Utilization of Artificial Diets and Effect of Protein/Energy Relationship on Growth Performance of the Apple Snail Pomacea diffusa (Prosobranchia: Ampullariidae)
ROBERTO MENDOZA, CARLOS AGUILERA, JESUS MONTEMAYOR AND GABINO
Universidad Autonoma de Nuevo Leon, Facultad de Ciencias Biologicas, Aptdo. F-56 Cd. Universitaria. San Nicolas de los Garza, Nuevo Leon Mexico
Two feeding experiments were conducted with juvenile apple snails (Pomacea diffusa). The first was aimed at determining growth performance and adaptability with a natural vegetable source (dehydrated lettuce, D 1) compared with a composite diet of high content of fishmeal (D = 2). Snails of three different shell lengths (S1 7.5 ± 0.92, S2 = 12.6 ± 0.29, and S3 = 19.3 ± 0.46 mm) were fed at two different percentages of total weight (2% and 6%). The best results (P < 0.05) in terms of specific growth rate (SGR), shell length increase (SLI), feed conversion rate (FCR), and protein efficiency ratio (PER) were obtained with the artificial feed (D2). Snails of smaller length (SI) exhibited the best growth rate, being thus able to assimilate complex diets beginning from this length. Better results were obtained when snails were fed at 6% of their total weight. In the second experiment, a series of eight semi-purified formulations with varying levels of protein (10-40%) and energy (250-350 kcal/100g feed) were fed to triplicate groups of freshwater apple snails for 28 days. Results indicated that the SGR increased, as well as SLI, FCR, and PER with protein levels ranging from 20% to 30%. Low-energy diets (250 kcal/100g feed) were superior to high-energy diets (350kcal/100g feed) for all levels of protein tested. The SGR, FCR, and PER improved as dietary energy level was raised to 85 mg prot/kcal. Further increase of dietary energy had no beneficial effect in each protein level. Growth rates achieved in both experiments with artificial diets (13.83 and 14.16 mm/month, respectively) are far superior to those regularly obtained under laboratory conditions and even to those observed in the wild. The rapid growth rate attained and the ready acceptance of artificial diets suggest that the species could be cultured under intensive culture conditions.
The Veliger 42(2): 101-111 (April 1, 1999)