Feeding strategies and nutritional physiology in early life of clariid catfishes

In many countries of Africa and Asia, catfishes belonging to the genus Clarias, are commercially important. Also, in Europe, Clarias farming is developing. Together with the increasing interest in the culture of these species, the need for reliable and precise hatchery techniques is strongly growing. This has led to a wide array of both extensive and intensive techniques for larval rearing. The present paper attempts to correlate the applied feeding strategies with information on the basic biology of the respective species. Catfishes of the genus Clarias (e.g. C. gariepinus, C. batrachus, C. macrocephalus pass through a larval period during which several organ systems are still developing into adult organs. This situation imposes strict limitations on the type of food during the early larval period. The African catfish, C. gariepinus, has been extensively studied with regard to biology and nutritional physiology during the larval stage. At the start of exogenous feeding, the larvae have an advanced digestive system with a functional pancreas, liver and nutrient absorption, but without a functional stomach. This is further exemplified by concurrent changes in the development of the enzymatic complex. Probably because of this advanced stage of development, feeding live food organisms is mostly practiced for a few days only and is soon replaced by wet and/or dry diets. The rearing and feeding strategies applied in commercial farms reflect the knowledge of the basic biology of the species under concern. In Africa, extensive and semi-extensive systems prevail for the culture of C. gariepinus and C. senegalensis, with larvae being raised in ponds and at the most with the natural food supplemented with trash fish and dry feed ingredients. In Asia, similar semi-extensive systems are applied in the culture of C. batrachus and C. macrocephalus, however, using more intensive nursing systems during the early larval period. Semi-intensive and intensive culture systems prevail in Indonesia, South Africa and Europe, with feeding C. batrachus and C. gariepinus with dry diets and supplements of Artemia . The periods during which these strategies are applied and the growth rates attained vary according to the species and the region. A comparative study of basic biological data on the development of C. gariepinus and C. batrachus revealed that in spite of strong differences in egg and larval size, the growth rate was quite similar for both species. Further comparison between these species indicates that differences in growth results between different species and regions may be strongly correlated with the applied feeding strategy, which may have a stronger impact on the results than species related differences