• Brown, Joseph A.
  • Colgan, Patrick W.


We conducted laboratory experiments to determine if juveniles of three species of centrarchid fishes displayed abilities for species or individual recognition. In one experiment we reared rock bass (Ambloplites rupestris) in social isolation and in social groups. Both the isolated and group-reared fish spent significantly more time close to conspecifics than to heterospecifics. These results suggest that species recognition in rock bass is controlled by a closed genetic program and that social experience is not necessary. A second set of experiments was conducted to determine if year-old bluegill (Lepomis macrochirus), pumpkinseed (L. gibbosus), and rock bass juveniles could discriminate between familiar and unfamiliar conspecifics. Bluegill spent significantly more time with familiar conspecifics than with unfamiliar conspecifics, while the other two species displayed no such trend. Bluegill spent significantly more time with familiar conspecifics than did either of the other two species. We postulate that these interspecific differences in recognition abilities may be related to differences in habitat and group parameters among the species.


All experiments were conducted at the Queen's University Biological Station located on Lake Opinicon at Chaffey's Lock, Ontario. The term "fry" indicates fish which have commenced free-swimming and exogenous feeding, and are in the first summer of life. "Juvenile" refers to sexually immature fish older than one year.

In 1980 and 1981, eggs were collected from rock bass, bluegill, and pumpkinseed nests and brought to the laboratory for rearing. During this time we were unable to rear bluegill and pumpkinseed fry in isolation but rock bass fry were found to be relatively easy to rear in isolation from hatching. In 1982 rock bass fry were used in the trials on species recognition. Fish used in the isolation group (IG) were placed individually in 10 L plastic buckets. Twenty buckets with one fry in each were provided with air stones and natural photoperiod. Water was changed twice weekly and two blackchin shiner fry (Notropis heterodon) were placed in each bucket once the rock bass were free-swimming. The shiners were "dither fish" (Barlow 1968) and were used to reduce the appearance of fright behaviour or hyperactivity in the isolated fish. The shiners were chosen because they do not resemble, either morphologically or behaviourally, the stimulus fish with which the IG fry were tested. Fry reared in the social group (SG) were collected from nests (different than the IG) and placed in 90 L aquaria. Four aquaria with 25-40 fry in each were supplied with a continuous flow of lake water and a natural photoperiod. Fry were fed cultured wild plankton or live Artemia sp. nauplii daily.

Following pilot studies (May-September 1980-1981), all tests were conducted in two glass aquaria, 50 x 27 x 30 cm high, divided into three compartments by glass partitions. The compartments were not water tight. The two end compartments were 10 cm long and the central test area was 30 cm. The test area was divided into two grids (15 cm) by vertical black lines drawn on the glass. In each trial a pair of rock bass was placed in one end compartment and a pair of pumpkinseed sunfish (matched for size) was placed in the other. These stimulus fish were trapped from the lake. Pumpkinseeds were chosen because they are sympatric with rock bass in Lake Opinicon, are readily available, and are easy to maintain in the laboratory.