Production of organic grass carp (Ctenopharyngodon idella) and GIFT tilapia (Oreochromis niloticus) using napier grass, Pennisetum purpureum

This study was conducted to examine the growth and production of grass carp and tilapia cultured organically using napier grass in Bangabanbhu Sheikh Mujibur Rahman Agricultural University, Bangladesh from March-June, 2013. Three stocking ratios were tested: grass carp at 0.6 fish/m2 with GIFT tilapia at 0.3 fish/m2 (T1), grass carp at 0.6 fish/m2 with GIFT tilapia at 0.6 fish/m2 (T2), grass carp at 0.6 fish/m2 with GIFT tilapia at 0.9 fish/m2 (T3) and grass carp only at 0.6 fish/m2 as control (T4). Chopped fresh napier grass leaf was the sole nutrient input and provided twice daily. The water quality parameters were within suitable ranges for fish culture. Grass carp attained a daily growth increment ranging from 2.80-3.73 g/day and GIFT tilapia from 1.30-1.86 g/day. The combined yields was significantly higher (P<0.05) in stocking ratio of 1:1 (2.72 t/ha/90 days) compared to other stocking ratios. The result indicates on the basis of benefit-cost-ratio that the farmer’s income will be around double or more in the combined production of organic grass carp and tilapia with stocking ratio of 1:1 than the other stocking ratios. The density of grass carp should be further studied

Production of organic grass carp (Ctenopharyngodon idella) and GIFT tilapia (Oreochromis niloticus) using napier grass, Pennisetum purpureum

This study was conducted to examine the growth and production of grass carp and tilapia cultured organically using napier grass in Bangabanbhu Sheikh Mujibur Rahman Agricultural University, Bangladesh from March-June, 2013. Three stocking ratios were tested: grass carp at 0.6 fish/m2 with GIFT tilapia at 0.3 fish/m2 (T1), grass carp at 0.6 fish/m2 with GIFT tilapia at 0.6 fish/m2 (T2), grass carp at 0.6 fish/m2 with GIFT tilapia at 0.9 fish/m2 (T3) and grass carp only at 0.6 fish/m2 as control (T4). Chopped fresh napier grass leaf was the sole nutrient input and provided twice daily. The water quality parameters were within suitable ranges for fish culture. Grass carp attained a daily growth increment ranging from 2.80-3.73 g/day and GIFT tilapia from 1.30-1.86 g/day. The combined yields was significantly higher (P<0.05) in stocking ratio of 1:1 (2.72 t/ha/90 days) compared to other stocking ratios. The result indicates on the basis of benefit-cost-ratio that the farmer’s income will be around double or more in the combined production of organic grass carp and tilapia with stocking ratio of 1:1 than the other stocking ratios. The density of grass carp should be further studied

Changes in Physicochemical, Microbiological, and Sensory Properties of Sun-Dried Mystus vittatus During Storage at Ambient Temperature

The objective of this study was to investigate the changes in physicochemical, microbiological, and sensory properties of sun-dried Mystus vittatus during storage at ambient temperature. The fish was dried under sun exposure on bamboo mats for 5–6 days until the moisture content reduced to approximately 10–15%. The dried fish was then packed into airtight polyethylene bags and stored at ambient temperature (24 to 29 °C) for 90 days. The physical and sensory properties revealed that the dried fish was acceptable for human consumption for up to 60 days. The pH value slightly decreased from 6.42 to 5.95 during the storage period. The moisture content increased significantly (p < 0.05), while no significant difference was observed for the protein, lipid, and ash contents (on a dry matter basis) with the increase in the storage time. The peroxide value, acid value, and conjugated dienes of the lipids increased significantly during the storage period. The microbial load also increased with the increase in the storage period. The results of this study suggest that the product was slightly oxidized during the storage period and could be stored for up to two months

Spatio-Temporal Variation of Flushing Time in the Sumjin River Estuary

Flushing is a very complicated process in estuarine environments. In order to examine the effects of tidal amplitude, river discharge, and stratification on the spatially varying flushing time of the Sumjin River Estuary (SRE), 24 longitudinal salinity transects were obtained during spring and neap tides from August 2004 to April 2007. The widely accepted freshwater fraction method has been used to calculate the flushing time for multiple estuarine segments using a spatially varying freshwater fraction. The effects of tidal amplitude, river discharge, and stratification on estuarine flushing were identified reasonably well by the spatially varying time scale. The flushing time appears to be close to the semidiurnal (M2) tidal period during spring tide, but it is twice as long during a neap tide near the mouth. The flushing time increases in the central regions with a decrease in the tidal amplitudes and reduces in the inner-most regions owing to the strong influence of gravitational circulation. A linear function negatively relates estuarine flushing to the tidal amplitudes near the mouth of the estuary, whereas a power-law function relates estuarine flushing to the freshwater inflow near the head. In addition, strong stratification induced by freshwater discharge and small tidal amplitude exerts dominant control to reduce the estuarine flushing in the central and upper regions of the estuary during a neap tide

