Dave A. Higgs

Potential for dietary phytase to improve the nutritive value of canola protein concentrate and decrease phosphorus output in rainbow trout (Oncorhynchus mykiss) held in 11°C fresh water

This study assessed the potential for using dietary phytase to improve the nutritive value of canola protein concentrate (CPC) for rainbow trout, and to concomitantly minimize phosphorus discharge into the environment. Eight diets were prepared. LT-anchovy meal (AM) provided 89% of the protein in the basal diet, whereas in the remaining diets, 59% of the protein originated from CPC by replacement of AM protein. Four CPC diets were supplemented with phytase (Natuphos®) at levels of either 0, 500, 1500 or 4500 phytase units (FTU)/kg diet together with 4505 mg/kg phosphorus. Two CPC diets contained 1500 FTU/kg and either 0 or 2253 mg/kg of supplemental phosphorus. The seventh CPC diet contained no phytase or supplemental phosphorus. A commercial trout feed served as an industry control. All diets were fed to triplicate groups of rainbow trout (initial weight, 17.9 g) to satiation daily for 84 days. Mean water temperature was 11.0°C. The level of phytic acid degradation and the apparent availability of dietary phosphorus were ascertained for all groups. Fish fed the CPC diets, regardless of their phytase and phosphorus levels, exhibited growth rates, feed efficiencies and protein utilization comparable to those of control fish. There was, however, a clear positive dose-response of phytase on dietary phytate digestibility and phosphorus availability was improved significantly by the highest level of phytase. We conclude that dietary phytase has potential to improve the nutritive quality of CPC for rainbow trout and the availability of phytate phosphorus.

Influence of dietary amino acid composition on thyroid function of juvenile rainbow trout, Oncorhynchus mykiss

Abstract The acute (3 days) and chronic (21 days) effects of dietary protein quality on thyroid function and growth parameters were studied in immature rainbow trout held at 12°C on a LD 12:12 light cycle. Five isocaloric (∼17.2 MJ digestible energy/kg dry diet) and isonitrogenous (45.1% protein) diets varying in amino acid composition were fed by hand once daily. The ration across all groups was consistent and varied between 1.0 and 1.5% of wet body wt. The dietary amino acid profiles mimicked that within the rainbow trout egg protein (EP), or whole-body protein (WBP), or they were varied widely by altering the proportions of casein and gelatin, i.e. HC/LG (high casein/low gelatin); MC/MG (medium casein/medium gelatin); LC/HG (low casein/high gelatin). Since these diets contained a chemo-attractant (FinnStim) to enhance food intake, a sixth diet, EP/NF (EP but lacking FinnStim), was used to ascertain FinnStim effects. Thyroid function was assessed from plasma levels of T 4 (L-thyroxine) and T 3 (3,5,3′-triiodo-L-thyronine), and from the activity of the hepatic microsomal T 4 5′-monodeiodinase (5′D) which converts T 4 to the more active T 3 form. After 3 days, plasma T 3 and T 4 titres were unaffected by diet, but 5′D activity was depressed by FinnStim and lowered in fish fed diets WBP and LC/HG relative to those fed diet MC/MG. After 21 days, plasma T 3 was uninfluenced by diet, but plasma T 4 was elevated in trout ingesting diet MC/MG. The 5′D activity was lower in fish fed diet WBP than in those receiving diets MC/MG and LC/HG. Final body weight was greater for fish fed diet EP/NF than for those fed diet LC/HG. Fork length was uninfluenced by diet, but the condition factor was depressed in fish fed diet LC/HG. Feed efficiency and percent protein deposited were depressed, whereas hepatosomatic index was elevated in fish fed diet LC/HG. It is concluded that thyroidal status, as judged primarily by hepatic 5′D activity, is influenced in trout both acutely and chronically by the profile of dietary amino acids. The diet high in gelatin content exerted the most consistent effects by depressing growth, condition factor, feed efficiency, and protein conversion into body protein, while simultaneously increasing both the mass of the liver and its 5′D specific activity. Further study is required to identify the particular amino acid(s) responsible for increasing hepatic 5′D potential under conditions of reduced growth.

Residues of PBDEs in northeastern Pacific marine fish: Evidence for spatial and temporal trends

In the flesh (skinless fillet) of chinook, chum, coho, pink, and sockeye salmon (Oncorhynchus tshawytscha, O. keta, O. kisutch, O. gorbuscha, and O. nerka, respectively), sablefish (Anoplopoma fimbria) and walleye pollock (Theragra chalcogramma) from several sites in the northeast Pacific sampled between 2002 and 2008, tetra- and pentabrominated diphenyl ethers (BDEs) (BDE 47, 49, 99, and 100) dominated the congener distribution. Chinook and sablefish contained the highest concentrations, followed by sockeye, coho, and pink salmon, and pollock. In sockeye from the Bering Sea - Aleutians and from the Gulf of Alaska, total tri- to hepta-BDE concentrations fell significantly between 2002 and 2005; in sablefish from Gulf of Alaska, there was a steady but statistically nonsignificant decline in BDE concentrations between 2002 and 2008. Relative proportions of the main BDE congeners did not change appreciably over time, within species or location. All species except sockeye salmon showed a clear southeastward increase in BDE concentrations, implying an increasing gradient in general ecosystem contamination. In chinook, coho, and sablefish, especially, the southeastward trend in increasing total concentrations was associated with increasing proportions of BDEs 47 and 100. Chinook returning to western North American natal streams appeared to accumulate most of their PBDE burden towards the end of their migration. Fish from more northern sampling sites often had higher proportions of more highly brominated congeners than those from more southern sites, perhaps reflecting contamination from Asian sources where higher-brominated commercial PBDE formulations are used. In sablefish and pollock, the relative proportions of BDEs 99 and 47 varied inversely in almost a 1:1 ratio, implying debromination of BDE 99 to 47.