A.P. Camacho, M. Albentosa, M.J. Fernandez-Reiriz, U. Labarta-1998
Aquaculture, 160 (1-2): 89-102
Abstract:
Reserach was carried out into the effect of phytoplankton, cornmeal and cornstarch diets on growth and biochemical composition of the seed of the little-neck clam, Ruditapes decussatus. The use of R. decussatus, fed on daily rations of Isochrysis galbana (organic weight) of 0.5 and 1% of live weight of the seed, showed an improvement in growth rate when cornstarch, which is 99% carbohydrate, was added to these diets. Thus in the case of a daily ration of 0.5%, daily growth rates increased by between 33.5 and 32.3%, depending on whether we are referring to organic weight, dry weight or live weight, when 1.5% cornstarch was added. In the case of a ration of 1% I. galbana, the addition of another 1% cornstarch lead to an improvement in daily growth rates, depending on the different weight class in question, of between 14.1 and 15.5%. When compared to a daily ration for growth consisting of 2% phytoplankton, which was considered to be the optimal ration for growth in the seed of these clams, the replacement of half the quantity of I. galbana by a quantity of cornstarch of equivalent weight gave a growth rate in terms of organic weight of 87.9% that of the phytoplankton diet, while the rates for dry weight and live weight were 89.6 and 87.9% respectively. These results improved noticeably when cornmeal, consisting of 10% protein and 90% carbohydrate, was used instead of cornstarch. In the case of a 2% phytoplankton diet, if we substituted an equivalent quantity of cornmeal for 50% of the phytoplankton, the growth rate in organic matter was the same (99.0%) as those for the diet consisting of phytoplankton alone, while growth rates in dry weight and live weight were 6.2 and 5.9% higher, respectively, than those of the phytoplankton diet. It would therefore appear that cornmeal (and to a lesser extent cornstarch) can be successfully used as a partial substitute for phytoplankton in diets for the seed of R. decussatus and its use in hatcheries and nurseries devoted to the culture of this species would lead to a considerable reduction of production costs.
(Instituto Espanol de Oceanografia, Muelle de Animas S.N., 15080 A Coruna, Spain)