Raniculture or field harvesting ? State of the art in France

Abstract

In Europe, frogs appeared in the best culinary circles only around the 16^th ;century. During the 20^th, a strong decline is observed in certain populations under direct and indirect influences of human activities.

France is the main importer with 3000-4000 tons.year^-1 ; of deep frozen legs from Far East countries and 700-800 tons.year^-1 ;of live frogs from the Near East, that are transformed into fresh legs to gastronomic restaurants.

During recent years some countries are carrying out trials of intensive rearing with neotropical species and a recent artificial feeding. In West part of France (near Rennes town) trials began during 1980’s with local water frogs (esculenta ; complex). This complex is composed by two parental species (Rana lessonae, R. Ridibunda) and a hybridogenetic form (R. Esculenta). Pure; ridibunda; stocks are the most attractive issue for intensive rearing.

At the beginning of our trial, the females gave several clutches within a year with a high fertility. However, after a decade of rearing, fecundity and fertility became reduced, the causes of this problem being not completely identified. The juveniles are fed on pellets. After 40 days, survival rate of froglets is 92 %, and their mean size reaches 32 mm. In a green house the growing period from weaned froglets to mature adults is around 10-12 months with a production of 20-30 kg.m^-2; (thermic level between 15 and 25 °C). Any combination with lessonae; genome strongly reduces the final size.

An alternative to intensive production would be to restore natural stocks in suitable areas. Since 1986, several trials with R. temporaria have been carried out, which associate intensive rearing of tadpoles in tanks, releasing of metamorphs at a natural site (a small forest area) and control of the return of adults (return rate: 6 %) to spawning sites after two summers (strong homing effect). Discussions are conducted on the best strategy to take up in relation to laws and economic restraints in France.