Acute and chronic effects of ammonia in the South African abalone, Haliotis midae Linnaeus (Mollusca)

Toxicity of ammonia, which can reach toxic levels in aquaculture systems, was investigated for Haliotis midae. Toxic FAN (free un-ionized ammonia) was estimated from TAN (total ammonia nitrogen) measurements. It was found that commonly used Nesslers and Palintest methods underestimated TAN. Tolerance of H midae to ammonia increased with increasing size, as indicated by 36 h LC50 values; farmed juvenile abalone (1 - 2.5 cm shell length) had the smallest LC50 of 9.8 f,lg rl FAN, whereas LC50 was 12.9 f,lg rl FAN in wild cocktail abalone (5 - 8 cm), and 16.4 f,lg rl FAN in wild brood stock abalone (10 - 15 cm). H midae was found to acclimatize to ammonia (LC50 14.8 f,lg rl FAN) at sub-lethal concentrations, with this LC50 value for acclimatized wild cocktail-size abalone being 2.0 f,lg rl FAN greater than for non-acclimatized abalone. Ammonia tolerance was greater in farmed (LC50 37.9 f,lg r I FAN) than wild (LC50 12.7 f,lg rl FAN) H midae, with a three-fold difference between the two LC50 values. Growth of farmed juvenile H midae was inhibited during chronic exposure to sub-lethal FAN (7.4 f,lg rl), with mean ± s.d. specific growth rates (0.10 ± 0.03 % dol) reduced to 59 % of that in a control group (no added ammonia) (0.24 ± 0.06 % g dol). Heat shock proteins (HSPs) and/or P- glycoprotein (P-gp) could be responsible for increasing tolerance to ammonia in H midae. Immunological assays showed increase of a ~257 kDa protein in the gills after ammonia exposure but not after heat shock, indicating the presence of P-gp in H midae. It appeared that HSP 90, HSP 70 and HSP 60 could be implicated in both temperature and ammonia tolerance, whereas HSP 27 was solely up-regulated during heat stress. Chronic effects of ammonia on farm production were assessed using two growth models, which indicated that abalone yield could be reduced to 20% of normal yield (no ammonia stress) for sustained chronic exposure. It was proposed that HSPs and/or P-gp could be used as biomarkers indicating ammonia stress in farmed animals.