Learning in fish with transplanted brain tissue.

Material taken from fish embryos during gastrulation was implanted at prospective tectal sites in host embryos of the same age and species. When mature, the hosts were trained in a series of habit reversals. Two of six animals showed progressive improvement in reversal (a phenomenon not typically found in fish, but characteristic of higher animals), two showed unusually few errors, and two behaved normally. Differences in performance were correlated with differences brain structure.