented as means standard deviation SD .