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The effect of changing feeds on individual feed intake and feeding and dominance ranks in groups of African catfishClarias gariepinuswas investigated. Following feeding on a commercial feed groups( n = 3) of six African catfish were either fed fish meal(FM42) or maize gluten(MG35) based feeds for 5 days before being switched to the other feed for 5 days. Energy intake was significantly lower on FM42 than on MG35, dry matter intake and protein intake were significantly lower on FM42 than on commercial feed and this occurred whether FM42 was fed first or second. There were no significant differences between intake of MG35 and commercial feed. Thus, the action of changing the feed on its own did not affect feed intake since the decrease was shown to be feed-specific to FM42. Six types of agonistic behaviours were identified and used to assign dominance rank. There were no correlations between dominance and feeding ranks. This was due to non-linear hierarchies with one dominant fish in each group. Feeding ranks were more stable when feeding MG35 than FM42. Feeding rank stability(Kendall's coefficient of concordance) was significant in five out of six groups fed MG35(compared with three out of six fed FM42). Feeding rank stability was higher in five out of the six groups when they were fed MG35 than when the same group was fed FM42. The experiment provided evidence that the introduction of a novel feed can, but does not necessarily, alter feed intake and that feed can influence the stability of feeding ranks. [ABSTRACT FROM AUTHOR]

Abstract Gastrointestinal and serum absorption of astaxanthin was studied in rainbow trout, Oncorhynchus mykiss (Walbaum) (217 ± 2 g) fed diets supplemented with either esterified astaxanthin (from Haematococcus pluvialis) or free astaxanthin (synthetic, as 8% w/w beadlets) at similar levels (50 mg kg[sup -1]). After 56 days of feeding, there was a significant difference (P = 0.0582) between steady-state serum astaxanthin concentrations for fish fed free (2.0 ± 0.3 μg mL[sup -1]) or esterified astaxanthin (1.3 ± 0.1 μg mL[sup -1]) at the 90% confidence level. However, following ingestion of a single meal supplemented with free or esterified astaxanthin, the rates of astaxanthin absorption into serum were not significantly different (P > 0.1) (0.8 ± 0.2 µg mL[sup -1] h[sup -1] and 1.0 ± 0.4 µg mL[sup -1] h[sup -1] respectively). In fish fed both free or esterified astaxanthin, higher absorption (P < 0.05) of astaxanthin by the ileal (0.8 ± 0.14 μg g[sup -1] and 0.9 ± 0.15 μg g[sup -1] respectively) compared with the posterior (0.2 ± 0.01 μg g[sup -1] and 0.3 ± 0.14 μg g[sup -1] respectively) intestine was recorded. This confirmed the role of the anterior intestine in carotenoid absorption. Non-detectable levels of esters in digesta taken from the hind intestine suggest the anterior intestine is also the primary region for ester hydrolysis. [ABSTRACT FROM AUTHOR]

The deposition of natural, optically active, astaxanthin fatty acid esters in rainbow trout (Oncorhynchus mykiss ) was studied. Mono-esterified and di-esterified (3S ,3′S ) astaxanthin were purified from the green microalga Haematococcus pluvialis and incorporated into extruded diets and compared with diets containing synthetic racemic astaxanthin (Carophyll Pink) and a total carotenoid extract from the alga. All sources of astaxanthin achieved >4 mg kg-1 in the white muscle after 6 weeks feeding. No significant difference (P > 0.05) between the deposition of astaxanthin or total carotenoid for the different diets was observed. Other xanthophylls, namely lutein, zeaxanthin and idoxanthin were found in the white muscle of rainbow trout fed all diets and together accounted for 10–14% of total carotenoid. Astaxanthin was deposited in the white muscle in the stereochemical form administered in the diet, i.e. racemic astaxanthin for Carophyll Pink and 100% (3S ,3′S )-astaxanthin for the algal sources. In contrast, epimerization of (3S ,3′S ) astaxanthin from the alga was observed for the astaxanthin esters deposited in the skin of rainbow trout, with a ratio close to 1.0:2.0:1.0 (3S ,3′S:3R ,3′S:3R ,3′R ). [ABSTRACT FROM AUTHOR]