Technical note Tolerance of juvenile pompano Trachinotus marginatus to acute ammonia and nitrite exposure at different salinity levels Luiza Dy F. Costa, Kleber C. Miranda-Filho, Marlon P. Severo, Luis A. Sampaio ⁎ Universidade Federal do Rio Grande, Instituto de Oceanografia, Laboratório de Piscicultura Marinha, Rio Grande-RS, CP 474, CEP 96201-900, Brazil abstract article info Article history: Received 9 November 2007 Received in revised form 18 August 2008 Accepted 21 August 2008 Keywords: Toxicity Ammonia Nitrite Trachinotus marginatus Pompano Salinity The present study was conducted to estimate the acute toxicity of unionized ammonia–nitrogen (NH 3 –N) and nitrite–nitrogen (NO 2 –N) to juvenile pompano Trachinotus marginatus (0.86 ± 0.21 g) at different salinity levels: 5, 10 (equivalent to its isosmotic point), and 30‰. Fish were acclimated to the different salinities for 10 days and fed ad libitum daily. Groups of five fishes were exposed to five concentrations of NH 3 –N and NO 2 –N for 96 h plus control groups for each salinity, where no toxicant was added. Test concentrations ranged from 0.28 to 3.53 mg NH 3 –N/L and 24.8 to 191.1 mg NO 2 –N/L with three replicates per treatment. Tests were run using a standard semi-static system with 100% daily renewal of water and toxicants. The results were based on mortality data registered in different concentrations tested, using the software Trimmed Spearman Karber method. The median lethal concentrations (LC 50 ) after 96 h of exposure to NH 3 –N were 0.66 (0.53–0.81), 1.87 (1.65–2.12) and 1.06 (0.94–1.20) mg NH 3 –N/L for 5, 10, and 30‰. The 96 h LC 50 to NO 2 –N were 39.94 (36.39–43.84), 116.68 (112.52–121.00) and 37.55 (20.91–67.44) mg NO 2 –N/L for 5, 10, and 30‰. Acute toxicity of NH 3 –N and NO 2 –N to pompano was affected by salinity. Results of the present study show that pompano reared at an isosmotic environment are less sensitive to NH 3 –N and NO 2 –N. Tolerance to NH 3 –N is compromised at reduced salinities, while toxicity of NO 2 –N is similar at 5 and 30‰. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Carangidae are highly prized fish and are being considered for aquaculture (Craig, 2000). The pompano Trachinotus marginatus is found in estuaries and coastal waters along the Western Atlantic Coast, from Rio de Janeiro (Brazil) to Uruguay (Menezes and Figueiredo, 1980). Pompano are euryhaline, they tolerate a wide range of salinity, between 7 and 58‰, after acute exposure of individuals acclimated to seawater (35‰)(Sampaio et al., 2003), but after gradual exposure to diluted seawater, pompano can cope with even lower salinities. The protein requirement of carnivorous fish is high, which is likely to result in elevated ammonia excretion levels (Carter et al., 1998). The buildup of ammonia also leads to an increase on nitrite concentration, through mineralization of organic compounds by heterotrophic bacteria (Kamstra et al., 1996). Both unionized ammonia–nitrogen (NH 3 –N) and nitrite–nitrogen (NO 2 –N) can reach toxic levels for cultured fish, and especial attention is needed when high stocking densities are employed. Acute and chronic toxicity of NH 3 –N and NO 2 –N have been determined for a number of freshwater finfish species (Lewis and Morris, 1986; Tomasso, 1994; Randall and Tsui, 2002; Tomasso and Grosell, 2005). However, only limited information currently exists with respect to marine species (Wajsbrot et al., 1993; Bianchini et al.,1996; Rodrigues et al., 2007), including Florida pompano Trachinotus carolinus (Weirich and Riche, 2006a). The salinity equivalent to the isosmotic point of several fish species ranges from 10 to 12‰ (Sampaio and Bianchini, 2002). It is believed that when exposed to their isosmotic point, fish can spare energy for other processes, because the costs related to osmoregulation are minimized. Increasing salinity has been shown to minimize the toxic action of NH 3 –N and NO 2 –N for several species (Sampaio et al., 2002; Weirich and Riche, 2006a,b). The purpose of the present study was to evaluate the acute tolerance of juvenile pompano to ammonia and nitrite exposed to three environmental conditions: hypoosmotic (5‰), isosmotic (10‰) and hyperosmotic (30‰). 2. Materials and methods Juvenile pompano were captured during the summer along the surf zone at Cassino Beach, Rio Grande/RS, Southern Brazil (32° 12' S, 52° 10' W) and transported to the Laboratory of Mariculture of the Federal University of Rio Grande (FURG). They were acclimated for two weeks in one 1000 L tank filled with seawater, with salinity similar to the collection site (33‰), in a flow-through system. They were then divided in three groups (hypo-, iso-, and hyperosmotic exposure experiments) and transferred to 200 L tanks, where salinity was 30‰. Salinity for the hyperosmotic group remained constant thereafter, but it was gradually reduced (5‰/day) for the two other Aquaculture 285 (2008) 270–272 ⁎ Corresponding author. Tel.: +55 53 32368131; fax: +55 53 32368042. E-mail address: sampaio@mikrus.com.br (L.A. Sampaio). 0044-8486/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2008.08.017 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online