Acute ammonia toxicity during early ontogeny of ide Leuciscus idus (Cyprinidae)

Acute ammonia toxicity was investigated in four developmental stages of the juvenile ide, Leuciscus idus: 1, 10, 20 and 30 days after the first feeding. Mean (+/- SD) total length of the larvae was 8.5 +/- A 0.3, 15.7 +/- A 0.7, 23.0 +/- A 2.0 and 29.7 +/- A 2.0 mm, and standard weight was 1.6 +/- A 0.3, 9.2 +/- A 5.5, 94.9 +/- A 31.0 and 196.0 +/- A 31.7 mg, respectively. The larvae used for toxicity tests were reared in the experimental, closed recirculating system. Groups of fishes (n from 7 to 10; in respect of fish size) were exposed to the ammonium chloride solutions in 1-L glass units. Water temperature was 25 +/- A 0.1 A degrees C for both the rearing and the toxicity tests. pH was not adjusted and ranged between 8.4 and 8.7. The ammonium chloride solutions were renewed every 12 h. At the same time, dead larvae were counted and removed, and the pH and temperature measurements were taken. Each acute toxicity test duration was 96 h, and lethal concentration LC1, LC50 and LC99 values were calculated for 24, 48, 72 and 96 h. The susceptibility of the ide larvae to ammonia decreased linearly with age up to 20th day and surprisingly increased during the next 10 days. The LC50 (48 h) values ranged from 0.27 mg L-1 of unionized ammonia nitrogen for 1 day after the first feeding (AFF) larvae to 1.42 mg L-1 at day 20 after first feeding. The LC50 (48 h) for 30 days AFF was as high as 0.67 mg L-1. The critical level of the unionized ammonia nitrogen for ide larvae was suggested as 0.21 mg L-1.