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Notes: Four different fertilization frequencies, namely twice per week, once per week, twice a month and once a month, were used in ponds to assess their effects on nutrient release, pond productivity and fish biomass. All ponds received the same total fertilizer inputs during the experimental period of 60 days (cow dung 208.3 kg ha−1 week−1, TSP 9.8 kg ha−1 week−1, urea 6.0 kg ha−1 week−1). Studies have revealed that the highest values of fish biomass, specific growth rate (SGR), net primary productivity (NPP), plankton population and nutrients were observed in the ponds that were fertilized twice a month. A strong and significant correlation of fertilization frequency was observed with dissolved oxygen, biochemical oxygen demand (BOD), alkalinity, nutrient release, NPP, plankton density (no. L−1), fish biomass and SGR. The linear relationship between NPP and fish biomass/SGR for all the ponds was strong (r2= 0.88). Sediment chemistry revealed that O-PO4, NO3-N, organic carbon and electrical conductivity (EC) increased significantly (P〈0.05) with a decrease in the frequency of fertilization, while alkalinity and calcium were high in ponds that were fertilized twice a month.

Notes: To study the effect of four different raw and hydrothermically processed leguminous seeds, namely Glycine max (soybean), Vigna radiata (moong), Vigna ungiculata (cowpea) and Cyamopsis tetragonaloba (guar) on growth in the fingerlings of Cirrhinus mrigala (mrigal) and Labeo rohita (rohu), two experiments were conducted. The first experiment was conducted under laboratory conditions (LD 12:12 at 25 °C) and the mrigal fingerlings were fed @2% BW d−1 for 30 days. Before using the seeds as feeds, they were hydrothermically processed (15 lbs at 121 °C for 15 min) for the elimination of antinutrient factors (ANF). The results indicate that 15 minute autoclaving significantly reduces the trypsin inhibitor activity. Phytase-phosphorous and tannins were also analysed from raw and treated beans. Studies on mrigal have revealed that weight gain was significantly low (P 〈 0.05) in the fish fed on raw beans compared with the fingerlings fed on processed bean proteins. Among the various raw diets used, significantly highest growth (P 〈 0.05) was observed in fish fingerlings fed on raw moong, followed by raw soybean, cowpea and guar. On the other hand, when beans were processed, the highest growth was observed in fingerlings fed on processed soybean. Studies have further revealed that hydrothermal processing also affected the values of the feed conversion ratio, gross conversion efficiency, protein efficiency ratio, gross protein retention, gross energy retention and ammonia excretion. Proximate composition of the carcass revealed high accumulation of protein, fat and energy in fingerlings fed on processed soybean in comparison with other diets. Keeping in view the higher weight gain in fish fed on hydrothermically processed bean proteins, only processed bean diets were fed to the fingerlings of mrigal and rohu stocked in fish ponds (experiment 2). A significant (P 〈 0.05) increase in mean fish weight, and specific growth rate was observed in fingerlings fed on hydrothermically processed soybean, followed by moong and cowpea. Weight gain for mrigal fingerlings remained significantly low in comparison to the rohu fingerlings fed on similar diets. An investigation on the effects of feeds on water quality parameters indicate that the trophic status of the ponds where soybean was used as fish feed remained high in comparison to the other treatments. A significant positive correlation of nutrients, NPP and plankton population with fish growth was also observed.

Notes: The present study attempts to assess the potential of artificial substrates to enhance fish production in inland saline groundwater ponds through periphyton production. Grey mullet, Mugil cephalus, was cultured for 100 days in ponds with substrate (treatment ponds) and without substrate (control ponds). To enhance the surface area, bamboo poles were used as substrate. The periphyton population, pigment concentration and hydrobiological characteristics of pond water were monitored. The studies revealed little difference in most of the water quality parameters observed in the two treatments. However, turbidity (27.0 ± 0.1–35.0 ± 0.1 Nephalo Turbidity Unit (NTU)), chlorophyll ‘a’ (6.6 ± 0.6–7.6 ± 0.6 μg L−1), plankton population (phytoplankton 8.4 × 103–9.4 ×103 numbers L−1; zooplankton 4.0 × 103–5.1 × 103 numbers L−1) and NH4–N (2.0 ± 0.2–2.3 ± 0.1 mg L−1) were high in the treatment with no additional substrate; however, in the treatment with substrate the total Kjeldahl nitrogen (9.8 ± 0.8–10.8 ± 0.7 mg L−1) and o-PO4 (0.1 ± 0.01–0.1 mg L−1) remained significantly (P 〈 0.05) higher. Highest periphyton biomass in terms of dry matter (DM) (0.8 ± 0.01–1.4 ±0.01 mg cm−2), ash free DM (0.4 ± 0.0–0.6 ± 0.01 mg cm−2), chlorophyll ‘a’ (3.1 ± 0.2–8.1 ± 0.8 μg cm−2) and pheophytin ‘a’ (1.9 ± 0.4–3.9 ± 0.5 μg cm−2) was observed at 50 cm depth in ponds provided with additional substrate. Fifteen plankton genera showing periphytic affinity colonized the bamboo substrates. Fish growth (mean fish weight 524.3 ± 8.7 g and SGR 2.5 ± 0.1) was significantly (P 〈 0.05) higher in ponds provided with additional substrate compared with control ponds (387.2 ± 6.0). Length–weight relationship (LWR) (W = cLn) also showed that the exponential value (‘n’) of length was high in substrate-supported ponds (n = 2.36) in comparison with controls (n = 1.09). These studies suggest that a periphyton-supported aquaculture system can be used successfully for the culture of herbivorous brackishwater fish species like M. cephalus in inland saline groundwaters and thus could contribute to the development of sound and sustainable aquaculture technology.