Two marine algal products MAP3 and MAP8 were examined for their suitability as fishmeal protein substitutes in feeds of three prominent farmed species, through shortterm feeding studies. Algal meals were tested at 5 and 10% protein replacement levels for Atlantic salmon and at 25 and 40% for common carp and whiteleg shrimp. At the end of the 12-week period, the growth and feed performance of the two fish species did not reveal any significant difference between those fish offered the algae-based feed and those offered the control feed. The whole body proximate compositions of Atlantic salmon fed the control and algae-based feeds were not significantly different. In common carp, the lipid content in the fish fed higher level of MAP3 was significantly lower than that of the fish fed the control feed. In whiteleg shrimp, at the end of the 9-week feeding period, growth performance and feed utilization did not differ between the treatment groups. Protein content in the shrimp fed the higher level of MAP8 was significantly lower than that of shrimp on the control feed. The three species could accept the algal meals in their feeds at the tested levels, though there were some noticeable effects on body composition at higher inclusion levels.

The aqueous extracts of four marine algae, Caulerpa racemosa var. macrophysa, Gracilaria tenuistipitata var. tenuistipitata, Sargassum sp., and Ulva lactuca, from the coastal areas in Southern Thailand, were prepared by boiling dried seaweed powder in water for 3 h, and by autoclaving each sample at 120 degrees C for 3 h. They were then freeze-dried and evaluated for their antioxidant activities using DPPH (1, 1-diphenyl-2-picrylhydrazyl), hydroxyl radical (OH(*)) and superoxide anion (O(2)(*-) ) scavenging assays. Boiling extracts of the seaweeds, except C. racemosa, were found to have higher total phenolic contents (TPC) than those obtained from the autoclave method. The antioxidant results also showed that O(2)(*-) scavenging activity existed only in the boiling extracts of C. racemosa, G. tenuistipitata, and U. lactuca. In DPPH and OH(*) assays, however, almost all the boiling extracts were less active than the autoclave ones. Among the four alga species, Sargassum sp. was the most active. Both extracts of this seaweed had the highest TPC and also displayed the strongest DPPH(*) and OH(*) inhibitory activities. A strong positive-correlation between the antioxidant potency and TPC of the autoclave extracts was found, while for the boiling extracts such relation was very weak. This result thus reflected that in addition to the phenolic compounds, there might be some other active components present in these extracts involved in the antioxidant activity.

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.

Pre-soaking of the feed pellets in water can improve feed utilization in juvenile green turtles (Chelonia mydas Linnaeus, 1758), but the pre-soaking has not previously been optimized. This study aimed to optimize the water amount used for pre-soaking the pellets. The experiments followed a completely randomized design with three replications of each dietary treatment group. Initially 10-day-old green turtles (20-22 g body weight) were treated in an indoor aquaculture system for 3 months. The dietary treatment pellets were pre-soaked with 0.3, 0.5 or 0.7 (v/w) relative amounts of water that are here termed soaking ratios. At the end of experiment, there were no significant differences in survival (96% on average) and growth (average body weight 75.34 g and specific growth rate 2%/day, on average) of turtles in three dietary treatments (p > 0.05). Feed utilization was the best in turtles fed with 0.7 pre-soaked ratio, as indicated by significant reductions (p < 0.05) in the feeding rate (7.44% body weight/day) and the feed conversion ratio (1.12 g feed/g gain). Digestion was also improved by the induction of faecal digestive enzymes as well as the faecal thermal properties. The rapid growth did not negatively affect the general haematological parameters of reared turtles. These findings indicate that the pre-soaking of feed pellets at the optimal soaking ratio (1:0.7 w/v of pellet to water) can contribute through improved feed utilization of green turtles.

The effects of the hot water extract from Sargassum sp. on the growth performance, immune responses, oxidative stress, and resistance of Asian sea bass (Lates calcarifer) to Streptococcus iniae were investigated. Four groups of fish were fed on the basal diet containing the extract at 0, 0.5, 1.0, and 2.0 g kg −1 diet for 30 days. Thereafter, the fish from each group were divided into equal halves. The first half was injected intraperitoneally with 0.85 % NaCl, and the second half was injected with S. iniae (2 × 10 3 cfu fish −1 ). At the end of the 30 days feeding trial, there were no significant differences in final body weight, weight gain, feed conversion ratio, and hepatosomatic index among four groups. Plasma protein, total immunoglobulin (Ig), and lysozyme messenger RNA (mRNA) levels in fish fed on diets containing 1.0 and 2.0 g kg −1 of Sargassum sp. extract, however, became increased in a non-dose-dependent manner. When fish were exposed to the bacteria, at 24 h, there were significantly (p < 0.05) higher levels of hematocrit, red blood cell and white blood cell, Ig, and serum lysozyme in fish fed on diet containing 2.0 g kg −1 of Sargassum sp. extract than those of the fish fed the control diet, and the highest survival rate was also observed in this group. In addition, fish receiving the seaweed extract were able to suppress lipid peroxidation especially at 24-h post S. iniae challenge. These findings thus suggested that Sargassum sp. extract can be used as an immunostimulant in Asian sea bass.