Philip A. Veillette

Methodology for implanting cortisol in Atlantic salmon and effects of chronically elevated cortisol on osmoregulatory physiology

Abstract A method for achieving high physiological concentrations of cortisol in the plasma of Atlantic salmon (Salmo salar) is outlined. Cortisol was emulsified in vegetable shortening:vegetable oil (1 : 1). This mixture is fluid at 24°C and can be injected into the peritoneum where it solidifies into a slow-releasing cortisol implant. Three doses of cortisol implants were used: 25, 50 and 100 μg/g body weight. Salmon in the post-smolt stage were serially sampled in short-term (1 week) and long-term (1 month) experiments. There was significant variability in the vehicle-implanted control fish over time in both experiments. Except for day of the implant, there were no differences between the implanted controls and the non-implanted controls, indicating that the implant itself was probably not stressful. The medium dose (50 μg/g body weight) was found to elevate plasma cortisol within 1 day and to maintain plasma cortisol above vehicle-implanted salmon for as long as 1 month. The low dose was ineffective after 1 week and the high dose resulted in plasma cortisol concentrations above physiological levels. Exogenous cortisol increased the fluid uptake rate of the non-everted posterior intestinal sac after 1 month and increased the gill Na + K + - ATPase activity after 1 week. These implants might be useful in allowing culturists to move salmon to sea cages at times outside the typical smolt window.

Changes in intestinal fluid transport in Atlantic salmon (Salmo salar L) during parr-smolt transformation.

We examined changes in fluid transport by the intestine of Atlantic salmon (Salmo salar L) undergoing parrsmolt transformation during springtime. In vitro measurements of fluid transport rate (Jv) across non-everted middle and posterior intestinal sac preparations were made in late April and early June 1990 and from February through June 1991 for juvenile smolting fish. Intestinal Jv was also compared between parr- and smolt-stage salmon in both years. To evaluate the osmoregulatory role of the intestine, Jv was measured for smolts adapted to seawater and their cohorts remaining in fresh water. The middle intestine of smolting fish underwent a significant decrease in fluid transport during the springtime, while posterior intestinal Jv significantly increased. Parr-stage fish decreased Jv in the middle intestine during springtime similar to smolts. However, the posterior intestinal Jv of smolts showed a significant increase over the parr around the peak smolt period in both years. Seawater-adapted smolts generally exhibited posterior intestinal Jv approximately double that of freshwater cohorts. A decrease over time shown for the middle intestine, together with the increased Jv in the posterior intestine preceding and after seawater entry, suggests the development of a functional regionalization during parr-smolt transformation, with the posterior intestine taking on increased importance in osmoregulation in seawater.

Cortisol stimulates intestinal fluid uptake in Atlantic salmon (Salmo salar) in the post-smolt stage.

The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na+,K+-ATPase activity, andin vitro measurements of fluid transport rate (Jv) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na+,K+-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na+,K+-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.

Ghrelin in the summer flounder: immunolocalization to the gastric glands and action on plasma cortisol levels.

We searched for evidence of the hormone ghrelin in the stomach of a juvenile, marine teleost, the summer flounder. Using antiserum against the conserved core of the ghrelin peptide, immunoreactivity was observed in the simple, branching epithelium that comprises the gastric glands. The immunoreaction was especially strong in the glandular epithelium located deep in the tissue. Next, we assessed a possible connection between ghrelin and the hypothalamic-pituitary-interrenal axis through a series of three injection experiments in which acylated or non-acylated (des-acyl) ghrelin was injected into the peritoneum of summer flounder (Paralichthys dentatus). A significant increase in plasma cortisol relative to saline-injected controls was observed for the acylated form at a dose of 1000 ng g(-1) of body mass in one of the experiments. In another, there was a trend for des-acyl ghrelin at 1000 ng g(-1) of body mass to increase plasma cortisol. Taken together, this study provides evidence that gastric glands in the stomach of summer flounder are a site of ghrelin production and that peripherally administered ghrelin can stimulate the cortisol axis in a teleost.

Selected hemolymph constituents of captive, biomedically bled, and wild caught adult female American horseshoe crabs (Limulus polyphemus)

Hemolymph from adult female American horseshoe crabs (Limulus polyphemus) was analyzed from wild caught and three treatments from a biomedical bleeding experiment: captive control, captive bled, and handled according to Best Management Practices (BMP). A total of 10 constituents were measured: blood urea nitrogen, creatinine, glucose, lactate, protein, and ionic concentrations of calcium, chloride, magnesium, potassium, and sodium. Protein concentration was positively correlated with size (prosomal width), while sodium and potassium were negatively correlated with size. Only protein concentration differed among groups, with the captive bled BMP group having significantly lower protein values than either captive control or wild crabs. Wild crabs had higher creatinine, glucose, and potassium values compared to all captive groups. Chloride, calcium, magnesium, and sodium concentrations were lower for wild crabs compared to the captive groups. Lower protein values in the captive bled BMP group suggest that prolonged biomedical bleeding may impact crab physiology.