No abstract

Nitrite is toxic to fishes and is often encountered in recirculation aquaculture systems. Accordingly, the nitrite tolerance of potential aquaculture candidates needs to be assessed before the fish can be farmed in land-based recirculation systems. In the present work, we studied the susceptibility of the marbled rabbitfish Siganus rivulatus to nitrite. In the first experiment, we placed fish at 0, 40, 50, 60, 70, 80, 90, 100, 110, 120 and 130 mg l-1 NO 2-N and evaluated 96 h LC 50. In the second experiment we measured survival and growth of fish reared at 0, 10, 20, 30, 40, and 50 mg l-1 NO 2-N for eight weeks. Blood parameters of fish in the various treatments were also measured and gill histology studied. Finally, methemoglobinemia in fish reared at various nitrite conditions was assessed. The NO 2-N 96 h LC 50 of S. rivulatus juveniles was 105 mg l-1. In the growth experiment, fish mortality was greater than in the control at NO 2-N concentrations 30 mg l-1 and greater. Growth in all treatments was less than in the control but there were no significant differences among treatments. Aqueous nitrite affected various hematological parameters such as hematocrit and total hemoglobin. Compared to other aquacultured marine fishes, the marbled rabbitfish is considered tolerant to environmental nitrite.

Marine fish are an excellent source of dietary protein and omega-3 highly unsaturated fatty acids (n-3 HUFA). Various researchers claim that wild caught fish are healthier to consume than aquacultured fish. The assumption is that the diet of the wild fish is healthier and that translates to humans consuming the fish. The spinefoot rabbit fish is an herbivorous marine fish with a healthy fatty acid profile. Because diet can significantly influence the fatty acid profile of fish, we tested the effect of dietary non-marine lipids on rabbitfish proximate composition and fatty acid profile. Spinefoot rabbitfish juveniles were maintained in 50L glass tanks connected to a recirculating system. Fish were offered one of four dietary treatments with three replicate tanks per treatment. Three feeds were formulated to contain lipids with various fatty acid profiles. One diet was formulated with fish oil (Rich in EPA and DHA), one with linseed oil (Rich in alpha linolenic acid, ALA) and the third with linseed oil supplemented with DHA. Additionally, a commercial feed was tested as a reference and all results were compared to those of fish from another experiment that were reared using a high protein and lipid commercial diet. Results show that flesh of wild rabbitfish does not contain significantly more EPA and DHA than flesh of fish offered diets rich in ALA. Flesh of rabbitfish that consumed EPA and DHA in their diets contained significantly more of these two n-3 HUFA than flesh of wild fish. The present study demonstrates that consumption of aquacultured rabbitfish is as beneficial as, if not more beneficial than consumption of wild caught fish.