Assessment of ovarian development and its relation to mating in wild and pond-reared Litopenaeus vannamei shrimp in a commercial hatchery
E.
Palacios, I.S. Racotta, M. Villalejo-2003
Journal
of the World Aquaculture Society, 34(4): 466-477 (from ISI Current Contents)
Abstract:
The present study compares three scales for evaluation of ovary development
stage in wild and pond-reared shrimp. An external visual scale was assessed
according to color and size of ovaries observed through the exoskeleton in
live shrimp by staff of a commercial hatchery. Shrimp were then sacrificed
to obtain gonadosomatic index, and gonads were scaled according to their
color and size upon dissection. Finally, a portion of ovaries was processed
for histological analysis, from which oocyte diameters were obtained, and
females were evaluated with another scale based on cytological organization
of gonads and on frequency of oocyte sizes. The certainties of the external
and internal scales were analyzed, based on differences in gonadosomatic
index and oocyte diameter and by comparison with the more accurate scaling
obtained by histological analysis. The external scale was, in general, less
accurate than the internal scale. Maturation stage in pond-reared shrimp was
underestimated or overestimated more frequently than in wild shrimp. The
implications for hatchery operation and possible reasons are discussed.
Pond-reared shrimp were found to have a non-linear relation between gonad
weight and body weight, but this relation was linear for the larger wild
shrimp. This reduced the validity of gonadosomatic index in pond-reared
shrimp, which were still growing. Thus, oocyte diameter, which was not
affected by body weight in growing shrimp, represents a more accurate
numeric measure of ovary development. Spermatophores were found attached to
the thelycum in females only at the cortical stage of maturation,
independent of origin. However, a significant proportion of fully mature,
pond-reared shrimp did not have an attached spermatophore, possibly
indicating lower mating success or poorer spermatophore adherence in these
shrimp.
(Ctr. Invest. Biol. Noroeste, AP 128, La Paz BCS
23090, Mexico)