1. Introduction
Increasing demand for sea urchin roe has led in the last decade to over-fishing natural Ž
. populations Conand and Sloan, 1989; Le Gall, 1990 . Several possible solutions have
Ž been tested: reseeding natural habitats with farmed juveniles Agatsuma and Momma,
. Ž
1988; Gomez et al., 1995 ; mariculture Fernandez and Caltagirone, 1994; Fernandez, .
Ž 1996 ; raising sea urchins in immerged cages, alone Fernandez, 1996; Robinson and
. Ž
Colborne, 1998 ; or with other animals polyculture with salmons notably, Kelly et al., .
1998 ; and finally land-based, closed-system echiniculture allowing control of each Ž
phase of the echinoid biological cycle Le Gall and Bucaille, 1989; Le Gall, 1990; .
Grosjean et al., 1998 . Whatever the culture method, temperate sea urchins exposed to natural conditions of
temperature and photoperiod have a seasonal sexual cycle that restrains the crop to only Ž
2 or 3 months per year Byrne, 1990; Lozano et al., 1995; Fernandez, 1996; Spirlet et .
al., 1998a . Many experimental attempts have already been made to manipulate the gonadal cycle by modifying these exogenous parameters. Most of them were successful
Ž in obtaining out-of-season gametogenesis Leahy et al., 1981; Pearse et al., 1986;
. McClintock and Watts, 1990; Walker and Lesser, 1998 . However, the experiments were
always run on specimens collected from the field, and hence, sexually in phase to begin Ž
with. Moreover, the shift in the reproductive cycle took at least 7 months Walker and .
Lesser, 1998 . Ž
. With adult sea urchins originating from cultivation see Grosjean et al., 1998 , the
first problem is to obtain individuals in phase with regard to their reproductive cycle. As gonads also act as storage organs, it is possible to induce the consumption of most of
Ž .
their content by starving the animal Lawrence, 1985; Pearse and Cameron, 1991 . This Ž
. attribute, experimentally observed, was successfully used by Spirlet et al. 1998b to
study the impact of feeding strategies on gonadal production and to obtain marketable Ž
. sea urchins all year long see Grosjean et al., 1998 . However, it has not been used yet
Ž to determine the best values of exogenous parameters mainly, temperature and photope-
. riod for optimizing the production of marketable gonads.
Several criteria have to be considered in echiniculture. The reproductive state of the gonads has to be in the correct range, from stage 3 to stage 5 according to Spirlet et al.
Ž .
1998a ; the gonads preferably need to be fleshy and firm without an abundance of gametes spilling when they are consumed; and, as previously stated, they also need to be
sexually synchronized to ensure a large quantity of exploitable individuals all at once. Ž .
This study has two objectives: 1 to determine the influence of the two major abiotic Ž
. parameters temperature and photoperiod on gonadal growth and gametogenesis of
Ž . cultured sea urchins in a closed-circuit facility; and 2 to control the reproductive cycle
and determine the best combination of temperature and photoperiod to obtain individuals ready for marketing as soon as possible.
2. Material and methods
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