Pre-acclimation to low ammonia improves ammonia handling in common carp (Cyprinus carpio) when exposed subsequently to high environmental ammonia

• Published in: Aquatic toxicology 2016-11, Vol.180, p.334-344
• Main Authors: Shrivastava, Jyotsna, Sinha, Amit Kumar, Datta, Surjya Narayan, Blust, Ronny, De Boeck, Gudrun
• Format: Article
• Language: English
• Subjects: Acclimatization; Ammonia - metabolism; Ammonia - toxicity; Ammonia acclimation; Ammonia flux; Animals; Biomarkers - metabolism; Carps - metabolism; Cyprinus carpio; Dose-Response Relationship, Drug; Freshwater; Gene expression; Inactivation, Metabolic; Rhesus (Rh) glycoproteins; Survival; Survival Rate; Toxicity Tests; Up-Regulation; Water Pollutants, Chemical - metabolism; Water Pollutants, Chemical - toxicity
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2016.10.017

•We examined if pre-exposure with low ammonia dose (0.27mM) can facilitate fish to tolerate (sub)lethal ammonia exposure.•Pre-exposure to ammonia prolonged the survival time during subsequent lethal ammonia (2.7mM) challenge.•Pre-acclimation to ammonia facilitated ammonia excretion rate in response to high ammonia (1.35mM) exposure.•The expression of Rhcg isoforms, NHE-3 and NKA genes were also up-regulated in response to ammonia pre-exposure.•The potential effect of ammonia pre-acclimation was detected for 3–7days but was attenuated by 14days. We tested whether exposing fish to low ammonia concentrations induced acclimation processes and helped fish to tolerate subsequent (sub)lethal ammonia exposure by activating ammonia excretory pathways. Common carp (Cyprinus carpio) were pre-exposed to 0.27mM ammonia (∼10% 96h LC50) for 3, 7 and 14days. Thereafter, each of these pre-exposed and parallel naïve groups were exposed to 1.35mM high environmental ammonia (HEA, ∼50% 96h LC50) for 12h and 48h to assess the occurrence of ammonia acclimation based on sub-lethal end-points, and to lethal ammonia concentrations (2.7mM, 96h LC50) in order to assess improved survival time. Results show that fish pre-exposed to ammonia for 3 and 7days had a longer survival time than the ammonia naïve fish. However, this effect disappeared after prolonged (14days) pre-exposure. Ammonia excretion rate (Jamm) was strongly inhibited (or even reversed) in the unacclimated groups during HEA. On the contrary, after 3days the pre-exposure fish maintained Jamm while after 7days these pre-acclimated fish were able to increase Jamm efficiently. Again, this effect disappeared after 14days of pre-acclimation. The efficient ammonia efflux in pre-acclimated fish was associated with the up-regulation of branchial mRNA expression of ammonia transporters and exchangers. Pre-exposure with ammonia for 3–7days stimulated an increment in the transcript level of gill Rhcg-a and Rhcg-b mRNA relative to the naïve control group and the up-regulation of these two Rhcg homologs was reinforced during subsequent HEA exposure. No effect of pre-exposure was noted for Rhbg. Relative to unacclimated fish, the transcript level of Na+/H+ exchangers (NHE-3) was raised in 3–7days pre-acclimated fish and remained higher during the subsequent HEA exposure while gill H+-ATPase activities and mRNA levels were not affected by pre-acclimation episodes. Likewise, ammonia pre-acclimated fish with or without HEA exposure displa