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Insight in the reproductive performance of captive male Dover sole breeders

Aim of the present study was to detect possible differences and disorders in spermatogenesis of reared (F1) male sole (S. solea L.) broodstock compared to “normal performing” captured animals, which are presently used as broodstock in a commercial farm and “normal” natural stocks. Two experiments were set up; the first to create a general view of the structure of sole testis, the second to compare cultured fish (F1), captured and wild animals on a histological and steroïdical basis. In general sole turned out to show a testis similar to higher perciform and atheriniform fishes; a lobular restricted testis. Spermatogenesis seems to take place in a normal way as described in literature though cysts already rupture when the germ cells are in the stage of spermatids. This is earlier than normally seen in fish testes.

F1 animals show significantly lower 11-ketotestosterone levels, lower gonadosomatic index, lower gonad weights, higher condition and higher absolute and relative amounts of spermatids compared to other groups.

It is suggested that a possible explanation of the low performance of F1 animals could be that low levels of 11kT give partial spermatogenesis and spermiogenesis but are not sufficient to execute spermiogenesis on large scale. A disorder in production of other autocrine or paracrine factors or hormones preceding 11kT (such as gonadotropin hormones) supporting the spermiogenesis also could indirectly be affecting the 11kT levels or other factors for the completion of spermiogenesis. Due to lack of cyclic annual temperature fluctuations and light regimes during rearing of animals it is likely that the F1 fish s internal clocks are not imprinted properly and therefore do not synchronously mature and spawn.

Reported by

RIVO
Haringkade 1
1976 CP IJmuiden
Netherlands
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