Two specific Enzyme Linked lmmunosorbent Assays (ELISA) for vitellogenin were developed using two different antisera anti-plasma vitellogenin purified by SDS polyacrilamide gel electrophoresis and electroelution. Purified vitellogenins migrated as single bands under SDS conditions with an apparent molecular mass of 154 and 152 kDa for Chrysichthys nigrodigitatus and Heterobranchus longifilis respectively.The ELISA was performed on 96 well microtiter plates using specific antibodies raised on rabbits and a second antibody (Goat anti-rabbit) labeled with peroxidase. Parallel displacement curves were obtained between purified vitellogenin and female plasma as well as plasma from estradiol treated fish. Both antibodies cross-reacted with the heterologous vitellogenin but the curves were not parallel, indicating different antigenic structures of the two vitellogenin molecules from the two catfish species. The reliability and the specificity of these assays allowed us to quantify vitellogenin in plasma samples during vitellogenesis of the two species. The annual vitellogenin plasma levels presented a good correlation with mean oocyte diameter and reproduction period in Chrysichthys nigrodigitatus. In Heterobranchus longifilis the mean oocyte diameter is almost constant all year round, but vitellogenin levels presented significant variations with higherlevels corresponding mainly to the low gonado-somatic index values observed during the dry seasons.

L'examen macroscopique, histologique et cytologique des ovaires de Barbus holotaenia adultes récoltés dans le bassin de la Luki entre juillet 1986 et septembre 1988 a permis de décrire six stades de développement des ovaires et sept stades au niveau des ovocytes et des follicules. Quelques conclusions biologiques et écologiques sont tirées de ces différentes observations. La fécondité individuelle partielle est comprise entre 0,005 et 0,018 ovocytes par kg de la masse du poisson.

Chrysichthys nigrodigitatus and Heterobranchus longifilis are two commercially important African catfish species that have been studied for their reproduction and breeding possibilities in the lagoon waters of Ivory Coast. C. nigrodigitatus is characterized by an annual reproductive cycle with a vitellogenesis period from March to June. The reproductive season coincides with the short rainy season which is characterized by lower water temperature and salinity at the beginning (September) and by a progressive rise of these parameters at the end of the season (November). The previtellogenic oocytes enter vitellogenesis at an average diameter of 320 μm. This initial oocyte stock is reconstituted progressively as soon as the spawning is achieved and lasts for a period of approximately 3 months. Fully vitellogenic oocytes reach an average diameter of 2.4–2.8 mm by the end of June. The maturation is possible only if a male and a female are confined in artificial spawning receptacles. Maturation and spawning generally occur within the following 3 to 5 weeks for 30 to 80% of the females. When the non-spawning females are kept in the nests they maintain fully vitellogenic oocytes for 3 months with a continuous atresia of the larger oocytes, while the ovaries of the non- spawning females, placed out of the receptacles, exhibit a complete atresia of all the vitellogenic oocytes. After an HCG-induced ovulation, a new reproductive cycle of H. longifilis can be achieved in less than a month. The previtellogenic oocytes enter vitellogenesis at an oocyte diameter of about 380 μm and become fully vitellogenic after 15 days (1.2–1.6 mm in diameter). If maturation is not artificially stimulated the females remain at the same stage of vitellogenesis while larger oocytes undergo atresia and are continuously replaced by growing vitellogenic oocytes.

This work examines the effects of constant long and short days on the hormonal profile of plasma17β-oestradiol (E2) levels and the ovarian vitellogenic events, as well as on the fecundity, time of spawning and egg quality of sea bass. Constant short days first administered in April advanced spawning (by 45 days on average) whereas exposure to constant long days from the same date induced a delay (averaging 38 days) compared to controls reared on an ambient light regime (Lat. 40°N). These light regimes produced shifts in the profiles of plasma 17β-oestradiol and in the percentage of the vitellogenic oocytes according to the spawning time of the respective groups. Relative fecundity of the short day group was similar to controls (257,000 versus 230,000 eggs/kg spawned female, respectively). However, in the long day group, relative fecundity was reduced to one half that of control fish (124,000). Plasma oestradiol showed a bimodal pattern under long days and vitellogenetic and atretic oocytes were present for a longer period (6-7 months compared to 4-5 months in controls). In summary, in this paper we describe, for the first time in the sea bass, the effect of constant photoperiod regimes on the 17β-oestradiol plasma profiles, the timing of spawning and the quality of the eggs.

Changes in the morphology of the ovary are described during maturation and it is established that it is a homogeneous structure for sampling purposes at maturity stages four and five. Several aspects of vitellogenic oocyte growth and recruitement were examined as criteria to ascertain whether the annual fecundity can be determined in Solea solea just prior to spawning. The first criterion was whether a hiatus develops in the size frequency distribution between the previtellogenic and vitellogenic oocytes just prior to spawning. We were unable to demonstrate this feature in sole from division VIId (N = 5) or IVc (N = 5) but it was present in two out of five fish from division VIIe and all fish examined from division VIIa (N = 5) and IVb west (N = 5). The hiates occurred between 175 and 250 µm (cohort size 25 m) in the size frequency distribution and measured between 25 and 75 µm. Oocyte size frequency distribution from mid spawning and late spawning-spent sole from division IVc showed a hiatus in 9 out of 10 fish which became wider as the residual annual potential fecundity declined. Next the rate of recruitment and growth of vitellogenic oocytes was studied in sole sampled at monthly intervals (July 1993 to February 1994) from division VIId in relation to the start and duration of the annual spawning season. The growth rate of the leading oocyte cohort was 2.73 × 10−5 mm3 per day on 20 September and increased to 3.91 × 10−3 at a mean diameter of 839 µm by 10 February just prior to spawning. However, the observed maximum growth rate, even when adjusted for the positive influence of temperature, allowed little scope for previtellogenic oocytes to complete maturation during a spawning period of 60 days. The recruitment of viltellogenic oocytes was 3013 oocytes per day on 3 August and declined rapidly as spawning approached. In the three months prior to spawning no significant increase was found in the annual potential fecundity. An analysis of a sample of spawning fish from IVc demonstrated that 88% had less than 50% of their predicted potential fecundity remaining in the ovary. The mean batch fecundity was 8 400 (SE ± 13 363) and in conjunction with existing data on spawning frequency and duration gave a realised fecundity close to the potential fecundity. It is concluded that for all practical purposes the sole can be regarded as having a determinate fecundity in all the areas studied.

The regulation of potential fecundity by follicular atresia was assessed in pre-spawning and spawning sole. In ICES areas IV and VII the prevalence of atretic oocytes in pre-spawning fish varied between 0.04 and 0.69 and the relative intensity varied between 0.017 and 0.076. During spawning in division IVc the prevalence of atresia varied between 0.45 and 0.57 and the relative intensity between 0.022 and 0.058. If we assume a turnover rate of 9 days the loss from the potential annual fecundity, during spawning, in division IVc would be 12.4%.