Jean Claude Philippart

Is captive breeding an effective solution for the preservation of endemic species

Abstract Captive breeding and the release of captive-bred individuals into the wild are among the techniques used for the conservation of rare and endangered fish species. After a brief description of the methods of captive breeding and the establishment of breeding stocks, this paper provides examples of the application of these techniques to endemic fish species of arid regions in south-western USA and examines some current cases and the future possibilities for their use in the Mediterranean region. Special attention is given to the analysis of the strict constraints imposed on fish breeding for conservation purposes, in which the aim is to produce fish with all the morphological, behavioural and genetic characteristics of the taxa to be conserved, and which are capable of effectively adapting to the natural environment when introduced. In terms of genetic management of captive populations, the fundamental problems which are faced involve the categorization of the species-resources to be conserved (identification of cases of inter- and intra-specific introgression), the establishment of founder stocks that contain the maximum genetic diversity depending on the genetic structure of the species (strong intra- or interpopulation variability), and the retention of genetic variability during captive breeding (the need to reduce to the minimum the phenomena of genetic drift, inbreeding and unintentional selection of non-adapted genotypes). Because of these difficulties and risks in terms of genetic conservation, captive breeding should remain a temporary safeguard measure, while awaiting the implementation of measures for protecting species in their restored original habitat or translocation to strictly protected substitute habitats. With this aim in view and in conclusion, the paper suggests methods for organizing a critical plan to safeguard the most endangered species or subspecies in the Mediterranean region by captive breeding.

Hybridization success of three common European cyprinid species, Rutilus rutilus, Blicca bjoerkna and Abramis brama and larval resistance to stress tests

Hybridization success at early developmental stages and larval resistance to osmotic, thermal and fasting tests in roach Rutilus rutilus, silver bream Blicca bjoerkna, common bream Abramis brama and their F1 hybrids were investigated. Results revealed that hybrid survival rates were similar to parents. At the eyed embryo stage, however, a maternal effect was observed as a general trend during hatchling and larval stages. After these stages, hybrids displayed a higher survival rate than their parents. Under stress tests, no survival was observed after 40 min for osmotic and thermal shocks and after 24 days for the prolonged fasting test in these species and their F1 hybrids. The median survivals of hybrids were intermediate between the two parents. For total mortality, hybrids were also affected by a maternal effect but to the advantage of the hybrids.

Mating patterns of first-generation hybrids of the roach, Rutilus rutilus (L.), and the silver bream, Blicca bjoerkna (L.)

Mating patterns among first-generation hybrids of the roach, Rutilus rutilus, and the silver bream, Blicca bjoerkna, between hybrids or with parent-species males, have been investigated under experimental reproduction conditions. The results reveal that the level of sexual activity of these hybrids is high. Hybrid females mated simultaneously and successively with all types of male, resulting in fertilised eggs. Individual participation of roach males in mating was never observed, however.

Relationships between circulating androgens, aggressive behaviour and breeding tubercles in males of the common bream Abramis brama L. in an aquarium environment

In this study, relationships between circulating androgens, aggressive behaviour and breeding tubercles in males of common bream Abramis brama were examined in an aquarium environment. The breeding tubercles of fish were counted, the number of attacks was quantified by male status and circulating rates of testosterone and 11-ketotestosterone from blood plasma were analysed using radioimmunoassay procedures. The results revealed that no significant differences were found between circulating testosterone and 11-ketotestosterone in territorial and nonterritorial males. Furthermore, no significant correlations were found between circulating androgens, androgens and aggression, androgens and tubercles and breeding tubercles and aggression in common bream by male status. However, territorial fish displayed a significantly higher level of aggressive behaviour and breeding tubercles than nonterritorial fish. In natural environments, the occurrence of breeding tubercles during the spawning season could contribute to identifying the behavioural status of common bream males.

Spawning behaviour and mating success in hybrids of silver bream (Blicca bjoerkna L.) and rudd (Scardinius erythrophthalmus L.) in an experimental environment

The egg-release, mating, courting and aggressive acts for the spawning behaviour as well as the survival rates after spawning at stages of eyed embryos, viable hatchlings, and larvae to dry food consumption for the mating success were studied in cultured silver bream Blicca bjoerkna × rudd Scardinius erythrophthalmus hybrids at their first sexual maturity. Experiments were conducted in experimental environments simulating natural reproductive conditions of the parental species. Spawning behaviour was analysed over 1 day from 8.00 to 18.00 hours using a remote-controlled video. Mating success was assessed from eggs and hatched embryos collected on the spawning ground. The results showed that these hybrids exhibited all the reproductive behaviours of the parental species with significantly more courtship than mating. Each egg-release act was accompanied by mating behaviour, involving all the experimental males. A surprising aggressive behaviour was observed in one male which attacked all other experimental fish. Successful mating resulted in the presence of fertilized eggs, the production of hatched embryos in experiments, and the survival of larvae at the dry food consumption stage. However, the low viable hatchling rate observed could indicate a very low chance of survival for these hybrids in rivers in which the occurrence of post-F1 individuals may be more possible by backcrossing.

Artisanal gill-net fishery catches of the catfish, Schilbe intermedius (Teleostei: Schilbeidae), in two tributaries of the Ouémé River, Bénin, West Africa

Artisanal fishery gill-net catches of the catfish Schilbe intermedius were studied in the Okpara and Zou tributaries of the Ouémé River, Benin in 1999 and 2000. The largest fish caught at the Toué and Kpassa stations measured 26.2cm and 24.5cm (TL) respectively. The success of artisanal fishing for schilbeids varied during the day, with the highest fish catches being recorded at approximately 22h00 and at 07h00 and the lowest between 13h15 and 16h15. The monthly production at Kpassa varied between 9.0g and 900.0g (average 206.3g) and between 3.3g and 17 320g (average 2 603.4g) at Toué. The monthly production fluctuated considerably. At the two stations, fewer fish were caught each month in the second year than in the same months in the first year. Nets of between 10 and 15mm stretch mesh were the most efficient. Above 15mm, gill-net fishing became less effective. Large fish were often taken with gill-nets of 20–30mm stretch mesh. Beyond these mesh sizes, the gill-net yield and catch decreased.

Effects of three agricultural by-products on cage culture growth performances of a landlocked population of Sarotherodon melanotheron (Teleostei: Cichlidae) in man-made Lake Ayame, Côte d\'Ivoire

In man-made Lake Ayame, a 180-day cage culture feeding trial was conducted to investigate the effects of three agricultural by-products — chicken droppings, wheat bran and corn bran — on the survival rates, mean daily weight gain and feed conversion ratio in juveniles of a landlocked population of Sarotherodon melanotheron. Results were compared to those obtained from fishes fed on a local commercial diet and a group of unfed fishes. Survival rate (SR), mean daily weight gain (MDWG) and feed conversion ratio (FCR) were better for fish fed on the commercial diet (SR: 95.0 ± 4.2%, MDWG: 0.26 ± 0.00 g.d−1 and FCR: 4.27 ± 0.47) than for the unfed fish (SR: 53.0 ± 0.0% and MDWG: 0.02 ± 0.00g.d−1). Of the by-products, corn bran resulted in the best mean daily weight gain (0.09 ± 0.01g.d−1). A significant positive correlation of the dietary dry matter (beta: 0.98), lipid (beta: 0.99), protein (beta: 0.85) and energy (beta: 0.98) levels with the mean daily weight gain was also observed.