The total lipid and fatty acid content of Spirulina platensis UTEX 1928 was 7.2 and 2.2% respectively of cellular dry weight under controlled conditions supporting high growth rates. With increases in irradiance from 170 to 870 umol photon m-2 s -', growth rate increased, total lipid decreased, and fatty acid composition was unaffected. At 1411 #mol photon m -2 s -1, total lipid increased slightly and percent composition of the fatty acid gamma linolenic acid increased.Growth and total lipid content of S. platensis were affected by changes in growth temperature from 25 to 38 °C. With increased growth rate, total lipid content increased. This suggests that the storage of carbon increases at temperatures supporting high growth rates. The degree of saturation increased with temperature. Although the percent composition of gamma linolenic acid was higher at lower growth temperature, production was still primarily a function of growth rate. The effect of temperature on fatty acid content and degree of saturation was of secondary importance.Nitrogen starvation increased total lipid content but decreased fatty acid content as a percentage of dry weight; composition of the fatty acids was unaffected. N-starvation appeared to suspend synthesis of long chain fatty acids in S. platensis, suggesting that some other compound stores fixed carbon when nitrogen is limiting.It was concluded that fatty acid production in S. platensis is maximized by optimizing culture conditions for growth.

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The quantitative and qualitative effects of light on carotenoid production by Spirulina were studied. Maximum total carotenoid production was measured in cells grown under white light at an irradiance of 432 pmol photon m-2 s -, the onset of light saturation for this organism as determined by growth rates. A true maximum may exist at irradiances above 1500 mol photon m -2 s-t under white light.Individual carotenoids responded differently to light conditions. Under white light, fB-carotene and echinenone were most abundant at the lowest and highest irradiance levels tested. Myxoxanthophyll and lutein/zeaxanthin did not change over the same irradiance range. Under red and blue light, we found decreased values of myxoxanthophyll, while fl-carotene increased and lutein/zeaxanthin and echinenone showed little change. In general, maximum carotenoid production requires optimization of the culture conditions that favor growth.

One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production.Our results suggest that through additions of CO 2 gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO 2 increased levels of dissolved CO 2 , total dissolved inorganic carbon (CO 2 ), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM YCO 2 was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO 2 .

Cholesterol is considered a required nutrient for penaeid shrimps, but an optimal level has not been defined. A 68-day grow-out trial was conducted in 1300-L outdoor tanks in Hawaii, USA, to determine the cholesterol level required in a soyabean meal-based diet for juvenile Pacific white shrimp, Penaeus vannamei (Boone).Test feeds were prepared by adding six cholesterol levels (1.0-10.2 g kg-', as-fed basis) to a standard diet high in plantprotein meals, starch and flour. These feeds were provided to the shrimp three times daily.Harvest weights and weekly growth increments varied significantly among diets. The 2.3 g kg-' and 4.2 g kg-' cholesterol diets yielded better growth than the 1.0 g kg-' and 10.2 g kg-' diets. Survival and feed conversion ratios did not vary significantly among diets.Significant dietary cholesterol effects on growth of P. vannamei in conditions resembling commercial grow-out indicate that its inclusion in practical diets at more accurately defined levels is necessary. Optimal cholesterol levels for juvenile shrimp may be lower than those now utilized, and may vary relative to the contribution of free sterols from natural foods in shrimp ponds.

Pond water quality and associated microbial biomass were studied in relation to the type of feed applied during the culture of the marine shrimp Penaeus vannamei. The feeds tested included conventional feedlot manure as well as two feeds based on bagasse, a sugarcane waste product.Physical and chemical parameters were studied during a 100 day trial in 200 m2 earthen ponds.Both bagasse-based feeds supported a significantly larger microbial community as measured by specific biomass numbers (P < 0.01), ATP content (P < 0.001) and amount of the particulate organic matter present on pond bottoms (P -= 0.025). For both bagasse-based treatments, the estimated bacterial cell number in the flocculent layer was 3.11 x 1012/m2, compared to the much lower cell number of 7.53 x 1010/m2 for control ponds. Harvest data suggest that bagasse forms a potential base for feeds when applied to extensive shrimp cultures.

One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production.Our results suggest that through additions of CO 2 gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO 2 increased levels of dissolved CO 2 , total dissolved inorganic carbon (CO 2 ), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM YCO 2 was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO 2 .

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