Effects of acute and chronic toxicity of unionized ammonia on mud crab, Scylla serrata (Forsskal, 1755) larvae

Abstract

While the eiects of ammonia on ¢sh and prawn lar- vae are well documented, little is known of its eiect on mud crab (Scylla serrata) (Forsskl, 1755) larvae. Two experiments were conducted in 5 L hemispheri- cal plastic bowls, containing 3 L of ultra-¢ltered and settled seawater and various larval stages of mud crab to (1) determine the acute median lethal concen- tration (LC50) of unionized ammonia and (2) to deter- mine the chronic eiects of unionized ammonia on survival and percentage moulting to zoea and mega- lop stages. The larval stages that exhibited the highest toler- ance to ammonia over 24 h were zoea 1 (LC50 of 4.05 mg L 1 of unionized ammonia) and zoea 5 (LC50 of 6.64 mg L 1 of unionized ammonia). The megalop stage had the lowest total ammonia LC50 at both 24 and 48 h, making it the larval stage most susceptible to total ammonia. Exposure to 6.54 mg L 1 of unionized ammonia resulted in 100% death of all larvae within 24 h. The tolerance of S. serrata larvae to total ammonia did not appear to increase with ontogenetic development. The re- sults indicate that the concentrations at which total ammonia produces an acute or chronic response in mud crab larvae are far higher than those ex- perienced in current larval production systems (0^0.5 mg L 1 of total ammonia) used as industry standards in Australia.