Physiological adaptations of rainbow trout to chronically elevated water pH (pH = 9.5)

Abstract

Recent investigations have demonstrated that rainbow trout cope with acute high pH (pH > 9.0) exposure (lasting 3–8 days) through their ability to counteract high‐pH‐induced disturbances to ammonia excretion (JAmm), acid‐base homeostasis, and electrolyte balance. In the present investigation our goal was to establish how these physiological processes were modulated during chronic (28‐day) high pH (pH = 9.5) exposure. Chronic high pH led to minimal mortality, and there were no long‐term changes in stress indicators levels, such as cortisol or glucose. JAmm was initially reduced by 40% at high pH but rapidly recovered and fluctuated around control rates, thereafter. Decreased JAmm was associated with an initial 2.5‐fold increase in plasma ammonin concentrations (TAmm), followed by a return toward pre‐exposure levels after 3 days. Overall, plasma TAmm was slightly higher (40–80%) in the treatment fish, and this likely led to plasma PNH3s that were sufficient to sustain JAmm at high pH. White muscle TAmm stores were also chronically elevated, by 50–100%. There was a transient, twofold elevation of JUrea immediately following high‐pH exposure, but by 3 days JUrea had returned to control rates and stabilized thereafter. Plasma ion balance was well maintained at high pH, despite a chronic depression of Na+ influx. Even though there was a persistent respiratory alkalosis at alkaline pH, blood pH was effectively regulated by a simultaneous metabolic acid load, which was not associated with increased lactic acid production. White muscle intracellular pH (pHi) was unaltered during high pH exposure. We conclude that the long‐term survival of rainbow trout in alkaline environments is facilitated by higher steady‐state internal ammonia concentrations, the development of a sustained, compensatory metabolic acidosis which offsets decreased plasma PCO2, and the effective regulation of plasma electrolyte balance. © 1996 Wiley‐Liss, Inc.

Nitrogenous waste excretion by the larvae of a phylogenetically ancient vertebrate: the sea lamprey (Petromyzon marinus)

“…Total ammonia and urea concentrations in the water were determined as described by Wilkie et al (1996). Plasma ammonia was determined enzymatically (GDH), using a commercial kit (Sigma).…”

The relationship between NMDA receptor function and the high ammonia tolerance of anoxia-tolerant goldfish

“…Levi et al, 1974), because the increases in urea excretion were relatively modest. Similar declines in urea were reported in the muscle of rainbow trout exposed to alkaline water (Wilkie et al, 1996), and in the plasma of Atlantic salmon (Salmo salar) exposed to ammonia (Knoph and Thorud, 1996). It seems unlikely that the unloading of such relatively modest amounts of urea by ammoniaexposed goldfish would play a role in ammonia detoxification given the 10-20-fold higher concentrations of ammonia in the muscle of the fish at HEA.…”

Characterisation of chemosensory trigeminal receptors in the rainbow trout,Oncorhynchus mykiss: responses to chemical irritants and carbon dioxide

“…For this reason, data for the two receptor types were pooled for the second experiment. Chemically responsive receptors did not respond to any of the innocuous chemicals -alarm pheromone, ammonium chloride, bile, freshwater and sodium bicarbonate (Holliman, 1993;Hara, 1994;Sorensen and Caprio, 1998;Craig and Laming, 2004;Galea, 2002;Wilkie et al, 1996) -suggesting that they have a purely nociceptive function. These mechanochemical receptors responded to between one and five (all of the potentially noxious agents tested) types of agent.…”

“…Ammonium chloride at high concentrations is toxic to teleosts, but concentrations between 0.02 and 1.0mgl -1 were tested -levels that are assumed to be non-irritating to trout (Hedtke and Norris, 1980;Holliman, 1993;Saha and Ratha, 1994;Craig and Laming, 2004). Sodium bicarbonate was also tested (at 0.1, 0.5 and 1.0moll -1 ) because alkaline waters can have deleterious effects on fish physiology but several studies have shown that rainbow trout can adapt and survive in high pH environments, an event that can occur naturally in eutrophic lakes (Yesaki and Iwama, 1992;Wilkie and Wood, 1994;Wilkie et al, 1996). High pH has not been reported to excite nociceptors in other vertebrates (Galea, 2002;Woolf and Ma, 2007;Dafny, 2010).…”