We evaluated three alternative procedures for tagging juvenile Nile tilapia Oreochromis niloticus (1.9–13.7 g) with passive integrated transponder (PIT) tags: injection with hypodermic syringe injectors (N = 40) and abdominal surgery with or without suturing (N = 55 and 40, respectively). The survival of Nile tilapia tagged with injectors was low (10–50% at 10 d) and proportional to fish size because of the difficulty of controlling the penetration of the syringe into the intraperitoneal cavity following the piercing of the body wall. Surgically implanted fish had much higher survival rates (78–100% at 10 d). Suturing reduced the risks of tag expulsion and protrusion of the viscera through the open incision within the first 3 d following surgery (10% risk in the nonsutured fish). Over the first 3 d after tagging, tagged fish showed depressed growth rates (to a greater extent in smaller fish and proportionally greater in sutured fish) but showed normal growth later on. These results demonstrate that surgery is suitable for PIT‐tagging small juvenile Nile tilapia, which offers opportunities for studies of individual performance.
We have studied the reproductive ecology and bioacoustic signals of weakly electric mormyrid fish in Africa in order to discover the natural conditions under which acoustic signals are used and to gain insight into the evolution of their acoustic behaviour and hearing. Pollimyrus isidori migrated from a tributary of the Niger River (Mali) into a shallow (2-3 m) flood plain during the onset of the flooding seasons (August, 1991 and 1994). The
La fecondite de Baetis rhodani Pictet a ete etudiee sur tout un cycle saisonnier dans le Lissuraga, ruisseau du Sud-Ouest de la France.La variation de la fecondite suit celle de la taille; Ies femelles les plus grandes sont Ies plus fecondes et pondent les plus gros oeufs. Le maximum est atteint en hiver; le minimum estival resulte k la fois d'une diminution du nombre d'ovarioles et d'ovuies produits par ovariole.Des lignes de regression ont ete etablies entre la fecondite et plusieurs mensurations larvaires et adultes, elles ont permis de calculer chaque mois le potentiel de reproduction de la population d'apr^s des prel^vements quantitatifs de larves au dernier stade.Une relation nombre d'oeufs pondus-nombre de larves au dernier stade qui en sont issues a fourni la base d'une estimation de la production de la generation printanifere en utilisant la methode de Ia courbe d'Allen. La part prise par les jeunes stades non capturables dans la production de cette cohorte a ete calculee k partir de cette estimation.
SummaryThe fecundity of Baetis rhodani throughout a seasonal cycle is measured and the production by the spring generation is calculated from the figures obtained. Females of B. rhodani cannot be identified with certainty and therefore they were not caught wild but bred from mature nymphs in the laboratory. Various measurements were made (Fig.
Sciences of the Czech Republic, 603 655 Brno, The Czech Republic
AbstractThe lateral migration of fishes was studied during one entire flood cycle (1991) in a typical floodplain sector of the Central Delta of Niger at Batamani, Mali . The intensity and temporal course of migrations, as well as the species and size composition of migrants, were found to be correlated with the hydrological regime (river and floodplain water levels, direction and velocity of water flow in a temporary canal) . Four different types of migratory patterns were described and their typical representatives indicated . The significant role of the river as a spawning site and that of the flood plain as a nursery for most locally important fishes was also accentuated .
Summary
The eggs of Baetis rhodani were collected from natural conditions just after laying and incubated at different constant temperatures (from 7‐5°C to 27‐5°C) with a constant photoperiod. The incubation period was shorter at higher temperatures up to 25°C (8 days); above this eggs no longer hatched. The slowest development (determined by extrapolation) was at about 3°C (theoretically 130 days). The hatching period was always very short (about 3‐5 days). Fewer eggs hatched at higher temperatures.
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