Marine teleosts have extracellular fluids less concentrated than their environment, resulting in continual water loss, which is compensated for by drinking, with intestinal water absorption driven by NaCl uptake. Absorption of Cl- occurs in part by apical Cl-/HCO3 - exchange, with HCO3- provided by transepithelial transport and/or by carbonic anhydrase-mediated hydration of endogenous epithelial CO2. Hydration of CO2 also liberates H+, which is transported across the basolateral membrane. In this study, gulf toadfish (Opsanus beta) were acclimated to 9, 35 and 50 ppt. Intestinal HCO3- secretion, water and salt absorption, and the ensuing effects on acid-base balance were examined. Rectal fluid excretion greatly increased with increasing salinity from 0.17±0.05 ml kg -1 h-1 in 9 ppt to 0.70±0.19 ml kg-1 h-1 in 35 ppt and 1.46±0.22 ml kg-1 h-1 in 50 ppt. Rectal fluid composition and excretion rates allowed for estimation of drinking rates, which increased with salinity from 1.38±0.30 to 2.60±0.92 and 3.82±0.58 ml kg-1 h-1 in 9, 35 and 50 ppt, respectively. By contrast, the fraction of imbibed water absorbed decreased from 85.9±3.8% in 9 ppt to 68.8±3.2% in 35 ppt and 61.4±1.0% in 50 ppt. Despite large changes in rectal base excretion from 9.3±2.7 to 68.2±20.4 and 193.2±64.9 μmol kg-1 h-1 in 9, 35 and 50 ppt, respectively, acute or prolonged exposure to altered salinities was associated with only modest acid-base balance disturbances. Extra-intestinal, presumably branchial, net acid excretion increased with salinity (62.0±21.0, 229.7±38.5 and 403.1±32.9 μmol kg-1 h-1 at 9, 35 and 50 ppt, respectively), demonstrating a compensatory response to altered intestinal base secretion associated with osmoregulatory demand.
- Drinking rate
- Fractional water absorption
- HCO secretion
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)
- Agricultural and Biological Sciences (miscellaneous)