Abstract
Background:
The cutbow trout (Oncorhynchus mykiss x clarkii) is a fertile hybrid of rainbow and cutthroat trout. Little published length-weight data is available for this hybrid, and a standard weight curve is not established. Eleven Mile Reservoir is a clear mountain reservior in Colorado with a surface area of 13.4 square kilometers, an average depth of 10 m, and a maximum depth of 41 m. 80,000 cutbow trout were stocked through the ice in late winter before samples were taken.
Materials and Methods:
Angling provided 171 samples which were weighed and measured (total length and fork length). Dressed weight was also determined with the scales, head, and entrails removed. Estimates of parameters a and b in the model, W(L) = aLb, were obtained by both linear least-squares (LLS) regression (log(W) = log(a) + b log(L)) and non-linear least-squares (NLLS) regression, where W is weight in kg and L is length in cm. Parameter estimates of an improved model, W(L) = (L/L1)b, were also determined by NLLS regression; the parameter L1 is the typical length of a fish weighing 1 kg. The resulting best-fit parameters, parameter standard errors, and covariances are compared between the two models. Average weight and length are considered for each month from June through October to estimate growth rates for fish stocked over the winter. Standard weights (relative to the rainbow trout and cutthroat trout standard weight curves) are also determined, along with the ratio of total length to fork length and typical dressed weight percentage.
Results:
The improved model parameter estimates were b = 2.662 and L1 = 45.32 cm, with correlation coefficient r = 0.969. From June to October, mean relative weight decreased from 101.5% to 93.6% relative to the rainbow trout standard weight and 114.5% to 103.2% relative to the cutthroat trout standard weight as mean total lengths increased from 34.4 cm to 41.9 cm and the mean weights increased from 0.505 kg to 0.830 kg. Typical dressed weight is 71% of the total weight.Conclusion: Eleven mile reservoir is an excellent trout fishery, capable of producing large numbers of cutbow trout in good condition. The cutbow trout is well suited to this kind of mountain reservoir and grows fast. As might be expected, the weights of cutbow trout of a given length tend to fall between the standard weights of the rainbow and the cutthroat. For the season, the average relative weight was 97.0% relative to the rainbow trout, and 108.3% relative to cutthroat trout.
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Parker, D., Avers, T. & Courtney, M. Weight, Length, and Growth in Cutbow Trout (Oncorhynchus mykiss x clarkii). Nat Prec (2011). https://doi.org/10.1038/npre.2011.6432.1
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DOI: https://doi.org/10.1038/npre.2011.6432.1