Using scale characteristics and water temperature to reconstruct growth rates of juvenile steelhead Oncorhynchus mykiss.

Juvenile steelhead Oncorhynchus mykiss from a northern California Central Valley population were reared in a controlled laboratory experiment. Significantly different rates of growth were observed among fish reared under two ration treatments and three temperature treatments (8, 14 and 20°C). Wider circulus spacing and faster deposition was associated with faster growth. For the same growth rate, however, circulus spacing was two-fold wider and deposited 36% less frequently in the cold compared to the hot temperature treatment. In a multiple linear regression, median circulus spacing and water temperature accounted for 68% of the variation in observed O. mykiss growth. These results corroborate previous research on scale characteristics and growth, while providing novel evidence that highlights the importance of water temperature in these relationships. Thus, this study establishes the utility of using scale analysis as a relatively non-invasive method for inferring growth in salmonids.

Recovery of warfarin from an enteral nutrient formula.

The in vitro recovery of warfarin from an enteral nutrient formula after filtration to remove the protein-bound fractions was determined. This study was conducted in two parts. In part 1, 0.25-, 0.50-, and 1-mL aliquots of warfarin sodium stock solution were added to 150 mL of the enteral nutrient formula Osmolite under physiologic conditions to produce warfarin concentrations of 16.7, 33.3, and 66.7 micrograms/mL. In part 2, a 0.5-mL aliquot of the warfarin sodium stock solution was added to Osmolite 100 mL-distilled water 50 mL, Osmolite 75 mL-distilled water 75 mL, and Osmolite 150 mL. The samples were filtered through a membrane that retained macromolecules while allowing warfarin to pass through, and the warfarin concentration was measured by high-performance liquid chromatography. Assays of protein-free buffered control solutions of warfarin before and after filtration indicated that no significant amount of warfarin was retained in the filtration membrane. Significantly less warfarin was recovered from full-strength Osmolite after filtering than before filtering at all warfarin concentrations tested. Significantly more warfarin was recovered from the Osmolite-distilled water solutions than from the undiluted Osmolite. These results suggest that there is some sequestering of warfarin in the macromolecular fraction of the enteral nutrient formula. The decreased recovery of warfarin from the enteral nutrient formula used in this study has potential clinical importance, but further research in humans is needed to substantiate these in vitro observations.