How to determine the appropriate mortality in experimental larval rearing? |
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Authors: | Tomonari Kotani Masashi Yokota Hiroshi Fushimi Seiichi Watanabe |
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Institution: | (1) Department of Marine Biotechnology, Faculty of Life Science and Biotechnology, Fukuyama University, 452-10 Innoshima-Ohama, Onomichi Hiroshima, 722-2101, Japan;(2) Department of Marine Biosciences, Faculty of Marine Science, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan;(3) Present address: Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima Kagoshima, 890-0056, Japan |
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Abstract: | Survival in larval rearing experiments is difficult to estimate due to accidental losses and periodic sampling. The number
of sampled fish can be a large proportion of the stocked ones, making it difficult to calculate the overall survival rate
and mortality coefficient as this is based on the initial number. Here, a new method of calculating survival is proposed using
the mortality coefficient. When the initial stocking density and sampled and final numbers are known, and assuming that mortality
coefficient is constant, the final number of fishes can be represented by the formula N
t = e−mt
(N
0 − ΣN
Sne
mdn), where t is rearing period (days), N
0 indicates initial number, N
t indicates the survival number at t days of rearing, m is the natural mortality coefficient, N
Sn is the sampled number in the nth sampling, and dn is the rearing period until removal of the nth sample. The provisional mortality coefficient is calculated from initial and final stocking numbers. Then values for the
natural mortality coefficient are substituted into the formula with successive approximation. The coefficient, which most
closely approximates the actual survival, is determined as the best fit natural mortality coefficient. Examples of larval
experiments are provided to demonstrate the method and show that survival is often underestimated using traditional methods. |
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Keywords: | |
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