A Comparative Study of the Total Red Counts of Wild and Liver-fed Trout

Abstract

Because of the use of liver as a food for young trout, it was suggested to the writer that a comparative study of the blood of wild and liver-fed trout might show the reaction of normal and growing animals to liver. Although the data are limited, the results indicate an increase in the total red counts of liver-fed trout.

Method. It is well known that fish blood is difficult to work with because it clots quickly, is easily contaminated with mucus, is relatively limited in quantity in small fish, and may change if the fish are out of running water for any length of time. Through the courtesy of the Massachusetts Department of Conservation, Division of Fisheries and Game, blood was obtained from wild trout at the Palmer Hatchery and from liver-fed trout at the Sunderland Hatchery. Haemoglobin determinations were made at the hatcheries but the pipettes for the total counts were brought back to the laboratory. The blood both for haemoglobin determinations and for total counts was taken directly from the ventricle or the sinus venosus into the pipettes.

Total Red Counts. Table I and Fig. 1 give the results of counts made on 11 wild trout and 17 liver-fed trout. Although the lengths of the two kinds of trout are about the same, those which were fed liver possessed much more fat. While 6 of the 11 wild trout have counts less than 2,000,000, all of the 17 liver-fed have total numbers above that value. There appears to be no difference due to sex. The one count of 3,000,000 among the wild trout was obtained from a fish which had been in a bucket of water for one and a half hours before the blood was taken and was consequently very inactive.