Reproduction of Zingel asper (Linnaeus, 1758) in controlled conditions: an assessment of the experiences realized since 2005 at the Besançon Natural History Museum
The Zingel asper or apron is one of Europe’s most threatened freshwater fish (classified as critically endangered by the International Union for Conservation of Nature, IUCN). It is also listed in appendices II and IV of the European Habitats Directive (1992) and in appendices II and III of the Berne Convention (1979). The geographical distribution of this percid, endemic to the Rhône basin, is extremely limited, making it particularly vulnerable. Since 2005, the Besançon Natural History Museum has been involved in conservation programmes (LIFE Apron II and a national action plan) to improve the knowledge on its ex situ reproduction, the aim being to produce individuals with which to conduct experimental studies (toxicity tests, design of fish passes, etc.), carry out public presentations (aquariums, nature reserves, etc.) and implement pilot reintroduction schemes, without having to systematically take samples from the natural environment. Innovative devices were designed in the Besançon Citadelle Aquarium to enable replication of complete reproduction cycles in artificial conditions. Control of thermal and zootechnical parameters associated with the development of “artificial spawning grounds” have allowed us to understand the different phases involved in reproducing and maintaining this species in captivity. We were able to observe numerous behaviours, which have never been seen in natural environments, in particular during spawning and early life stage development phases. Several experiments were conducted to study how hatching rates varied according to the duration of the winter cold period, known as “vernalization”, applied to broodstock. Hatching rates in the order of 80% were obtained with broodstock subjected to a cold period of 120 days at 5°C, from the beginning of November to the end of February. In contrast, hatching rates dropped rapidly for groups of broodstock subjected to vernalization periods of less than 90 days, and with a cold period of only 30 days, the eggs deteriorated before hatching. A precise annual thermal cycle has therefore been identified, corresponding to the different life phases of Z. asper in captivity. A particular focus of our work was on breeding of fry to ensure that they achieve survival rates in the order of 80% during the first month, and 90% the following month. The results of these experiments have supported other studies and more than 26,000 juveniles have been released into the Drôme River. Regular genetic monitoring of this reintroduced population has allowed us to ensure that they are reproducing naturally. Z. asper born in captivity are also widely used in initiatives to raise public awareness (exhibitions, etc.). To date, the Z. asper breeding programme in the Besançon Natural History Museum is the only one of its kind for this percid, but the high sensitivity of broodstock to the intensity and duration of the vernalization period should raise concerns about the sustainability of its populations in the face of climate change.