• Keast, Allen


Young fish of six species in an open water community all began their exogenous feeding by taking nauplii and small cyclopoids of body length (less tail) of 0.1–0.3 mm. Appearance of larvae of the different species in the system was, however, sequential, the resource being utilized by the different species in turn. The sequence was: Perca flavescens, Percina caprodes, Pomoxis nigromaculatus, Ambloplites rupestris, Lepomisgibbosus and L. macrochirus.

The larvae and juveniles changes their diet rapidly as they grew. Fish 10–14 days after hatching and 8–10 mm in length i.e. close to the beginning of the juvenile period, consumed larger-bodied prey items (including several genera of Cladocera) and had more diversified diets than the 4.5–6.0 mm first-feeding larvae. These differences, and progressive dispersal of the larger young from the area, served to minimize the chances of food competition between batches of young of different ages.

The composition of the fish community of larvae changed from week to week as new species entered it, increased in size and departed. Patterns of food utilization changed accordingly.

Numbers of cyclopoids, their nauplii, and Bosmina longirostris, fell rapidly in May — early June, and did not increase again until August. These changes coincided with the rise and fall in numbers of the young fish in the habitat.


The study lake Lake Opinicon is a small eutrophic lake of 3.7 x 0.6 km and maximum depth of 10 m in the Rideau Canal System. Its physiography and temperature regime is typical of many small lakes in eastern Ontario. It is ice-covered from December to mid-April and the spawning of the dominant perciform fishes extends from early May to late July. Netting and processing procedures

Netting of the young fish was by twin conical nets of mesh size 0.5 mm with a mouth diameter of 61 cm mounted at the ends of a 3 m long wooden frame placed across the bow of the boat (see Amundred et al. 1974). The nets were 2.5 m long and tapered to a diameter of 10 cm, terminating in a 2 liter plankton bucket. The tows were made in water 1.442.3 m deep, parallel to the shore with the boat moving at the speed of 38.5 m per minute.