1. Introduction
The aquaculture industry depends on the availability of high quality juveniles which will grow rapidly to commercial size. Many factors, including those affecting gametoge-
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nesis and broodstock conditioning Sastry, 1979; Lannan, 1980 , modify the perfor- mance of larval and both early and later juvenile stages. Survival of larvae is partly
dependent on stored energy reserves derived from the eggs. Performance of the larval rearing system, reflected in the proportion of ova which survive to the early-juvenile
stage, may be substantially improved by managing broodstock conditioning to maximize
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the proportion of viable gametes Lannan et al., 1980 . Seasonal studies of molluscs in connection with their reproductive stages have clearly
shown that environmental factors, mainly temperature and food availability, are closely Ž
related to reproductive performance Lannan et al., 1980; Robinson, 1992a; Ruiz et al., .
1992a . Differences in bivalve gamete quality have primarily been ascribed to differ- Ž
. ences in environmental conditions Helm et al., 1973; Bayne, 1976 . When adult Ostrea
edulis individuals were supplemented with extra food, many of the broods were liberated sooner, and the corresponding larvae grew at an enhanced rate and provided
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greater spat yields than broods from the control stock Helm et al., 1973 . Conditioning of Crassostrea gigas kumamoto in the laboratory at 24
8C resulted in production of Ž
. gametes 2–4 weeks earlier than at 20
8C Robinson, 1992a . Oysters conditioned at 208C and fed supplemented lipid mixtures or algae, released higher number of eggs compared
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to those from non-fed broodstock individuals Robinson, 1992b . O. edulis pre-condi- tioned in fertilised seawater produced more broods of larvae than oysters pre-condi-
tioned in unfertilised seawater and conditioning of these broodstock with a mixture of microalgae was more productive than conditioning with a single species of microalgae
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. Millican and Helm, 1994 .
Glycogen is an important energy source for some bivalves during gametogenesis ŽTaylor and Venn, 1979; Robinson et al., 1981; Barber and Blake, 1985; Martınez,
´
. 1991 . High levels of lytic oocytes toward the end of gonadal maturation of pectinids
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have been ascribed to a lack of glycogen Le Pennec et al., 1998 . Lipids have also been reported to play a major role in gamete development. The viability of larvae was
Ž significantly correlated with their proportion of lipid at the time of liberation Helm et
. al., 1973 . In Pecten maximus, the total lipid and triglyceride content in the gonad
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faithfully reflect the course of sexual maturation Besnard, 1988 . Some fatty acids have been shown to be of paramount importance for gonad maturation and the quality of the
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broods Soudant et al., 1996a . The scallop Argopecten purpuratus has become a commercially important species in
Chile and its culture has developed extensively during the last decade. This scallop is a functional hermaphrodite and exhibits continuous gametogenic activity with two main
Ž spawning peaks: one in late summer and another in autumn Wolff, 1988; Le Pennec et
. al., 1998 . It thus needs a rather high temperature and food abundance for optimal
reproductive performance. The present study was designed to evaluate the interactive effects of three diets and
two temperatures on the reproductive conditioning of the scallop A. purpuratus with the aim of obtaining gametes yielding larvae with high survival.
2. Material and methods
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