Visual pigment changes in juvenile kokanee salmon in response to thyroid hormones

Tetraiodothyronine ( T 4 ) or triiodothyronine ( T 3 ) injected intraperitioneally into juvenile kokanee (landlocked sockeye salmon), Oncorhynchus nerka , results in a marked increase in the percentage of the retinene 2 based visual pigment when compared to sham injected controls. Controls have predominately retinine 1 based visual pigment. Doses of 100 μg of T 4 cause nearly a complete conversion from retinene 1 to retinene 2 visual pigment i.e. from VP503 1 to VP527 2 . These results are contrary to what has been reported when thyroid hormone is injected into bullfrog tadpoles. Tadpoles have shown an increase in the amount of vitamin A 1 and presumably of the retinene 1 visual pigment when injected with thyroid hormone. The possible implications of the results are discussed in relation to visual pigment conversions that occur in a number of paired pigment species.