GROWTH AND SURVIVAL OF THE GIANT CLAMS, TRIDACNA-DERASA, T-MAXIMA ANDT-CROCEA, AT VILLAGE FARMS IN THE SOLOMON-ISLANDS

A series of large-scale grow-out trials for giant clams (Tridacna dera sa, T. maxima, T. crocea) were undertaken at 11 village farms in Solom on Islands. Eight hundred juveniles of each species, measuring 20-30 m m shell length (SL), were distributed equally between four replicate c ages at each site. Growth and survival of the clams were then monitore d for up to 24 months. Environmental and husbandry variables were meas ured throughout these experiments. T. derasa had the best growth and s urvival, attaining a mean SL of 150 mm +/- 19.8 s.d., and mean weight of 710 g +/- 26 s.d., after 24 months grow-out. Mean survival of T. de rasa over this period was 92.2% +/- 9.1 s.d. T. maxima grew to a mean size of 78.4 mm +/- 14.9 s.d. in 19 months, and T. crocea reached 50.2 mm +/- 8.1 s.d. in 22 months. After 19 months grow-out, survival of T . maxima was 38.9% +/- 16.6 s.d., and survival of T. crocea after 17 m onths was 39% +/- 22.6 s.d. Factors influencing growth of all species included water temperature, exposure to wave action, water clarity and water flow. Together, these factors explained between 66% and 79% of variation in growth, depending on the species. Regressions of environm ental factors against survival were a poorer fit, they explained 15% ( T. derasa), 53% (T, maxima), and 52% (T. crocea) of variability among sites. Estimated net revenue for village farmers growing giant clams f or the aquarium market was greatest for T. derasa, due to high surviva l. Although T. crocea is in great demand by the aquarium trade, it was the least suitable species for village farming because it has slow gr owth and low survival. Unless survival rates at village farms can be e nhanced considerably, T. crocea can probably be reared more successful ly in a land-based system. (C) 1998 Elsevier Science B.V. All rights r eserved.