Carps, Cyprinus carpio L., were exposed to a sublethal concentration of ammonia NH3 (0.102±0.059 mg.dm−3) during 3 weeks. The sensitivity of the blood picture and haemopoietic organs were evaluated. Ammonia intoxication resulted in erythroblastosis of circulating blood. Concurrently, a significant decrease in polychromatophilic erythroblasts in kidney and orthochromatic erythroblasts in spleen tissues were observed in exposed fish compared with controls. The relative proportion of erythrocytes in peripheral blood decreased and coincided with a highly significant (p < 0.01) increase of erythrocytes in spleen imprints of intoxicated carps compared with controls. Peripheral leucopenia, mainly lymphopenia as an intoxication response, was observed. In the pronephric cells significant differences in the proportion of young and adult eosinophils and the proportion of plasmocytes with vacuolized cytoplasm were found between those animals exposed to the toxic stress and the controls. Thus, the examination of haemopoietic organs has a great potential in carp health assessment.

In confined environments, the precocious reproductive efficiency of "tilapias" (various cichlid species belonging to the genera Oreochromis, Sarotherodon and Tilapia) can rapidly lead to overcrowding and nanism. Therefore, the artificial control of reproduction in these species is very important for success in their culture. Such a control may consist either in completely preventing fry production in a population, in order to improve growth, or in favouring synchronous massive productions of alevins, in order to set up cultures with homogeneous populations.

At present, some of the most intensive techniques are based on the separate rearing of male fish, either after manual sorting or following hormonal inversion treatments leading to monosex populations. New ways of obtaining a male monosex progeny are suggested, based on the viability and fertility of a new genotype YY. Recent data on the sex differentiation of tilapia gonad suggest the possible use of steroids which have been identified in vitro during the early stages of development of the testis and which exhibit high masculinizing potentialities; these studies also suggest the tentative use of specific inhibitors of the activity of some of the enzymes involved in the synthesis of the above mentioned steroids.

The occurrence of parental care is an important factor in the reproductive efficiency of tilapias. Recent data show close relationships between the chronology of the mouth-brooding behaviour in Oreochromis, and that of the ovarian cycle. A better knowledge of the underlying physiological factors may facilitate the development of new techniques for the inhibition and/or the synchronization of reproduction.

Males of Myleus ternetzi, at various maturation stages were netted in a French Guyana river. Testes were histologically and ultrastructurally analysed. Leydig cells were always present in large numbers. In mature or almost mature testes, they were characterized by a large spherical nucleus and an extensively developed smooth endoplasmic reticulum (SER) composed of very narrow tightly packed tubules. In regressed testes, most of the Leydig cells had a smaller nucleus with an irregular shape, a disorganized SER and the fine structure of the mitochondria was greatly affected. These changes would reflect different phases throughout a metabolic cycle in relation to spermatogenesis.

Pour un stock donné, les estimations de Prises Maximales à l'Équilibre (PME) obtenues avec des modèles globaux peuvent varier notablement. Dans le cas de la pêche d'albacore dans l'Atlantique Est, elles ont fortement augmenté depuis les années 1970. L'hypothèse présentée ici concerne un modèle global de dynamique de population se modifiant en fonction de l'accroissement de la surface de pêche. Cet accroissement se traduit par une diminution d'une quantité de biomasse jusqu'alors inexploitée. Selon les résultats obtenus à partir de la formulation adoptée, l'augmentation de mortalité subie par le stock serait due à l'augmentation de la surface exploitée plus qu'à celle de l'activité de pêche elle-même.

L'histologie des gonades de 187 mâles et 149 femelles de Myleus ternetzi pêchés dans des rivières guyanaises a été étudiée. Les stades et le cycle de la spermatogenèse ont été analysés à l'aide d'une méthode téréologique. L'ovogenèse a été étudiée et le stade de maturation de chaque femelle déterminé. La vitellogenèse est discontinue et au moins trois pontes pourraient avoir lieu lors de la saison de reproduction. La fécondité relative est d'environ 10 000 ovocytes par kilogramme par ponte. Bien que aptes à se reproduire toute l'année, la plupart des Myleus ternetzi se reproduiraient juste avant la grande saison des pluies.

The skeletochronological analysis of pectoral spiny rays in the silurid Arius proops, collected during the "little summer of March", confirms the presence of a slow growth period during March and April in the rivers of French Guyana. Moreover, this study shows that the longevity of the species is short, 3 and a half years for the females and 3 years for the males, while their growth rate is relatively high, especially during the first half of their life.

Age and growth of four tropical marine fish species: Lethrinus choerorynchus, Lutjanus kasmira, Nemipterus furcosus and Scomberomorus brasiliensis, were determined by means of otolith interpretation and length-frequency analysis. The results showed the presence of annual rings in the studied species. These rings were consistently interpreted and their annual periodicity tested by means of various methods. The annuli are composed of distinct daily increments, of different thickness depending of the otolith area. Growth determination by means of length-frequency analysis was problematic in some species due to the lack of clear modal classes (in the length distributions). The joint analysis of the age and the length-frequency data improved the estimation of growth parameters, and allowed the selection of results that were biologically acceptable.

The pathology of farmed tilapias is reviewed from presently available published data. The effects of intensive production systems on the aspects and importance of pathology are outlined. The main pathogenic organisms are recorded. For the moment, these pathogens seem to represent a potential threat, rather than being primary causes of losses. Conversely, environmental factors together with practical errors resulting from a lack of biological and zootechnical data on tilapias, seem to be responsible for most of the difficulties which are encountered. In the short term, intensive research in genetics, nutrition and zootechny should result in significant health improvements for tilapias.

Le rythme de dépôt des microstries sur les otolithes de Epinephelus microdon a été mesuré grâce à l'injection d'un marqueur fluorescent, la tétracycline ; 14 poissons adultes répartis en cinq lots ont été maintenus en élevage pendant plus de 1 année et leurs otolithes marqués suivant des plans d'expérience différents. En comparant le nombre de microstries comptées entre deux marques fluorescentes ou entre une marque fluorescente et le bord externe de l'otolithe au nombre de jours écoulés entre deux injections ou entre une injection et le sacrifice du poisson, il a été possible d'établir qu'une microstrie est formée en moyenne tous les 2 jours. Cette fréquence varie d'un individu à l'autre et il est montré que le rythme de dépôt des stries est corrélé positivement avec la croissance du poisson mais est indépendant de sa longueur. Parmi les hypothèses envisagées pour expliquer l'écart avec la fréquence journalière, l'arrêt du dépôt des microstries, lors d'interruptions de la croissance squelettique, a été jugée comme la seule explication satisfaisante. Cette étude met donc en évidence la nécessité de valider la période de ces stries avant toute utilisation pour estimer l'âge de poissons adultes par la technique de lecture des otolithes.

Thirty eight Satanoperca aff. leucosticta were collected in French Guyana rivers and the histology of the gonads was studied. While the structure of the ovaries follows the general pattern known for other cichlids, previtellogenic oocytes are present in the outer layer of all the testes, whatever the spermatogenetic stage. These oocytes never grow nor mature. Histological observation of all of the gonads has not revealed whether this cichlid is hermaphroditic or gonochoristic.