The calculation of flushing time for the upper Pasur River Estuary, Bangladesh

Estimation of estuarine flushing time, a time required to transport of pollutants or any other properties from estuaries to the coast, is very important for its resource management. In this study, we estimated flushing time (T) of the upper Pasur River Estuary (UPRE) for understanding the water quality condition in the dry and wet seasons. High-resolution salinity data were collected from the PRE at high water in the dry and wet seasons in 2014 and 2019. Flushing time was calculated using the freshwater fraction method (FFM) as well as e-folding flushing time scales was estimated empirically using the salinity (non-reactive conservative) and monthly river discharge data. System flushing during the dry season was thirteen times weaker than flushing during the wet season owing to decreasing river discharge by nearly 94%. In addition, the daily exchange volume was decreased by eight times during the dry season than during the wet season. As a consequence, the conditions of the UPRE are more dynamic during the wet season due to receiving huge amount of river discharge. During the dry season, only the e-folding time scales showed higher values in the salinity maximum zone (salt plug area). This implied that the e-folding time scale is an empirical approach and was able to encompass the tidal dispersion process whereas the FFM was unable to include that process. As the PRE is a macrotidal estuary, the tide assists to flush dissolved substances from the UPRE to the coast during the dry season having negligible river discharge. In addition, there was no significant variation in water quality parameter between the salt plug area (SP) and downstream of salt plug area (DSP) during the dry season. In order to have more accuracy, a three-dimensional hydrodynamic model would be useful to compute estuarine time scales precisely.N

Use of Urban Open-waterbody to Enhance Fish Production through Cage Culture

The purpose of the experiment was to examine the effect of cage fish culture on the growth and production performances of Shing (Heteropneustes fossilis), Pabda (Ompok pabda) and Gulsha (Mystus cavasius). The stocking density for each fish species was 100 fish/m3. Cages with Shing, Pabda and Gulsha were treated as T1, T2 and T3, respectively. Fishes were fed with artificial diet at the rate of 5-10% of body weight. The experiment was carried out in cages in the Beel from June to November 2019. The study revealed that water quality parameters were not varied significantly (p > 0.05) among the treatments. The growth and production performance were significantly (p < 0.05) higher for Pabda cage culture followed by Gulsha and Shing cultures in cages. Therefore, the total net return (BDT 17,028) and benefit cost ratio (2.48) were significantly (p < 0.05) higher for Pabda fish considering cost benefit analysis. It was concluded that, among the three different fish species, high-valued Pabda is highly acceptable candidate for cage farming in Belai Beel area and cage farming in urban open waterbodies is a promising approach to increase the total fish production to improve the social and economic status of fish farmers. [J Bangladesh Agril Univ 2023; 21(1.000): 75-85

Fish Diversity in Relation to Salinity Gradient in the Meghna River Estuary, Bangladesh

Variation in salinity is one of the major environmental factors influencing the species diversity of fish in an estuary. Therefore, evaluating the relationship between salinity and species diversity is important. In this study, fish diversity was assessed by fish sampling and visiting local fish markets from February to November 2021. Mean salinity was 10.59 psu (Practical Salinity Unit) and 0.46 psu during the dry and wet seasons, respectively. Harpadon nehereus, Odontamblyopus rubicundus and Pseudapocryptes elongatus species were found as polyhaline (0.06~18.1 psu) species. Anguilla japonica and Arius gagora were abundant in brackish water conditions (0.35~14.2 psu). However, Acanthopagrus latus and Setipinna phasa were found in freshwater conditions (0.06~0.11 psu). The suitability index indicates that commercially important fish species such as Liza parsia, Macrobrachium rosenbergii, Mugil cephalus, Penaeus monodon and Scylla serrata can be used for mariculture during the dry season, and Acanthopagrus latus, Pethia canius and Setipinna phasa during the wet season. Overall, these findings suggest that salinity, water temperature, and chlorophyll-a had a significant (p < 0.05) effect on the fish distribution and assemblage composition in the study area. This finding will be helpful in developing policies for the conservation and management of the aquatic resources in the coastal zone to enrich the blue economy

Heavy Metal Pollution Reduced the Potentiality of Pen Culture in the Wetland Aquaculture in an Urban Area of Bangladesh

