Suppression behavior increased by telencephalic lesions in the teleost, Macropodus opercularis

Previous experiments in several teleost species suggested that defensive reactions are increased following extensive bilateral ablation of the telencephalon. We investigated the effects of varied telencephalic lesions on the reaction of fish to handling and placement in an unfamiliar tank. When intact or sham-operated males were handled, they showed increased rates of surfacing for air. Males which were previously administered bilateral (TLX) or unilateral (UTLX) telencephalon ablation suppressed activity following handling. TLX lesions resulted in the greatest suppression reactions; in addition, the TLX males showed slightly decreased rates of activity prior to handling. Extensive, bilateral lesions of the dorsal telencephalon did not induce the suppression reaction in most males. Based on the results, we propose that one of the functions of the teleost telencephalon is to modulate defensive behavior. The structures which influence defensive behavior appear to be located in the ventral and possibly the rostrodorsal area of the telencephalon.