Changes in the fatty acid composition of steelhead trout, Salmo gairdnerii Richardson, associated with parr-smolt transformation.

Fatty acids from the several lipid classes of selected steelhead trout (Salmo gairdnerii) parr and smolt tissues, previously separated by thin-layer chromatography, were analyzed by gas-liquid chromatography. The fatty acid composition of the parr was markedly different from that of the smolt; the former being characterized by relatively low amounts of polyunsaturated fatty acids and relatively high amounts of linoleic acid, much like the typical freshwater lipid pattern. The fatty acid composition of the smolt was characterized by large proportions of long-chain polyunsaturated fatty acids. Generally, the fatty acid composition of the smolt resembled the typical seawater lipid pattern. The change in fatty acid composition of the smolt is anticipatory to seawater entry and is independent of diet and water temperature. These alterations suggest that the assumption of a polyunsaturated lipid pattern during parr-smolt transformation (smoltification) is preadaptive to seawater entry.

Responses of trout gill ion transport systems to acute acidosis.

The response of rainbow trout Na+ and Cl- uptake systems to acute acidosis was tested by slow infusion of lactic acid into anaesthetized animals. Depression of blood pH by 0-4 pH unit had no effect on influx rates for either ion, and we conclude that gill ion uptake systems do not respond rapidly to blood pH changes.

On the interaction of NH+4 and Na+ fluxes in the isolated trout gill.

1. Sodium influx was measured in isolated, previously perfused gill arches of rainbow trout, Salmo gairdneri, by measuring incorporation of 22Na into gill tissue following timed exposure to a 1 mM 22NaCl medium. Transport rates approximated those estimated for intact fish and were linear for at least one min. 2. NH4Cl-containing perfusates at pH 7 and 8 stimulated Na+ influx equally, indicating that only ionized ammonia is important in the transport process. A Na+/NH4+ exchange at basal and/or lateral membranes of the transporting cells is suggested. 3. Low-sodium Ringer perfusate augmented Na+ influx; in one group of gills the transport rate was more than double that of NaCl Ringer controls. The increase in transport induced by internal NH4+ was not additive with the low sodium augmentation. A reduction in intracellular (Na+) is postulated as the mechanism operating in both cases. 4. Ouabain had no appreciable effect on Na+ influx, either with or without NH4+ in the perfusate. Diamox partially blocked the augmented Na+ influx induced by NH4+. Amiloride completely inhibited Na+ influx, both with and without NH4+ in the perfusate.

On the mechanisms of sodium ion transport by the irrigated gills of rainbow trout (Salmo gairdneri).

Sodium uptake by rainbow trout gills has been investigated with a small-volume system enabling rapid, successive flux measurements in different solutions. Sodium influx obeys a Michaelis-Menten type relation, with a K(m) of 0.46 mM, and uptake proceeds unimpaired in the absence of penetrating counter-ions. This suggests a coupled cation exchange. Ammonia output is about the same as the Na(+) influx when external [Na(+)] is 1 mM, but at higher or lower Na(+) influxes, the correlation does not hold. A progressive downward shift in the pH of the irrigating medium as Na(+) influx increases indicates that the exchanging cation is hydrogen. In support of this, acetazolamide, which inhibits Na(+) uptake, also prevents the downward pH shift. The potential across the gill is about 10 mv, body fluids positive, in NaCl solutions up to 10 mM, and is little affected by changes in Na(+) concentration below that. Finally, evidence for locating the rate-limiting step at the outer membrane of the epithelium is presented.