Carotenoid pigmentation of chinook salmon (Oncorhynchus tshawytscha)

Abstract

Carotenoid pigmentation of chinook salmon under commercial conditions was investigated in a series of experiments carried out in fresh water and salt water. The carotenoid composition of salmonids and factors regulating the absorption, transport and deposition of these pigments in various salmonid tissues was reviewed.

The influence of dietary lipid on the deposition of astaxanthin by Chinook salmon was investigated. A role for the w3 essential fatty acids in the processes of absorption or deposition was proposed.

Astaxanthin was more efficiently utilised by chinook salmon than canthaxanthin at commercially applicable dietary concentrations. No synergistic effect on carotenoid deposition was observed when fish were fed a 1: 1 mixture of astaxanthin and canthaxanthin. The ratio of astaxanthin to canthaxanthin in the muscle tissues of fish fed a mixture of the two carotenoids ranged from 1:0.71 to 1:9.46 over time indicating the lower utilisation of canthaxanthin relative to astaxanthin.

Decreases in muscle carotenoid concentrations were observed following cessation of dietary carotenoid supplementation of pigmented fish. Continual deposition of carotenoids in the muscle tissue occurred during this period confirming cited literature of carotenoid redistribution from visceral organs.

Colorimetry was identified as a suitable method for the evaluation of salmon flesh colour irrespective of pigment type (astaxanthin or canthaxanthin) or feed regime (supplementation or non-supplementation). Chromaticity was related to carotenoid concentration and measuring site on the fillet. Colorimetric methods for the determination of salmon flesh colour were standardised.

A pale region of muscle tissue, apparently related to maturation, which is observed in the caudal region of some farmed salmon was investigated. No astaxanthin or canthaxanthin metabolites were detected in this region and it was concluded that the pale area was due to the exclusion of astaxanthin or canthaxanthin as opposed to metabolism of thecarotenoids.

Astaxanthin was identified as the predominant carotenoid present in the muscle tissue of wild chinook salmon during the marine phase of their life cycle. M. gregaria has been identified as a source of food for salmonids off the east coast of the South Island, New Zealand (Plane, 1981). High concentrations of astaxanthin were detected as the major carotenoid of these crustacea and it was proposed that seasonal assimilation of M. gregaria is responsible for the intense pigmentation of these fish.