Absorbance of retinal oil droplets of the budgerigar : sex, spatial and plumage morph-related variation

Intraspecific variation in photoreceptor physiology is known in several vertebrate taxa, but is currently unknown in birds, despite many avian traits varying intraspecifically, and avian visual ecology encompassing a wide range of environments and visual stimuli, which might influence spectral sensitivity. Avian retinal photoreceptors contain light absorbing carotenoid-rich oil droplets that affect vision. Carotenoids are also important plumage components. However, our understanding of the regulation of carotenoids in oil droplets remains rudimentary. Among birds, Melopsittacus undulatus has probably the best-studied colour vision, shows profound intraspecific variation in plumage colour, and increased plasma carotenoids during moult. We used microspectrophotometry to determine whether a relationship exists between oil droplet carotenoid concentration and plumage pigmentation, and tested for sex and spatial variation in droplet absorbance across the retina. Absorbance of one variety of P-type droplets was higher in males. No relationship was found between droplet absorbance and plumage colour. We found a spatial pattern of droplets absorbance across the retina that matched a pattern found in another parrot, and other avian species. Our work provides insights into the development and maintenance of retinal oil droplets and suggests a common mechanism and function for carotenoid deposition in the retina across bird species.

Effects of Dietary Vitamin B6 Supplementation on Fillet Fatty Acid Composition and Fatty Acid Metabolism of Rainbow Trout Fed Vegetable Oil Based Diets

Fish oil replacement in aquaculture feeds results in major modifications to the fatty acid makeup of cultured fish. Therefore, in vivo fatty acid biosynthesis has been a topic of considerable research interest. Evidence suggests that pyridoxine (vitamin B₆) plays a role in fatty acid metabolism, and in particular, the biosynthesis of LC-PUFA has been demonstrated in mammals. However, there is little information on the effects of dietary pyridoxine availability in fish fed diets lacking LC-PUFA. This study demonstrates a relationship between dietary pyridoxine supplementation and fatty acid metabolism in rainbow trout. In particular, the dietary pyridoxine level was shown to modulate and positively stimulate the activity of the fatty acid elongase and Δ-6 and Δ-5 desaturase enzymes, deduced by the whole-body fatty acid balance method. This activity was insufficient to compensate for a diet lacking in LC-PUFA but does highlight potential strategies to maximize this activity in cultured fish, especially when fish oil is replaced with vegetable oils.