The Physiological Adaptations of the Lahontan Cutthroat Trout (Oncorhynchus clarki henshawi) following Transfer from Well Water to the Highly Alkaline Waters of Pyramid Lake, Nevada (pH 9.4)

Abstract

Salmonids experience severe disturbances in the excretion and internal regulation of ammonia, acid-base balance, and ionoregulation when challenged with alkaline pH. We followed the responses of a high-pH-tolerant salmonid, the Lahontan cutthroat trout (Oncorhynchus clarki henshawi)for 72 h after transfer from pH 8. 4 well water into the alkaline water (pH 9. 4) of Pyramid Lake, Nevada. Fish that had been living in Pyramid Lake for 3 wk, 5 wk, and 2 yr were also examined. A combined metabolic and respiratory alkalosis (negative metabolic acid load [AH+] and decreased arterial CO2 tension [Paco2], respectively) occurred initially. The metabolic component was corrected within 24 h, but the respiratory component persisted for up to 5 wk. Transfers also resulted in an immediate 70% reduction in the ammonia excretion rate (J,,m) and a 30% increase in total plasma ammonia (Tm,,). The Tm,,,m was corrected within 3 d, but Jamm remained depressed, which indicates reduced ammonia production rates. Because the urea excretion rate (J,,rea) did not change, the contribution of Jrea to total N excretion increased from 10% in well water to 25% in fish acutely and chronically exposed to lake water. Liver enzyme activities indicated that the pathway for urea production was uricolysis, not the ornithine-urea cycle. Branchial chloride cell fractional surface area increased in lake water, and this may have counteracted the base load by promoting base equivalent excretion via Cl-/HCOj exchange. Plasma Na+ and Cl-levels were slightly higher in Pyramid Lake water. We conclude that the Lahontan cutthroat trout are able to survive in

Na+ and K+ body levels and survival of fingerlings of Rhamdia quelen (Siluriformes, Pimelodidae) exposed to acute changes of water pH.

“…A decrease in Na + levels was also determined in Perca flavescens, Notropis cornutus, and Salmo gairdneri exposed to pH 4.00 (FREDA & McDONALD, 1988) and in Salmo salar and Alosa pseudoharengus living in acidic rivers (LACROIX, 1985). Transfer of Oncorhynchus clarki henshawi specimens from water at pH 9.4 to pH 10.0 reduced Na + and K + levels of the muscle (WILKIE et al, 1994). Plasma Na + and Cl -levels also decreased in Oncorhynchus mykiss transferred to soft water at pH 10.0 (YESAKI & IWAMA, 1992) or buffered water at pH 10.5 (McGEER & EDDY, 1998).…”

“…Several studies have dealt with the survival of fishes in relation to pH changes, but all experiments analyzed the survival of a given species at acidic (GONZALEZ & DUNSON, 1987;FREDA & McDONALD, 1988; VAN DIJK et al, 1993) or alkaline pH (WILKIE et al, 1993(WILKIE et al, , 1994, and not at both extremes of pH. Several teleost species tolerate acute exposure up to pH 4.5 in soft water, but at pH 4.0 some species, like Catostomus commersoni, die within 48h (FRASER & HARVEY, 1984).…”

“…Survival at lower pH in soft water is obtained only for species that usually live in acidic habitats like the Rio Negro in the Amazon region (GONZALEZ, 1996). Comparisons of survival at alkaline pH are complicated by the fact that some experiments were carried out in hard water (YESAKI & IWAMA, 1992) or alkaline-saline water (WILKIE et al, 1993(WILKIE et al, , 1994. Salmonids in general can survive some days in soft water at pH 9.5, but a pH of 9.7 is lethal within one day (ALABASTER & LLOYD, 1982).…”

“…Oscillations in water pH over this range may be due to the abundance of phytoplankton or the presence of high concentrations of dissolved HCO 3 -and CO 3 2-salts (alkaline pH) or of mineral and organic acids (acidic pH) (WILKIE & WOOD, 1996;ARANA, 1997). Most fish species survive acute exposure (a few days) to pH 4.5 to 9.0 (FREDA & McDONALD, 1988; VAN DIJK et al, 1993) but some species can resist even pH 3.5-4.4 (GONZALEZ & DUNSON, 1987) or a pH near 10.0 (WILKIE et al, 1993(WILKIE et al, , 1994. Survival in acidic waters seems to be mainly related to the ability to prevent loss of Na + (FREDA & McDONALD, 1988) while adaptation to alkaline waters implies adjustments to nitrogen waste metabolism and excretion patterns (WILKIE & WOOD, 1996).…”

Acclimation Improves Short-Term Survival of Hatchery Lahontan Cutthroat Trout in Water From Saline, Alkaline Walker Lake, Nevada

“…Lahontan cutthroat trout challenged with water from saline, alkaline Pyramid Lake appear to adapt quickly to increased pH by quickly increasing the number and size of chloride cells in their gills, where chloride anions may be exchanged for HCO 3 2 (mitigated by ion uptake in the gills) to maintain lower internal pH than the alkaline waters (Wilkie et al 1994). Acid-base regulation is important in maintaining safe internal ammonia concentrations.…”