Fertilization, larval
rearing and post-larval growth of the Tehuelche scallop Aequipecten
tehuelchus D'Orb., 1846
M.A. Narvarte, M.S. Pascual-2002
Aquaculture, 217(1-4) : 259-274
Abstract:
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 trochophores 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 Matías 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).
(Instituto
de Biología Marina y Pesquera "Almirante Storni", Güemes 1030. C.C.
104 (8520) San Antonio Oeste, Río Negro, Argentina, e-mail: raulg@canaldig.com.ar)