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This study was to assess effects of the pretreatment in allplant based diets with microbial phytase on phosphorous utilization and growth performance of Nile tilapia (Oreochromis niloticus). Pretreatment trials were conducted using phytase at graded doses to determine the optimal dose of phytase. Available phosphorus (P) levels increased significantly with the increased doses of phytase and the dose of 1000 U kg )1 was most efficient. Based on the pretreatment trials, plant based diets for Nile tilapia were formulated by pretreating with phytase at 1000 U kg )1 . Experimental diets were supplemented with graded levels of mono calcium phosphate (MCP) at 25, 18.75, 12.5, 6.25 and 0 g kg )1 diet. In addition, there were three controls: one phytase control, one inorganic P control and one pretreatment control. The results showed that diets pretreated with phytase gave better growth performance, feed conversion ratio and protein efficiency ratio of Nile tilapia compared with the phytase control diet and pretreatment control diet (P < 0.05). There were no significant differences in growth performance of Nile tilapia between the inorganic control diet and phytase pretreated diets supplemented with MCP at 25, 18.75 and 12.5 g kg )1 (P > 0.05), which resulted in significantly better performance than those at 6.25 and 0 g kg )1 (P < 0.05). Dietary interaction effects of phytase were observed for phosphorus retention efficiency and phosphorus load. Apparent digestibility coefficient of P (ADCp) was improved significantly by phytase pretreatment (P < 0.05). No significant difference was detected on ADC of crude protein among all experimental diets (P > 0.05). KEY WORDS

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This study assessed the microplastic contamination of 3 most abundant sessile and intertidal invertebrates (Rock Oyster: Saccostrea forskalii, Striped Barnacle: Balanus amphitrite, Periwinkle: Littoraria sp.) in 3 beaches of the eastern coasts of Thailand. The results showed a significant accumulation of microplastics in the invertebrates at rates of 0.2-0.6 counts/g indicating higher pollution levels along the coastline. Filter feeding organisms showed comparatively higher accumulation rates of microplastics. Thus, contaminated bivalves pose potential health risks for seafood consumers. The plastic pollutant prevalence in sessile and intertidal communities was corresponded with pollution characteristics of contaminated beach habitats where they live. Thus, bivalves, gastropods and barnacles can be used as indicators for contamination of microplastics in the areas. This study also demonstrated the need for controlling plastic pollution in Thai coastal areas.

A 20-week feeding trial was conducted to determine whether increasing linolenic acid (18:3n-3) in vegetable oil (VO) based diets would lead to increased tissue deposition of 22:6n-3 in Nile tilapia (Oreochromis niloticus). Five isonitrogenous and isoenergetic diets were supplemented with 3% of either linseed oil (LO), a mixture of linseed oil with refined palm olein oil (PO) (LO-PO 2:1) and a mixture of refined palm olein oil with linseed oil (PO-LO 3:2) or with fish oil (FO) or corn oil (CO) as controls. The PO-LO, LO-PO and LO diets supplied a similar amount of 18:2n-6 (0.5% of diet by dry weight) and 0.5, 0.7 and 1.1% of 18:3n-3, respectively. Increased dietary 18:3n-3 caused commensurate increases in longer-chain n-3 PUFA and decreases in longer-chain n-6 PUFA in the muscle lipids of tilapia. However, the biosynthetic activities of fish fed the LO-based diets were not sufficient to raise the tissue concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 to those of fish fed FO. The study suggests that tilapia (O. niloticus) has a limited capacity to synthesise 20:5n-3 and 22:6n-3 from dietary 18:3n-3. The replacement of FO in the diet of farmed tilapia with vegetable oils could therefore lower tissue concentrations of 20:5n-3 and 22:6n-3, and consequently produce an aquaculture product of lower lipid nutritional value for the consumer.

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The total lipid content and fatty acid composition of the muscle tissue of tilapia (Oreochromis niloticus) and of hybrid red tilapia (Oreochromis sp.) from different culture systems and from the natural and artificial environment of Thailand were compared. Wild fish and fish reared under the most extensive conditions had a more favorable fatty acid profile for human consumption as they contained higher proportions of 18:3n-3, 20:5n-3, and 22:6n-3, higher n-3/n-6 PUFA ratios, and lower proportions of 18:2n-6. The muscle tissue of intensively cultured fish was characterized by increased fat deposition that was mainly saturated and monounsaturated fatty acids and 18:2n-6. It is undesirable for the consumer to reduce 20:5n-3 and 22:6n-3 in farmed tilapia and replace them with elevated 18:2n-6. It is recommended that the amount of 18:2n-6 in the feed of the intensively reared tilapia should be reduced by substituting vegetable oils rich in 18:2n-6 with oils rich in 18:1n-9 and/or 18:3n-3.