The Belai beel serves as an important aquatic resource for the livelihood of the local community of the Gazipur district in Bangladesh. However, water pollution in recent times, mainly from industrial wastes and sewage effluents, may disrupt its aquatic environment. Thus, the purpose of the present study was to assess the potential area of pen fish culture in the Belai beel. The study was performed in the Rajbagan (L1), Kamaria (L2) and Rewla (L3) areas of the Belai beel. Grass carp, silver carp, common carp, catla and rui of 20&ndash;30 cm in size were stocked at a rate of 15,000 fish/ha and reared for 150 days in pens installed in the L1, L2 and L3 areas, respectively. The fishes were fed with mustard oil cake and rice bran. Maximum fish production was found in Rewla (12.97 ton/ha/150 days) compared to Rajbagan (8.85 ton/ha/150 days) and Kamaria (10.67 ton/ha/150 days) due to it having comparatively good quality water. There were significant differences in metal ion concentrations (p &lt; 0.05) among the three fish pens. In the Rajbagan area, concentrations of Cd and Cu in the water coming from the industrial effluent canal exceeded the acceptable limit. Results indicated that the Rewla area was better than Rajbagan and Kamaria due to it having relatively good quality water for pen fish culture

Heavy Metal Pollution Reduced the Potentiality of Pen Culture in the Wetland Aquaculture in an Urban Area of Bangladesh

The Belai beel serves as an important aquatic resource for the livelihood of the local community of the Gazipur district in Bangladesh. However, water pollution in recent times, mainly from industrial wastes and sewage effluents, may disrupt its aquatic environment. Thus, the purpose of the present study was to assess the potential area of pen fish culture in the Belai beel. The study was performed in the Rajbagan (L1), Kamaria (L2) and Rewla (L3) areas of the Belai beel. Grass carp, silver carp, common carp, catla and rui of 20–30 cm in size were stocked at a rate of 15,000 fish/ha and reared for 150 days in pens installed in the L1, L2 and L3 areas, respectively. The fishes were fed with mustard oil cake and rice bran. Maximum fish production was found in Rewla (12.97 ton/ha/150 days) compared to Rajbagan (8.85 ton/ha/150 days) and Kamaria (10.67 ton/ha/150 days) due to it having comparatively good quality water. There were significant differences in metal ion concentrations (p < 0.05) among the three fish pens. In the Rajbagan area, concentrations of Cd and Cu in the water coming from the industrial effluent canal exceeded the acceptable limit. Results indicated that the Rewla area was better than Rajbagan and Kamaria due to it having relatively good quality water for pen fish culture

Dominant phytoplankton groups as the major source of polyunsaturated fatty acids for hilsa Tenualosa ilisha in the Meghna estuary Bangladesh

The tropical estuarine ecosystem is fascinating for studying the dynamics of water quality and phytoplankton diversity due to its frequently changing hydrological conditions. Most importantly, phytoplankton is the main supplier of ω3 polyunsaturated fatty acids (PUFA) in the coastal food web for fish as they could not synthesize PUFA. This study evaluated seasonal variations of water quality parameters in the Meghna River estuary (MRE), explored how phytoplankton diversity changes according to hydro-chemical parameters, and identified the major phytoplankton groups as the main source of PUFA for hilsa fish. Ten water quality indicators including temperature, dissolved oxygen, pH, salinity, dissolved inorganic nitrogen (DIN = nitrate, nitrite, ammonia) and phosphorus, dissolved silica and chlorophyll-a were evaluated. In addition, phytoplankton diversity was assessed in the water and hilsa fish gut. Principal component analysis (PCA) was used to analyze the spatio-temporal changes in the water quality conditions, and the driving factors in the MRE. Four main components were extracted and explained 75.4% variability of water quality parameters. The most relevant driving factors were dissolved oxygen, salinity, temperature, and DIN (nitrate, nitrite and ammonia). These variabilities in physicochemical parameters and dissolved inorganic nutrients caused seasonal variations in two major groups of phytoplankton. Peak abundance of Chlorophyta (green algae) occurred in water in nutrient-rich environments (nitrogen and phosphorus) during the wet (36%) season, while Bacillariophyta (diatoms) were dominant during the dry (32%) season that depleted dissolved silica. Thus, the decrease of green algae and the increase of diatoms in the dry season indicated the potential link to seasonal changes of hydro-chemical parameters. The green algae (53.7%) were the dominant phytoplankton group in the hilsa gut content followed by diatoms (22.6%) and both are contributing as the major source of PUFAs for hilsa fish according to the electivity index as they contain the highest amounts of PUFAs (60 and 28% respectively)