FECUNDITY OF AN AFRICAN CICHLID Pseudotropheus zebra IS INCREASED AS A RESULT OF INCREASING ENVIRONMENTAL SALINITY.
Malawi cichlids are a widely cultured freshwater ornamental fish within the Florida aquaculture industry. However, competition from suppliers outside the United State has decreased the market share of domestic Malawi producers making fecundity of existing domestic brood stock particularly important. Additionally, international cichlid imports are often imported at reduced cost making competition in this market harder for US farmers. Cost-effective production strategies directed at increasing fecundity are clearly needed, however many fish farmers in Florida do not command sufficient resources to pursue research using alternative production methods and often rely on increased stocking densities to compensate for other limited resources such as production space, water treatment, and short-falls in reproduction and growth related to stressed fish.
Stress-related osmoregulation under hypoosmotic conditions in freshwater fish consumes dietary energy that would otherwise be available for growth and reproduction. While growth and reproduction has been investigated using food fish including several species of tilapia, many of those studies were focused on growth in water which was not isoosmotic. It has been demonstrated that fish raised under isosmotic conditions exhibit increased growth, however fecundity of fish raised under similar conditions has received less attention and has not been investigated in Malawi cichlids. Therefore, a preliminary study was conducted investigating the effects of increased salinity on Pseudotropheus zebra fecundity within a recirculating system housing Malawi cichlids.
P. zebra were placed into two parallel recirculating systems consisting of 3, 100 gallon tanks each. Water in the first system was treated with sea salt and maintained at a concentration of
6 ppt while the water in the second system was not treated with salt. Brood fish weighing 60g each were stocked at a ratio of 1 male fish to 4 female fish. Culture water was maintained at 29°C and water quality parameters including ammonia-N, nitrite-N, and pH, were monitored daily and maintained within the normal range for this species. Fish were fed to apparent satiation twice daily using a commercial diet formulated to meet the nutrient needs of ornamental fish. Each week eggs were collected by hand from the buccal cavity of females. Eggs were examined to evaluate overall condition and each clutch of eggs was counted to determine fecundity.
Results from the preliminary study indicated that addition of salt at concentrations below isosmotic (6 ppt) increased fecundity by 3% in a Malawi cichlid P. zebra, therefore in the present study the effects of an isoosmotic environment on fish fecundity and fry hatch rate and survival were measured in the same species. We anticipate that maintaining a culture environment near isoosmotic conditions will increase fecundity of this species.