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 NO2-N and evaluated 96 h LC50. In the second experiment we measured survival and growth of fish reared at 0, 10, 20, 30, 40, and 50 mg l-1 NO2-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 NO2-N 96 h LC50 of S. rivulatus juveniles was 105 mg l-1. In the growth experiment, fish mortality was greater than in the control at NO2-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.
Highlights
As locations suitable for aquaculture become scarcer and more costly and diseases more prevalent, modern aquaculture facilities are opting for intensive and biosecure rearing systems, mostly Recirculation Aquaculture Systems (RAS)
We evaluated the effects of chronic exposure of S. rivulatus to nitrite on survival, growth performance, hematological and biochemical parameters
All fish survived for 96 h in the treatments containing nitrite concentrations from 0 to 60 mg l-1
Summary
As locations suitable for aquaculture become scarcer and more costly and diseases more prevalent, modern aquaculture facilities are opting for intensive and biosecure rearing systems, mostly Recirculation Aquaculture Systems (RAS). Excessive nitrite levels in culture systems can cause depressed growth [4], increased susceptibility to disease, and eventual mortality [5] This competition with chloride decreases the detrimental effects of nitrite in marine waters and makes nitrite more dangerous in freshwater aquaculture. Marbled rabbitfish Siganus rivulatus is a euryhaline, herbivorous marine fish widely distributed along the Eastern Mediterranean and East Indian Ocean [25] This teleost is a valuable fishery species that is relatively easy to farm and considered of great potential for warm-water aquaculture diversification [26,27,28]. We determined levels of total hemoglobin and methemoglobin in the fish upon chronic nitrite exposure
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