Technical advances have made possible the production of microalgal concentrate in paste form. Chaetoceros calcitrans was concentrated and made into an algal paste through centrifugation, chemical flocculation, and electrolytic flocculation. The paste can be stored up to three months when refrigerated, and is diluted with seawater for feeding to the tiger prawn, Penaeus monodon. This can also be done with other cultured diatoms, and they can be fed to other penaeid shrimp and other organisms such as the Sydney rock oyster and the Pacific oyster. The use of algal paste can simplify hatchery operations and reduce costs among hatcheries with no microalgal culture facilities.

Seaweeds account for nearly 30% of global aquaculture production by volume, and their cultivation provides important opportunities for employment and wealth generation, particularly in rural coastal communities. Eucheumatoids (Kappaphycus and Eucheuma spp.) are tropical red algae commercially cultivated as raw material for production of carrageenans, particularly in South-East Asia and the Western Indian Ocean region. Diseases and pests are major limiting factors in eucheumatoid production, particularly a condition known as ‘ice-ice’ disease (IID). IID is characterized by bleaching of the thallus followed by the disintegration of affected tissues, leading to a loss of biomass and reduced carrageenan yield. IID has been associated with unfavourable changes in environmental conditions, particularly an increase in sea water temperature and a decrease in salinity, and infection by opportunistic or pathogenic bacteria. However, given that no single or combined causal agents have been definitely identified, IID may be considered a complex pathobiotic syndrome in which multiple factors contribute to the development of disease signs. Here, we review current knowledge of the abiotic and biotic factors associated with the development of IID, and the strategies employed to mitigate economic losses resulting from disease outbreaks. We discuss syndromic diseases in other marine holobionts, particularly other red algae and corals, in relation to their similarity to IID, and suggest the application of comprehensive and complementary methodologies, including high-throughput sequencing and high-quality microscopy, for enhancing our understanding of the pathological and microbiological processes associated with IID signs.

This paper reports the first use of thin flakes (310–315 μm thick) formulated diets as feed for the abalone Haliotis asinina. The study compared noodles and flakes prepared using refined and unrefined diets developed earlier for H. asinina (Bautista-Teruel et al., J. Shellfish Res., 35, 2016, 633). Four treatment diets in triplicates (refined flakes, MBTr-F; refined noodles, MBTr-N; unrefined flakes, MBTur-F; and unrefined noodles, MBTur-N) were used in a feeding experiment conducted in a tank facility. After three months, abalone fed MBTr-F had significantly higher mean shell length and body weight (35.92 ± 0.36 mm, 9.24 ± 0.29 g) compared with those fed MBTr-N (34.63 ± 0.37 mm, 8.22 ± 0.28 g) and MBTur-N (34.23 ± 0.36 mm, 7.66 ± 0.26 g), but did not significantly differ with those fed MBTur-F (35.40 ± 0.30 mm, 8.57 ± 0.24 g). Likewise, abalone fed MBTr-F had significantly higher mean growth rates (5.31 ± 0.08 mm, 2.59 ± 0.06 g/month), compared with those fed MBTr-N (4.90 ± 0.19 mm, 2.26 ± 0.12 g/month) and MBTur-N (4.71 ± 0.02 mm, 2.07 ± 0.06 g/month), but did not significantly differ with those fed MBTur-F (5.11 ± 0.06 mm, 2.37 ± 0.04 g/month). Survival (96.67–98.89%) and FCR (2.2–2.5) did not significantly differ among treatment diets. Between the flaked diets, MBTur-F is the cheaper option. However, the use of this unrefined diet resulted in distinct turquoise abalone shell colour, not observed in those fed MBTr-F.

