The effect of fluctuating temperature on muscle lipid composition was examined in 1.8 Kg steelhead trout fed 3 commercial diets with varying proportions (16.5 - 31% total) of Σω3 fatty acids and large differences (5×) in ω6:ω3 fatty acid ratios. Temperature was increased from 13.5°C to 18.0°C and then dropped back down to 13.5°C over a period of 12 weeks. Diet had no significant effect on growth or on total polyunsaturated fatty acid (PUFA) proportions in muscle tissue, but significant changes were observed in individual fatty acids. There was a greater response to changes in diet in the fatty acids than there was to changes in temperature. Muscle C20–C22 ω3PUFA and C18 unsaturated fatty acids reflected dietary inputs leading to very different (up to 40%) ω6:ω3 fatty acid ratios. Independent of diet, increasing temperature significantly increased total lipids and saturated fatty acids, especially 16:0, and decreased monounsaturated ones, especially 18:1ω9, as well as the PUFA 18:2ω6. The ω6:ω3 fatty acid ratio was also lowest at 18.0°C. Increasing total lipids, sterols and saturated fatty acids with increasing temperature, has important implications for both cultured and wild fish in terms of their nutrition, food quality for humans, and resource availability for aquafeeds.
Gross impact of water pollution and water borne pollutants on aquatic organisms and man has become a great concern to public health in the recent time. Since fish gills are indirect contact with the environmental medium and are very sensitive to changes in water quality while fish liver serves as gate-keeper to the entire body of fish. Therefore, the aim of this study was to evaluate the effects of pollutants from the polluted Asa River on the gills and liver histology of Clarias buthupogon and Heterobranchus longifilis. The sample included a total of 55 individuals (28 for C. buthupogon and 27 for H. longifilis). There was a recorded moderate to intense alterations of gill tissues. The most notable alterations were congestion of blood vessels, desquamation, swelling of pillar cell, hyperplasia and hypertrophy of the gill epithelium. Epithelial lifting of the basement membrane was common in virtually all sampled fish species, while circulatory disturbances were slightly pronounced. The liver showed congestion of central vein, degeneration of hepatocyte, sinusoidal distortion, cellular inflammation and necrosis. However, all histological alterations recorded in the gill and liver tissues were most likely to be caused by increased concentrations of certain pollutants from industrial, domestic and agricultural premises. Furthermore, these results represent an additional reason to proceed with a detailed monitoring of the Asa River and the wildlife therein, for the sake of public health.
The study of the effects of the protein level on the survival rate, growth performance and the cost of production of pre-maturing Clarias jaensis fingerlings was carried out for 90 days at the Teaching and Research farm (5°36'-5°44'; 5°37'- 5°- 44'LN; 9°94' -10°06'and 9°85' - 10°06' LE; altitude 1392 -1396 m) of the University of Dschang. The aim of this work was to improve the production of this fish by determining its protein requirements. For this purpose, 360 Fingerlings of Clarias jaensis with an average weight of 23 ± 1.8 g and Total length 13.95 ± 2.90 cm were divided into 4 batches corresponding to diet containing 30; 35; 40 and 45% crude protein in the feed. The fish were fed twice a day at 5% of the ichthyobiomass and the quantity of feed where readjusted each month after biometrical monitoring. Data collected were analyzed by using SPSS 20.0 to test the effect of protein level on survival, growth characteristics and food production cost. The results obtained revealed that the lowest survival rate (80.03 ± 2.5%) was recorded with the 30% protein ration and the highest (89.23 ± 1.72%) with the 45% protein level in the feed. Feed intake and total length were not affected by the protein level in the feed. The highest weight gain (89.33 ± 1.99 g), mean daily gain (0.99 ± 0.05 g), specific growth rate (1.75 ± 0.10%), K factor (0.98 ± 0.23) were recorded with fingerlings fed 45% of crude protein in the diet (P<0.05). The lowest feed conversion ratio (3.32 ± 0.1) and protein efficiency ratio (0.67 ± 0.20) was obtained with the ration containing 45% crude protein and the highest feed conversion ratio (4.04 ± 0.05) and protein efficiency ratio (0.84 ± 0.12) with 30% crude protein (P<0.05). The Lowest cost for the production of a kg of body weight (606.03 FCFA ± 10.44) was obtained with the ration containing 30% protein but no difference was recorded between different feed. The study revealed that in the formulation of feeds for the Clarias jaensis fingerlings, 45% of crude protein will optimize survival rate, growth performance and cost production.
Gill net (Locally called odakku vala) design variation, operational techniques, catch composition and selectivity analysis in Vembanad wetland, Kerala was examined between January 2020 to June 2021. Netting materials used for gill net construction in Vembanad Lake were monofilament, multifilament Nylon (polyamide). The Gill net length was 25-55 m with a hung depth of 2-3 m. Gill net was highly species specific and showed selectivity for shallow water species. Its durability ranged from 3.5 months to 2 years depending on the netting material and the environmental conditions where it is being operated. Gill net fishery is one of the main types of artisanal fishery practiced occupationally by the fishermen community of Kerala. The region so far is untouched with the introduction of mechanized fishing apart from small traditionalized improvements. The Gill net was used to catch the fishes of marketable size, small fingerlings which were either used as bait or dried. Instead of using lead or aluminium needles as sinkers many of them were used to carry normal electric wire without copper string inside which reduce their cost of purchase.
