Two separate experiments were conducted to investigate the effects of canthaxanthin dose and level of dietary fat on apparent digestibility of canthaxanthin in rainbow trout (Oncorhynchus mykiss). The effect of dose on apparent digestibility of canthaxanthin was determined by feeding a semi-puri-fied diet containing five levels of canthaxanthin (15, 30, 60, 120, and 240 mg/kg DW), and the effect of dietary lipid level on apparent digestibility of canthaxanthin was determined by varying the lipid level in five diets from 4.1 to 23.0%. Apparent digestibility of canthaxanthin was determined using Cr2O3 as an indicator and the faecal extrusion method for sample collection. Increased dietary levels of canthaxanthin decreased apparent digestibility while increased dietary lipid levels increased apparent digestibility of canthaxanthin. The experiments also showed a large, progressive, systematic error caused by the faecal extrusion method over the 3-day sample collection period. The results are discussed in relation to available literature on carotenoid absorption and deposition.

The apparent digestibility and utilization of fish protein subjected to the ensilaging process were compared with fish meal in dry diets fed to rainbow trout (Salmo gairdneri). During the ensilaging process, a majority of the proteins were converted to peptides, a portion of which was further hydrolyzed to free amino acids. Although apparent digestibility values were higher for the fish silages than for fish meal, the fish silages were not as efficiently utilized for growth. Whole fish and fish processing wastes were found to be equivalent sources of nitrogen provided the degree of autolysis was the same and the diets were otherwise nutritionally balanced. Autolysis was reduced and growth rates enhanced when the ingredients were stored at −5°C prior to ensiling.

AbstractFish silage, canola meal, and wheat bran were blended to form an acid‐stabilised, paste‐like product. Changes in protein nitrogen, non‐protein nitrogen, phytic acid, and orthophosphorus contents of the acidified blends were measured over a 5‐week period of storage at room temperature (20–22°C). During the storage period, phytic acid from the canola meal was dephosphorylated by phytase from the wheat bran. Changes in the level of non‐protein nitrogen showed that the fish proteins were partially hydrolysed and liquefied during storage, and that the fish enzymes may have partially hydrolysed the canola meal and wheat bran proteins. The resulting product could be stored at room temperature without spoiling and could be dried in conventional drying equipment. This process provides a means of improving the nutritional value of canola meal by reducing its high phytate content, and of producing a homogeneous dry feed commodity from liquid fish silage.