The European catfish Silurus glanis has been cultivated in extensive ponds in central and Eastern Europe in association with carps for more than 100 years. The total production of S. glanis in aquaculture from ten European countries (Austria, Bulgaria, Croatia, Germany, France, Hungary, Greece, Macedonia, Poland, Czech Republic and Romania) was 602 t in 1993 and presently is about 2000 t. Production is increasingly from intensive pond culture or in heated/geothermal waters. The flesh is white, boneless, easy to prepare, and low in fat (6 to 8%). The taste is mild but is subject to off-flavour. The fish are filleted (yields about 40% without skin) and the flesh is cut into steaks or smoked). During the last 10 years, research in Czech Republic, France and other European countries have developed technologies for artificial reproduction, evaluated population genetics and addressed problems of conservation. Growth is higher in males and research is in progress to produce triploids fish. While propagation techniques have progressed, production remains low and the cost of production is still high. Thus availability is low and the product remains poorly known.

Two experiments were developed in France to assess whether growth and processing traits differ for males and females in the European catfish, Silurus glanis. In the first experiment, fish were raised from 5 to 200 g in a pond for 7 months. A significant sex effect is demonstrated in males for live weight at the end of the experiment (males 147.5 ± 5.4 g vs females 132.9 ± 4.9 g) and head index (males 20.6 ± 0.1 % vs females 21.2 ± 0.1 %, P < 0.05). In the second experiment, fish were raised from 885 ± 196 g to 2 266 ± 418 g in a recirculated system at 20.7 ± 1.4 °C for 120 days. A differential growth between the sexes is also registered. Males are heavier and longer (+ 357 g or + 17.0 % and + 6.2 % in length at day 120) and present a higher gutted weight and yield (+ 367 g or + 18.7 %; 95.0 ± 0.9 % vs 93.8 ± 1.8 %) and fillet weight (+ 233 g or + 20.9 %) than females after slaughter.

Nous étudions les principes généraux qui expliquent comment les animaux aquatiques assurent leurs échanges gazeux (O2 et CO2) en fonction d'une part, de leurs besoins physiologiques et d'autre part, des changements des caractéristiques physico-chimiques du milieu. Cette synthèse, basée sur le cas exemplaire du silure glane, résume nos observations sur les mécanismes qui permettent à des animaux aquatiques physiologiquement très différents de s'adapter aux variations d'oxygénation du milieu ambiant. Le but de la stratégie d'adaptation est de maintenir constant l'état d'oxygénation du sang, à une faible valeur de pression partielle d'O2 (Po2) dans le sang artériel, indépendamment des variations de Po2 dans l'eau. Chez le silure, la valeur la plus couramment mesurée de Po2 dans le sang artériel est 2 kPa (15 mm Hg) pour des variations de Po2 dans l'eau comprises entre 3 et 40 kPa (1,5 à 20 mg.1−1 à 13 °C). Ce qui est aussi particulier chez cet animal est que toute l'adaptation est réalisée par la ventilation : il n'y a aucun changement de débit cardiaque, ni de modification de l'affinité de l'hémoglobine pour l'oxygène via le pH sanguin. La valeur de Po2 inspirée jusqu'à laquelle la consomation d'O2 peut être assurée pendant au moins 24 h à 13 °C est 2 à 3 kPa. Nous pensons que chez le silure cette valeur de Po2 est largement indépendante de la température car chez des animaux aussi divers que la carpe, la truite ou l'écrevisse (adaptés au laboratoire à différentes températures comprises entre 10 et 23 °C) la valeur de Po2 critique est aussi égale à 2-3 kPa indépendamment de la température. Toutes les mesures que nous citons ont été faites chez des animaux à jeun au laboratoire mais le principe du « fonctionnement » de très nombreux animaux aquatiques avec de faibles valeurs de Po2 artériel, indépendamment de la température, a été vérifié dans le milieu naturel. Nous n'avons actuellement aucune idée sur les capacités du silure dans un élevage intensif, en particulier lorsque des pathologies s'y développent. Néanmoins, il est clair que les capacités maximales d'adaptation du silure face à l'hypoxie sont très grandes.

Survival of Silurus glanis ovulated oocytes (ova) measured by the capacity of normal development i.e. percentage of normal and abnormal hatched larvae after in vivo and in vitro storage and exposure to sperm activating or immobilizing solutions and urine was studied. In the case of ovulated oocytes left in the ovaries, total hatching and abnormal hatched larvae (in % of hatching) were respectively 74 and 8.2% immediately after ovulation, 77 and 8.6% after 2 h, 54 and 18% after 4 h, and 38 and 50% after 6 h of storage. Four and 6 h stay of ovulated oocytes in ovaries resulted in a significant increase of abnormal hatched larvae (p < 0.01). For the ova stored in vitro, the capacity to undertake a full embryonic development after fertilization was not significantly changed either after 8.5 h at 19 °C or 3.5 h at 25 °C; there was no ova survival at all after 3.5 h storage at 8 °C, 12 h at 19 °C and 8.5 h at 25 °C. There was a significant increase of abnormal larvae after 3.5 h at 25 °C (74%, p < 0.001) and after 8.5 h at 19 °C (37%, p < 0.05). Exposure of non inseminated ova to water buffered to pH 7.0 (5 mM Tris-HCl) to sperm activating solution (17 or 41 mM NaCl, 5 mM Tris-HCl, pH 8.0) or to immobilizing solution (200 mM NaCl, 30 mM Tris-HCl, pH 7.0) resulted in a regular and rapid decrease of their capacity of development; this was 10% of normal hatched larvae within 4 min in water, and within 6-8 min in the NaCl solutions. A similar situation was observed after exposure to urine with a loss of embryonic development of 30% within 3 min. These results indicate that all steps of the whole procedure of gamete collection and artificial insemination should be carried out rapidly as soon as possible after ovulation.