Abstract
The acute toxicity of blue tilapia, Oreochromis aureus (3.28 ± 0.36 g in body weight, 61.84 ± 2.08 mm in body length) exposed to environmental un-ionized ammonia at different salinities (1, 8, 12, 16 and 20 ppt) was assessed via a series of static exposure trials. Median lethal concentrations of 24 h of exposure were calculated for each salinity. Tolerance of blue tilapia to acute un-ionized ammonia exposure was not influenced by salinity. Median lethal concentrations (24-h LC50) values were found to be 2.83, 2.26, 3.14, 3.11 and 1.93 mg/l NH3 at 1, 8, 12, 16 and 20 ppt of salinities, respectively. The results of this study indicate that using brackish water for blue tilapia culture may not be a single factor to reduce the toxicity of high ammonia. Key words: Oreochromis aureus, blue tilapia, ammonia, salinity.
Highlights
All tilapia species can live in saline waters
The experimental fishes were measured for length and weight and they were placed into the desired ammonia concentration and salinity for the 24-h period
Fresh water hardness and alkalinity were much more diffferent from that of saltwater and this did not have any influence on 24-h LC50 of un-ionized ammonia at different salinities
Summary
All tilapia species can live in saline waters. Oreochromis mossambicus is the most tolerant species and Oreochromis aureus is more tolerant than Oreochromis hornorum but red tilapia can survive even marine water.There are essentially two liming water quality factors, that is, dissolved oxygen (DO) and ammonia in aquaculture practices. All tilapia species can live in saline waters. Previous studies on Atlantic salmon showed that ammonia toxicity could be decreased with increase in DO and salinity (Alabaster et al, 1979). Another study showed that the increase in temperature reduced the acute ammonia toxicity
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