Seasonal variation of water quality and nutrient contents of Wallagoattu (Bloch & Schneider, 1801) in different freshwater habitats of Bangladesh

Abstract

The purpose of the study was to assess the levels and seasonal variation of physical, chemical properties and nutrient contents of Boal fish (Wallagoattu) collected from AshoolarBeel and Jamuneswari River in order to provide current information on habitats water characteristics, fish nutrient contents and hence propose suitable measures for sustainable management. This study was conducted from May 2015 to December 2015, covering among pre-monsoon, monsoon and post-monsoon periods. AshoolarBeel and Jamuneswari River are very important resource to peoples, stakeholders and has a fragile ecosystem that experiences rapid changes associated with natural and anthropogenic factors such as huge water abstraction for irrigation agriculture, fertilizer residues runoffs from the agro-based farms and sediments discharged.They are playing an important role in the regional economy and food security of the local people. Among different water quality parameters dissolved oxygen, transparency, pH, and depth varied significantly among the sampling sites. During the study period Air temperature (Mean ± SD) ranged between 27.42 ± 1.84 °C to 31.68 ± 1.12 °C atAshoolarBeel and 26.70 ± 1.48 °C to 31.66 ± 1.07 °C atJamuneswari River in the different season. Water temperature was found vary from 25.40 ± 2.75 °C to 30.30 ± 1.08 °C atAshoolarBeel and 26.10 ± 2.70 °C to 30.10 ± 1.03 °C atJamuneswari River in the different season in the study period. Mean (±SD) transparency values showed a peak of 49.45 ± 8.84 cm in post-monsoon and lowest values of 41 ± 14 cm in pre-monsoon both in the two habitats respectively. The water depth was showed very wide changes in each habitats as well as seasons. The depth of water column varied between 2.20 to 14.00 ft at AshoolarBeel and 2.00 to 14.00 ft respectively in the pre-monsoon and post-monsoon session. Mean (±SD) dissolved oxygen values for the two habitats a general decline as from pre-monsoon, with a peak value of 10.12 ± 1.5 mg/l in post-monsoon at AshoolarBeel and the lowest value of 6.22 ± 0.879 mg/l in pre-monsoon at Jamuneswari River. During these investigations, pH value was found to high (8.10) in pre-monsoon season in comparison to monsoon & post-monsoon season both in the two habitats. In the study, the maximum value of alkalinity 45.20 mg/l was recorded in the pre-monsoon in AshoolarBeel and the minimum value 27.45mg/l atJamuneswari River during post-monsoon period. Alkalinities in all sampling season were not similar. The study was also conducted to determine the chemical composition of Wallagoattubased on the moisture basis.Biochemical composition indicates the percentage of many important nutrients that are essential to the human body. Nutritional quality of an edible variety of fish is important for formulation of balanced food products. The maximum value of Moisture contents of Boal fish 79.03 % was reported in the post-monsoon at Jamuneswari River and the minimum value 72.38 % at AshoolarBeel during pre-monsoon period. The mean (±SD) values of ash contents were 2.43±0.46 %, 2.20±0.22 % and 2.55±0.67 % at AshoolarBeel and 2.31 ± 0.58%, 1.91 ± 0.88% and 2.76 ± 0.60% atJamuneswari River in the pre-monsoon, monsoon and post-monsoon period respectively. Protein contents were significantly higher in the post-monsoon and lower in the pre-monsoon period. The maximum value of protein contents of Boal fish 19.72 % was reported in the post-monsoon atJamuneswari River and the minimum value 16.82 % at AshoolarBeel during pre-monsoon period. In the present study, the range of lipid contents of the fish was found to vary from 3.10-5.14 %, 2.57-4.21% and 2.24-3.37 % atAshoolerBeel and 3.49-4.78 %, 2.63-4.17 % and2.02-3.83 %atJamuneswari River during experiment in the three different seasons. There was significant differences (P<0.05) of all the water quality parameters and nutrient contents observed among pre-monsoon, monsoon and post-monsoon period both at the Jamuneswari River and AshoolarBeel. But there was no significant differences show between the two different freshwater habitats except water depth in post-monsoon season. Seasonal influences of all the water quality parameters and nutrient contentswere more or less same for each habitat.The above findings have shown most of the parameters studied are within permissible limits of still exceed the enviable range given by some agencies and nutrient composition of the fish species might be a good source of protein in this study area.