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Individual Penaeus chinensis adults (26.91 + 4.66 g) were subjected to 0.03, 5.10, 10.11 and 20.04 mg I-' ammonia-N (un-ionized plus ionized ammonia as nitrogen) in 30 ppt seawater and 25 "C. Changes in ammonia-N excretion, hemolymph ammonia-N and hemolymph protein were monitored for 1 to 24 h. Net ammonia-N uptake occurred when shrimp were exposed to 10.11 and 20.04 mg I ' ammonia-N after 4 h. Relationships among ammonia-N excretion rate, hemolymph ammonia-N, hemolymph protein, concentration of ambient ammonia-N and exposure time were determined. An increase of ammonia-N and a decrease of protein in the hemolymph of P chinensis following a 4 h exposure to ambient ammonia-N as high as 10 mg 1-' may cause catabolism of protein and amino ac~ds to balance the osmoregulation, as well as dysfunction of Na+/NH,+ exchanges. The fleshy prawn Penaeus chinensis Osbeck is a typical penaeid which matures and spawns in seawater, spends postlarval and juvenile phases in brackish water, then returns to the sea as a preadult. It is also an important penaeid currently being cultured in China, Taiwan and Korea (Chen 1990). This species can be reared at salinities ranging from 20 to 32 ppt which was considered the optimal level by Liu (1983). Ammonia, the end-product of protein catabolism, accounts for more than half of the nitrogenous waste of decapod crustaceans and is continually released. Ammonia is excreted mainly through the gill epithelium (Regnault 1987). Protein and amino acids can serve as a significant source of metabolic energy for crustaceans (Claybrook 1983). A decrease in the ambient osmotic concentration increased catabolism of amino acids, causing an increase in ammonia-N excretion (Lange 1972). Ammonia has been reported to affect osmoregulation of crustaceans (Young-Lai et al. 1991). However, there is no information concerning its effect on protein and amino acid level in the hemolymph. This study was designed to monitor hemolymph ammonia-N, hemolymph protein and ammonia-N excretion of Penaeus chinensis adults exposed to different concentrations of ammonia-N. Materials and methods. Penaeus chinensis adults obtained from Tainan Branch, Taiwan Fisheries Research Institute, Keelung, were acclimated in a holding tank for 1 wk and fed commercial shrimp feed (39 %crude protein) designed for P monodon (Tairoun Products Co., Taipei, Taiwan) once a day. Shrimp were not fed for 2 d prior to the experiment. Starved shrimp were randomly removed from the holding tank and individually transferred to a 20 1 circular plastic tank containing 10 1 of each test solution. Individual tanks were aerated through an air blower attached to an aeration stone. Only shrimp in the intermolt stage (Wassenberg & Hill 1984) were selected for the study. There were 20 treatments, 4 test solutions combined with 5 exposure times: 1, 4, 8, 16 and 24 h. For each treatment there were 5 replicates. The total number of shrimp used was 105, 5 for each treatment plus 5 for an initial control solution. Shrimp used ranged from 21.25 to 30.52 g with an average weight of 26.91 -t 4.66 g ( R k SD) and no significant difference in weight was found among treatments. In addition, 10 tanks containing aerated test solution only (duplicates for each test solution) were used as blanks. Ammonia test solutions consisting of concentrations of 0.03 (control), 5.10, 10.11 and 20.04 mg 1-' ammonia-N were prepared according to the procedure reported previously (Chen & Nan 1992). The experiment started at 09:OO h and lasted for 1, 4 , 8, 16 and 24 h under a photopenod of 12 h light: 12 h dark with a light intensity of 160 to 250 lux during the day. The concentration of ammonia-N was determined by the phenolhypochlorite method (Solorzano 1969) at the beginning and end of the experiment. Ammonia-N excretion was cal0 Inter-Research 1993 204 Mar. Ecol. Prog. Ser. 98: 203-208, 1993 Table 1. Penaeus chinensis. Mean (f SE) concentration of ammonia-N over time for blank solutions" (B) and test solutions contaming shrimp (T) Initial ammonia-N conc. (mg 1 l ) Ammonia-N concentration (mg 1.') after:

Effects of ambient ammonia on ammonia-N and protein concentrations in hemolymph and ammonia-N excretion of Penaeus chinensis