Ammonia toxicity to endemic fish (Rasbora maninjau) of Lake Maninjau as a reference for water quality guidelines

Abstract

Unionized ammonia (NH3) is highly toxic to freshwater organisms. Yet, most of the available toxicity data on NH3 were predominantly generated from temperate regions, while toxicity data on NH3 derived from tropical species were limited. Bada (Rasbora maninjau) as an endemic fish in Lake Maninjau-West Sumatra, has an important economic value for local communities. They live in clearwater with sand to gravel lake/river beds. The catch of R. maninjau is decreasing along with the decline of the water quality. Nowadays, the water quality of Lake Maninjau is declining as the effect of organic wastes from domestic sources and floating cage aquaculture. Therefore, the information about toxicity of ammonia in fish is important as a management tool for fish conservation. This research was aimed to find the LC50 value of ammonia in R. maninjau. A static acute toxicity test was conducted for 96 hours. Mortality was recorded for calculating LC50-96h, No Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC). Values of LC50-96h, NOEC and LOEC were 29.92 mg/L TAN or 0.7 mg/L NH3, 27 mg/L TAN or 0.63 mg/L NH3, and 38 mg/L TAN or 0.89 mg/L NH3, respectively. Maximum Acceptable Toxicant Concentration (MATC) of ammonia to Bada was 32 mg/l TAN or 0.59 mg/l NH3. The acute toxicity result showed that ammonia concentration affects the mortality of R manijau for 96 hours. The information about ammonia toxicity data will be used as a water quality guideline in Lake Maninjau.