Nine concrete tanks (2 x 2 x 1 m) were stocked with tilapia fingerlings (abw = 3.3±0.9 g) and three stocking rates (50 fish/m², 100/m², and 150/m²) were tried. The rearing period lasted for 120 days. Fingerlings were fed commercial diet containing approximately 27% crude protein. The amount of feed was adjusted based on monthly weight samplings. Pre-filtered lake water pumped through gravity aerators into the tanks was used throughout the culture period. Although production was intensified, water agitators and similar mechanical implements were not employed to cut production costs. Results show that tilapia stocked at 50/m³ grew significantly heavier at 109.2 ± 8.0 g. This was significantly better (P<0.05) than fish stocked at 100 and 150/m³, which had basically the same final weight of 82.4 ± 1.8 g and 83.4 ± 8.7 g, respectively. Likewise, survival or recovery at harvest was highest at 92.8% for the stocking rate of 50 fish/m³. The results suggest that stocking at lower densities would result to bigger fish but a lower total yield per tank, or higher stocking densities would mean higher yield but smaller individual fish size at harvest. The rate of water flow through at harvest time was equivalent to 0.30 L/min/kg biomass at the highest stocking density of 150/m³, 0.40 L/min/kg biomass at 100/m³, and 0.60 L/min/kg biomass at the lowest density of 50/m³. Siddiqui et al. (1991) suggested a minimum of 0.50 L/min/kg biomass flow rate for intensive culture of tilapia, but this was generally for clean culture water, not like lake water whose quality varies naturally. After determining the optimum stocking density, a second experiment using bigger fingerlings (57.5±12.6 g) was conducted for 101 days to determine the ideal water flow rate in the system. Varying flow rates (10 liters per minute (Lpm), 15 Lpm and 20 Lpm) were evaluated at a fixed stocking density of 50 fish/m³. Feed ration was 5% during the first two months, 4% on the third month, and 3% thereafter. Tilapia size at harvest increased with increasing flow rate when stocked at 50 fish/m³. From an initial stocking size of 57.5 ± 12.6 g, biggest fish harvests were obtained in tanks with a flow through rate of 20 Lpm (152.2 ± 15.1 g) after 101 days of culture. However, this was not significantly different to fish grown in tanks at 15 Lpm (139.9 ± 7.6 g). Smallest fish harvests were obtained at 10 Lpm at 111.20 ± 8.3 mm. A similar trend was observed with fish length at 157.7 ± 15.5 mm, 150.8 ± 11.0 mm, and 142.1±17.6 mm for 20 Lpm, 15 Lpm, and 10 Lpm, respectively. Feed conversion ratio (FCR) ranged from 1.7 to 2.5 in all treatments. The rate of water flow through at harvest time was equivalent to 1.2 L/min/kg biomass at 20 Lpm, 0.6 L/min/kg at 15 Lpm (sufficient for Laguna de Bay water), and 0.4 L/min/kg at 10 Lpm flowrate. Except for a slight increase in ammonia levels (maximum 1.1 mg/L total ammonia nitrogen) towards the final two weeks of the rearing period, water quality in the culture tanks was generally within tolerable levels throughout the run. Thus, the quality of water from Laguna de Bay can safely support the stocking density used in the experiment. However, if stocking density is further increased, aeration may need to be provided because very low early morning dissolved oxygen levels (DO) were observed, especially in tanks with high stocking density. The significant amount of sludge, mainly fish feces and uneaten feeds, effectively trapped and collected from the settling apparatus, clearly demonstrated the apparatus efficiency. Effluent water was practically rid of solid wastes, and gravity aeration oxygenated the water before it was discharged back to the lake. Ammonia, pH and DO levels of the effluent water were similar to those recorded from the water in the header tank.

Laguna de Bay, the largest freshwater lake in the Philippines, experiences periodic blooms of the cyanobacteria Microcystis aeruginosa. The results of analysis for the presence of the hepatotoxin microcystins in bloom samples of this cyanobacteria from 1996, 1998, 1999 and laboratory cultures from 1997 isolates, based on the studies conducted at Binangonan Freshwater Station of SEAFDEC/AQD are presented. Twenty structural variants of the toxin have been isolated with microcystin LR (MC-LR) being the most abundant form. MC-LR contribution ranged from 22% to almost 100% of the total microcystins in the samples. Microcystis bloom in 1998 had MC-RR as the most dominant form of the toxin with almost 38% followed closely by MC-WR (23%) and MC-LR (22%). The harvest from 1996 had the highest total toxin concentration (4048 µg g^-1). Laboratory-cultured M. aeruginosa had even higher total toxin concentrations ranging from 11,472 to 12,160 µg g^-1. The presence of high microcystins concentrations in M. aeruginosa from Laguna de Bay has far reaching implications in terms of the use of this resource for fishery and domestic water supply.