LlMNOLOGICAL CONDITIONS AND GROWTH OF TROUT

A small group of lakes near Rotorua has been the sub ject of research by the Marine Department for a number of years to determine the rate of growth of the resident rainbow trout (Salmo gairdnerii) (Smith 1959) and the effect of increasing these trout populations by artificial stocking with hatchery-reared fingerlings. As a result, fish size in some lakes has been noticeably reduced in recent years. It has been shown elsewhere that the quality of the water in a lake has an important effect upon the fish present (Hasler 1947). Some factors affecting water quality were therefore examined during the summer of 1962 in lakes Okataina, Ngapouri and Okaro. These data are correlated with others relating to those trout present which were over 20 em. long (smaller fish are caught nei ther by anglers nor by the gill nets used in research).