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Distribution, growth, feeding habits, abundance, thermal, and salinity relations of Neomysis mercedis (Holmes) from the Nicomekl and Serpentine Rivers, British Columbia Wilson, Robert Riley

Abstract

A study was made of the distribution, feeding habits, growth, temperature tolerance and salinity relations of Neomysis mercedis. It was found to exist in salt, brackish and fresh water where it feeds on diatoms, algae, vascular plant material, animal material and possibly detritus. Growth to maturity appears to take one year with reproduction occurring in the fall and possibly the spring. There is evidence of two populations, one produced in the fall and the other in the spring. Temperature tolerance was determined by subjecting animals from various acclimation temperatures to a range of temperatures and noting the times to death. The tolerance was determined, in units of square degrees centrigrade, to be 491 units, with the lower and upper lethal temperatures being 0°C. and 23°C. An attempt was made to determine the rate of acclimation to increasing temperature by raising the temperature of separate groups of animals at different rates. Indications were that Neomysis acclimate thermally at a rate faster than 3°C. per day (1°C. per 8 hours). Salinity relations were tested by subjecting animals from a constant salinity to various lower salinities; by gradually reducing the salinity of the environment; by subjecting animals from various salinities to fresh water; and by setting up a salinity or fresh water preference gradient. About 1 o/oo chlorinity was found to be lethal for Neomysis maintained in an environment of 10.33 o/oo chlorinity. Gradually decreasing the salinity over a 6-day period indicated no increased ability by the animals to withstand lower salinities. There is a temporal order in the times to death of animals from various locations up the river (i.e. animals from different salinities) when placed in fresh water with those from regions of highest salinity dying first. In some of the lower reaches of the river surface chlorinity was negligible yet Neomysis taken from these regions existed only for a limited time in fresh water. Those from upper reaches (10—14 miles upstream) survived well in fresh water. The crustaceans exhibited no ability to distinguish fresh from salt water. They did however exhibit a rheotaxic tendency. It is suggested that the rheotaxic response, plus the animal's ability to osmoregulate account for their distribution into fresh water. Indications are that Neomysis mercedis may be suitable for transplantation into some lakes as a supplement to the fish food there.

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