Christine Spirlet

Optimization of gonad growth by manipulation of temperature and photoperiod in cultivated sea urchins, Paracentrotus lividus (Lamarck) (Echinodermata)

A starvation and then feeding method was developed to produce about 100% marketable sea urchins, Paracentrotus lividus, in 3 1/2 months. This method is needed because the reproduction cycle is desynchronized in the conditions imposed during the somatic growth stage in land-based closed systems. The major advantages of starving the animals are resetting the reproductive cycle to the spent stage (gonads almost devoid of sexual cells) and stressing the individuals so that they mobilize and restore the nutritive phagocytes, filling them with nutrients. Batches of sea urchins starved 2 months beforehand were fed ad libitum for 45 days with enriched food under eight combinations of four temperatures (12°C, 16°C, 20°C and 24°C) and two photoperiods (9 and 17 h daylight). In our system, the best combination was 24°C and 9 h daylight for growth as well as for gonad quality. The gonadal indices obtained (in dry weight) were over 9% at 16°C and over 12% at 24°C, which are better than what is found in the field for this population.

Reproductive cycle of the echinoid Paracentrotus lividus: analysis by means of the maturity index

Summary The gonad and maturity index cycles of the echinoid Paracentrotus lividus and their relations with environmental abiotic parameters are assessed after 2 years of observation in southern Brittany, France. The gonadal cycle is briefly described and eight gonadal stages are characterized. The annual cycle, the time of spawning and the period of gonadal growth are well established, suggesting they are controlled externally. The reproductive cycle has three main phases: the growing phase (late autumn and winter) when gonads accumulate reserve material; the maturation phase (spring and early summer) in which gametogenesis then spawning take place; and the spent/regenerating phase when relict gametes are resorbed by the nutritive phagocytes, the gonads being virtually devoid of sexual cells. The maturity index based on the histological diagnosis of gonads and the use of circular data and polar graphical representation make it possible to reliably determine the spawning period, the rate of gametogenesis a...

Experimental study of growth in the echinoid Paracentrotus lividus (Lamarck, 1816) (Echinodermata)

Abstract Multimodal size frequency distribution (i.e., a few individuals growing very fast and a few individuals growing very slowly) among an originally homogeneous cohort of juveniles Paracentrotus lividus is observed in reared conditions when they are 6–24 months old. The splitting of this cohort into homogeneous size-classed subgroups results in an increased growth of the smaller animals that catch up with the bigger ones in 4 months time. This indicates that the smaller animals are not genetically less productive and suggests they were inhibited in their growth due to the presence of larger ones. Supposing such growth inhibition also occurs in the natural environment, the observed mechanism could be very efficient in stabilizing field populations of aggregative echinoid species by maintaining a protected pool of small individuals with high growth potential but inhibited by the density of larger ones.

Optimizing food distribution in closed-circuit cultivation of edible sea urchins (Paracentrotus lividus: Echinoidea)

In the framework of echinoid cultivation, whose objective is to succeed in continuously producing large amounts of edible sea urchins (Paracentrotus lividus) under controlled conditions (aquaculture), gonadal growth is to be optimized. Among the various parameters influencing the production of roe, the quantity of food distributed was tested for optimization. After a 1-month fast, echinoids were fed artificial food pellets (enriched in soybean and fish proteins) for different periods of time over 48 h, the food thus being available ad libitum for 8, 16, 24, 32, 40, and 48 h; the cycles were repeated for a month. The results show that the quantity of food intake and the gonad index peak after about 35 h of food availability. This suggests food should be distributed discontinuously for optimal gonad production and minimal waste.