Interactive effects of high stocking density and triiodothyronine‐administration on aspects of the in vivo intermediary metabolism and in vitro hepatic response to catecholamine and pancreatic hormone stimulation in brook charr, Salvelinus fontinalis

Abstract

Brook charr (Salvelinus fontinalis) were maintained at one of two stocking densities (SD) (30 or 120 kg/m3) and fed either a control or a T3-supplemented (20 mg/kg) diet for 30 days in order to investigate possible interactive effects of SD and T3-administration on growth, feeding rate, food conversion efficiency, and hepatic and dark muscle enzyme activity. In addition, liver slices were incubated in vitro for 6 h with epinephrine, norepinephrine, isoproterenol, propranolol, insulin, glucagon, or somatostatin to evaluate possible SD-T3 interactive effects on hepatic responses to hormonal stimulation. Maintaining the fish at high SD appeared to increase the clearance rate of T3 from the T3-supplemented group. There was no clear evidence of SD-T3 interactive effects on growth rate, feeding rate, or food conversion efficiency, although T3-administration decreased food conversion efficiency, and high SD decreased growth and feeding rates. Of the hepatic enzymes studied, HOAD, malic enzyme, G6PDH, CS, PFK, HK, and GDH activities all showed changes suggestive of interactive SD-T3 effects. Although hepatic FBPase was stimulated by both high SD and T3-administration, there was no evidence of interactive SD-T3 effects. Dark muscle HOAD, CS, and PFK also showed SD-T3-related responses; dark muscle malic enzyme, G6PDH, HK, and GDH were unaffected by either altered SD or T3-administration. Prior treatment of the fish with T3 and high SD had significant effects on free fatty acid (ffa) release to the medium and on hepatic lipid content, but had no effect on the responses to the various endocrine agents used. Glucose release from liver slices of fish stocked at high density (both T3-supplemented and controls) was higher than that of the fish stocked at low density; with the exception of insulin and glucagon, glucose release was similar in all pre-treatment groups. The insulin- and glucagon-stimulated changes in glucose release seen in the fish fed non-supplemented diets were not found in the two groups of fish fed the T3-supplemented diets. High SD and/or T3-administration induced significant lowering of hepatic glycogen content, but there was no effect of pre-treatment on the response to any of the endocrine agents used. The data show a marked effect of SD on energy partitioning processes in brook charr and the animal's ability to respond to T3-stimulation, but provided no evidence of such effects on the liver response to the various agents used.

Effect of stocking density on growth and serum concentrations of thyroid hormones and cortisol in Amur sturgeon, Acipenser schrenckii

“…Several studies have found the densityrelated alterations in pituitary-thyroid axis when investigating the influences of stocking density on fish behavior, development, and growth (Leatherland and Cho 1985;Schreck and Patino 1985;Vijayan and Leatherland 1988;Scott-Thomas et al 1992). At high stocking density, decreases in both growth rate and plasma T 4 level were observed both in rainbow trout (Oncorhynchus mykiss) (Leatherland and Cho 1985) and in brook charr (Vijayan and Leatherland 1988).…”

Physiological responses of juvenile wedge soleDicologoglossa cuneata(Moreau) to high stocking density

“…Stocking density did increase plasma cortisol levels and this coincided, indeed, with hyperglycaemia and decreased liver glycogen content in the wedge sole. Cortisol‐induced changes in hepatic glycogenolitic potential, gluconeogenic capacity and glucose export capacity may be the basis of this observation (Vijayan, Ballantyne & Leatherland 1990; Scott‐Thomas, Ballantyne & Leatherland 1992; Vijayan, Pereira, Grau & Iwama 1997; Laiz‐Carrión, Sangiao‐Alvarellos, Guzmán, Martín del Rio, Míguez, Soengas & Mancera 2002; Trenzado, Carrick & Pottinger 2003; Laiz‐Carrión, Guzmán‐Jiménez, Martín del Río & Mancera 2005; Sangiao‐Alvarellos, Guzmán, Laíz‐Carrión, Míguez, Martín del Río, Mancera & Soengas 2005). However, plasma glucose values did not increase in fish kept at the highest density.…”

Correlation between dietary lipid:protein ratios and plasma growth and thyroid hormone levels in juvenile Arctic charr, Salvelinus alpinus (Linnaeus)

“…Plasma T 4 and T 3 concentrations were measured using the Amerlex solid phase radioimmunoassay kits (Johnson & Johnson Clinical Diagnostics, Markham, ON, USA) previously described and validated for use with various salmonid species, including brook charr, Salvelinus fontinalis (Linnaeus) (Scott‐Thomas, Ballantyne & Leatherland 1992). For the thyroid hormones, microradioimmunoassays requiring 5–20 μL of plasma were employed, as developed and described previously (Leatherland, Hilliard, Macey & Potter 1990).…”