Aquaculture 134 ( 1995) 37-47 Effects of inbreeding on growth and survival of self-fertilized catarina scallop larvae, Argopecten circular-is Ana M. Ibarra *, Pedro Cruz, Blanca A. Romero Centro de Investigaciones Biologicas de1 Noroeste S.C., Divisidn de Biologia Marina, Depto. de Cultivos Marinas, Km. I Car. San Juan de la Costa, El Comitan, A.P. 128, La Paz B.C.S. 23ooO. Mexico Accepted 28 January 1995 Abstract Artificial production of the catarina scallop in controlled conditions is a recent event. Contrary to most other mollusks artificially produced, this scallop is a functional hermaphrodite. This reproductive strategy and the mass spawning methodology commonly used for mollusks results in some self- fertilized larvae that can have an effect on the production systems due to deleterious effects of inbreeding. To determine the magnitude of these effects, three experimental groups were produced: self-fertilized, pair-mated, and mass-spawned. Larvae produced from exclusive self-fertilization and grown over a period of 18 days are smaller (112.03 pm) and have lower survival (31.27%) than larvae produced from either pair-matings (120.76 pm; 53.52%) or mass-spawning (118.31 pm; 55.76%). which were not different from each other. At the end of the rearing period, 18-day-old larvae with an inbreeding coefficient of F=0.5 showed a depression for length of 12.4% and 11.2%, and a depression for survival of 43.9% and 41.6%, in relation to mass-spawned and pair-mated groups, respectively. Lack of significant differences among the mass-spawned and pair-mated groups, as well as the cumulative distributions, indicated that self-fertilized larvae did occur among the pair-mated group probably as a consequence of the intermixed release of gametes even after the exchange of individuals between the two tanks used for each of the pair-matings. Additionally to the increase in average inbreeding coefficient due to the presence of some amount of self-fertilized larvae during mass spawning, a high variability of family size seen within the pair-mated and selfed groups is expected to contribute significantly to the total accumulated inbreeding on the medium and long run of a production system. Further loss of genetic variability is expected as a consequence of early culling of small larvae, presumably because they are self-fertilized, although we have found that self-fertilized larvae were not differentiated in mean length from pair-mated larvae until they were 11 days of age. Keywords: Argopecten circularis; inbreeding * Corresponding author. Fax ( +52-l 12)5-3625. 0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOO44-8486(95)00022-4