Fertilization, larval rearing and post-larval growth of the Tehuelche scallop Aequipecten tehuelchus D'Orb., 1846

Experiments on fertilization (self-fertilization and cross-mating), embryonic density, larval feeding, survival and larval settlement on natural substrata were carried out in order to identify some of the basic requirements of the early life history of Aequipecten tehuelchus reared under hatchery conditions.

In self-fertilization, the main developmental stages were represented by the initial stages, mainly nonfertilized oocytes and embryos going through early divisions. In cross-matings, there was a displacement towards the stages characteristic of the culmination of the incubation phase, namely trocophores and D-larvae. The number of larvae finally obtained from self-fertilized crossings was lower than that reached in cross-matings (P<0.05).

The relation 10 sperms: 1 oocyte, commonly used in hatchery manipulation, yielded low fertilization rates (10%). Fertilization success obtained from adding 30 and 50 spermatozoids/oocyte was significantly higher (36.01% and 32.64%, respectively).

Cross-fertilized eggs were incubated at three different densities (354, 708 and 1062 oocytes mm−2). Nonsignificant differences were observed in the number of D-larvae produced (SNK: P>0.05).

One-week-old larvae of A. tehuelchus were cultured to the pediveliger stage in order to assess larval performance under three different dietary regimes. Growth and survival were assessed on larvae fed on: (1) Isochrysis galbana (T-Iso)+Chaetoceros calcitrans, (2) Pavlova lutheri+C. calcitrans, and (3) T-Iso+P. lutheri+C. calcitrans. Maximum growth rates were detected in larvae fed diets that included P. lutheri.

Larval mortality rate varied along the culture period, being maximum during the first week of culture (0.24–0.43), and furtherly decreasing towards the end of the planktonic life (0.15 and 0.29).

Pediveliger settlement was performed at the hatchery using the preferential substrata used by this species in the natural grounds: scallop shells (San Matı́as Gulf), and Ulva lactuca thalli (San José Gulf). Larvae massively settled both on shells (0.613 individuals cm−2) and thalli (0.624 individuals cm−2). Spat density on experimental collectors was directly related to the surface offered (P<0.05; r=0.74), but not to the substrate type (P>0.05). Scallop growth rate was similar on both substrates in the experimental period (59 days) even when growth decreased on U. lactuca at the end probably due to habitat deterioration on algal thalli (increase of organic matter and associated microfauna).