SEAF DEC/IDRC (1979) lists the following criteria for selecting fish for use in enclosures:
value of fish and market demand
hardiness (in terms of ability to adjust to high density culture, disease and hadling).
ready availability of fish seed or juvenile fish for stocking
fast growth in confined waters
availability of suitable feeds
In general in considering the suitability of the fish species, the ecological niche of the species and the biology and special requirements of the various stages of the fish should be carefully studied and the pen conditions should be suitably adjusted - or the species chosen should fit into the pen condition and if in polyculture should be combatible with the other species in the culture. Care must be taken to design the culture system to approximate natural conditions of the species recruited for culture, especially with reference to water quality, natural feeds, predators etc.
The freshwater, brackish water and marine habitats have to be considered separately and suitable species recommended.
Habitats with high natural productivity (lakes, oxbow lakes, reservoirs, rivers, swamps, mining pools etc):
Species suggested (of potential in the tropics) are:- milkfish, Chinese carps, Indian carps, mullets, Tilapia mossambica, T. nilotica, puntius gonionotus, common carp, eals, catfish etc. Clarias gariepinus the African catfish can also be tested.
In habitats with low natural productivity in freshwater bodies, species which “are not able to survive on natural productivity alone but can grow well with supplementary freding” have been suggested, e.g. Laptobarbus, Pangasius, Clarias batrachus, Oxyeleotris and among crustaceans, Penaeus spp. Macrobrachium etc. several other African species could also be included in tests.
This is a most variable environment and is considered as a more difficult environment when compared with those of freshwater and marine. The species chosen should be able to grow well in changing salinities. Despite the changes in tidal height and salinity the environment offers advantages in enclosure culture, especially in terms of protected sites.
Species of potential value are: milkfish, sea bass, mullets, siganids, sea eel; among crustaceans, Penaeus spp. and crabs. Chrysichthys mgrodigitratus and C. walkeri have been successfully tested in Cote d'Ivoire (see section 7). Brackishwater Tilapia, T. guineensis and T. melanotheron can also be value.
In this environment there are natural problems due to waves and wind as discussed, but there are protected areas in many countries around bays, coves, atolls etc. Species of demonstrated potential in the tropical areas are:
Milkfish, pompano, yellow-tail, tuna, grouper snapper, sea bass, sea bream, carangids, pomfret and among crustaceans, spiny lobsters. In the western temperate areas salmonids (especially trouts, Atlantic and Pacific salmons) and placed and turbot are of proven value.
Many of the species listed above have been proved to be of potential value in small level enclosures, especially in Cages, but several can be adopted for pen culture as well - in the pen culture natural conditions can be approximated at a better level than in the cage and the larger space would favour better growth of species, but problems of protection and harvest are more difficult in the pen than in the cage, as we have already discussed earlier (Advantages and disadvantages of pen culture).