We report the results of controlled feeding trials on the tiger shrimp, Penaeus monodon (Fabricius). The desired colour was obtained by feeding a diet supplemented with astaxanthin (50 p.p.m) for 7± 8 weeks before harvest. Similar coloration was achieved, however, by including in the feed an algal material (Dunaliella salina) that contains bcarotene but no astaxanthin. Feed containing bcarotene at 125 p.p.m also gave the required coloration at 7±8 weeks, whereas the same results was obtained after only 5±6 weeks when feed containing 175 p.p.m b-carotene was used. Irrespective of whether the shrimp were fed astaxanthin or b-carotene, the main carotenoid accumulation was astaxanthin, in free and esteri®ed form, showing that P. monodon has the metabolic ability to convert b-carotene into astaxanthin. The supplementation with b-carotene or astaxanthin had no signi®cant effect on growth, average ®nal weight, survival rate or feed conversion ratio, nor on the immune response of the shrimp in terms of production of haemocytes phenoloxidase in the cytoplasmic granules of the haemocytes, microbial clearance ability and resistance to infectious diseases. This is a highly signi®cant development for commercial aquaculture, because it shows that supplementing diets with b-carotene can achieve the same result as doing so with much more expensive astaxanthin.
A method is described for saving 30% of the world fish catch by producing fishmeal and fish oil replacement products from marine microalgae, the natural source of proteins and oils in the marine food web. To examine the commercial aspects of such a method, we adapt a model based on results of microalgae production in Hawaii and apply it to Thailand, the world’s fourth largest producer of fishmeal. A model facility of 111 ha would produce 2,750 tonnes yr−1 of protein and 2,330 tonnes yr−1 of algal oil, at a capital cost of $29.3 M. Such a facility would generate $5.5 M in average annual net income over its 30-year lifetime. Deployment of 100 such facilities in Thailand would replace all domestic production of fishmeal, 10% of world production, on ~1.5% of the land now used to cultivate oil palm. Such a global industry would generate ~$6.5 billion in annual net income.
A feeding experiment was conducted to characterize essential fatty acid deficiency and to de termine the effect of dietary n-6 and n-3 fatty acids on growth and histological changes of white fish Coregonus lavaretus maraena. Growth, feed efficiency together with survival rate were lowest in fish fed a diet containing 5% 18: 1n-9 as a sole lipid source. On the otherhand, all parameters were effectively improved by supplementation with n-3 fatty acids, and were highest in fish receiving the diet containing n-3 highly unsaturated fatty acids (HUFA) greater than 0.5%. However, 18: 2n-6 was found to be ineffective for enhancing growth. Addition of 18: 2n-6 to 18: 3n-3 did not further improve growth and feed efficiency. The fish fed the 18: ln-9 diet showed swollen pale livers with abnormalities in histological analysis. This abnormal histological condition was improved by supplementation of 0.5% n-3 HUFA. The ratio of 20: 3n-9 to 22: 6n-3 in the fatty acid com position of polar lipid fractions from the livers, one of the EFA indices for freshwater fish, was highest in the EFA-deficient group and lowest in the fish receiving 1% n-3 HUFA in diet.These results indicate that n-3 fatty acids are essential for white fish.
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