The nutritional value and the possibilities of utilization of the aquatic weed, Nymphoides cristatum as feed for young Labeo rohita, were evaluated in terms of growth, conversion efficiency, specific activity of digestive enzymes, bio‐chemical composition of flesh and microbial composition of intestine (cellulolytic bacteria), in a 60‐day laboratory feeding trial. The daily dry matter (DM) intake of the control diet (FC) prepared with mustard oil cake:rice bran (3:7) and aquatic weed (FN) prepared with N. cristatum leaf meal was 4918 and 5948 mg, digestible DM of 4179 and 5185 mg and digestible energy (DE) of 53.56 and 84.33 kJ kg–1 fish, respectively. The specific growth rate was 3.18 and 3.8 with the control diet and the weed, respectively. Fish fed with the weed showed better average daily gain (ADG%), feed conversion ratio (FCR) and protein efficiency ratio (PER). The specific activity of proteolytic and amylolytic enzymes showed significant increase (P < 0.001) in fish fed with the weed. Culture of intestinal mucosa revealed the presence of cellulolytic bacteria, the count per cm being higher in the intestinal bulb (3.70 × 104–4.32 × 104) followed by middle intestine (2.16 × 104–2.29 × 104) and posterior intestine (1.26 × 103–1.35 × 103) in the fish fed with the diet FN as compared with the diet FC. The preliminary study indicate the possibilities of incorporation of the aquatic weed, N. cristatum in the diet of L. rohita substituting conventional feed ingredients.
Trypsin inhibitor from water fern (Azolla pinnata R. Br.) was isolated and characterized. Extraction of Azolla leaf meal in NaCl (0.15 M) rendered a higher recovery of trypsin inhibitor compared to other solvents tested (P < 0.05). The extraction time affected the inhibitor recovery significantly (P < 0.05). The extraction time of 3 h was optimum for the recovery of trypsin inhibitor. Based on inhibitor activity of a zone separated by electrophoresis, the molecular mass of the inhibitor from Azolla leaf was 21 kDa. The partially purified inhibitor was heat stable up to 10 min at 90C, at pH 7.0. High activity was also retained over a wide pH range (4–8) at 37C.
During the present study the average annual catch of Penaeus monodon during 2011 -2013 was 281.29±9.67 ton, which contributed 0.41 % to the total trawl net catches at Digha coast. The average catch rate was 43.41 kg/h. The percentage of P. monodon to total shrimp catch was 1.91% in trawl landings at Digha coast. Monthly mean landings were 28.13±0.97 t from the trawl nets. Peak landings were observed from June to November with a maximum of 56.46±1.97 t in September and lean landings were observed from December to March with a minimum of 6.12±0.21 t.
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