Management of Euglenophytes Bloom in Fish Ponds and its Effect on the Growth of Common Carp (Cyprinus Carpio L.) as an Algal Meal

Abstract

As harmful effects of euglenophytes bloom on fish production, three experiments were conducted to investigate the management of euglenophytes bloom in fish ponds and its effect on the growth of common carp (Cyprinus carpio L.) as an algal meal during 2010-2012 in Rajshahi district, North-west part of Bangladesh. The first experiment was conducted to investigate the relationships of euglenophytes bloom to environmental factors in nine fish ponds for twelve months from July 2010 to June 2011. Among the ponds, three ponds with bloom were selected at Raighati in Mohanpur Upazila (BP-R), another three ponds with bloom at Yusufpur in Charghat Upazila (BP-Y) and three non-bloom ponds (NBP) at Meherchandi in Motihar Thana. The environmental factors (water temperature, dissolved oxygen, pH, NO3-N, NH4-N, PO4-P, Fe, Zn, Mn and Cu), soil organic matter, and planktonic algal community and density were examined monthly by using standard methods. There was no significant difference in water temperature among the study ponds (BP-R, BP-Y and NBP) but significantly lower dissolved oxygen and pH, higher concentrations of NO3-N, NH4-N, PO4-P, Fe, Zn, Mn, Cu and soil organic matter, higher density of euglenophytes, and lower density of cyanophytes, chlorophytes and bacillariophytes were recorded in BP-R and BP-Y as compared to NBP (P<0.05). The euglenophytes were occurred by three genera, Euglena, Phacus and Trachelomonas among which Euglena was the dominant genus. The density of euglenophytes in the bloom ponds showed an increasing trend from September (early autumn) and peaked in November (late autumn) and December (early winter). The density of these algae showed negative correlation with water temperature, dissolved oxygen and pH while positive correlation with NO3-N, NH4-N, PO4-P, Fe, Zn, Mn and Cu concentrations (P<0.05). In second experiment, an attempt was made to investigate the management of euglenophytes bloom by using duckweed and lime for five months from August to December 2011 in twelve euglenophytes bloom forming ponds at Raighati, Mohanpur Upazila under four treatments such as T1 (the ponds treated with duckweed), T2 (the ponds treated with lime), T3 (the ponds treated with both duckweed and lime) and T4 (the ponds without duckweed and lime) with three replications. The study ponds were stocked with the fish species comprising Labeo rohita, Catla catla, Hypophthalmichthys molitrix, Puntius gonionotus and Cirrhina mrigala at 60/dec. Water quality parameters, soil organic matter, algal community and density, and growth performances (in terms of mean weight gain, average daily weight gain and specific growth rate), gut contents and electivity index of the fishes were examined by using standard methods. The results showed that use of duckweed and lime in the euglenophytes bloom forming ponds had positive effects on water quality parameters, soil organic matter, euglenophytes density and growth of fish. Better water quality, lower density of euglenophytes and higher growth of fish were recorded in T3 as compared to other treatments (P<0.05). The results of the gut contents and electivity index revealed that grazing of fish had no significant effects in controlling euglenophytes bloom. The third experiment was conducted to investigate the effects of euglenophytes algae supplemented feed on the growth and carcass compositions of common carp (Cyprinus carpio L.) for 12 weeks feeding trail from August to October 2012. Four feeds containing 0 % (Feed-1, Control feed), 20% (Feed-2), 30% (Feed-3) and 40% (Feed-4) euglenophytes algae were used in combination with conventional fish feed ingredients (Rice bran and mustard oil cake). The study was carried out in 12 glass aquariums at the wet laboratory of the Department of Fisheries, University of Rajshahi, Rajshahi under four treatments such as T1(the fish group fed with Feed-1), T2 (the fish group fed with Feed-2), T3 (the fish group fed with Feed-3) and T4 (the fish group fed with Feed-4) with three replications. Nutritive values of euglenophytes algae and experimental feeds, physico-chemical parameters of water, growth performance and feed utilization (in terms of mean weight gain, average daily weight gain, specific growth rate, feed intake and feed conversion ratio) and carcass compositions of fish were examined by using standard methods. The chemical analysis showed that euglenophytes algae contained average 49.64% crude protein, 14.40% crude lipid, 15.96% total carbohydrate, 9.29% moisture and 10.41% ash, and the experimental feeds (four combinations) had different nutritional value. During the study period, physico-chemical parameters of water among the treatments did not show any significant difference (P>0.05) and remained within the suitable ranges for fish growth. The results showed that euglenophytes algae supplemented feeds had positive effects on the growth and carcass compositions as compared to the control feed. Significantly higher growth, improved FCR and better carcass nutrients recorded in T3 as compared to other treatments (P<0.05). The findings of the present research indicates that higher concentrations of nutrients and heavy metals under lower water temperature, dissolved oxygen and pH are responsible for euglenophytes bloom; use of both duckweed and lime is better for management of euglenophytes bloom; and euglenophytes algae could be used as a feed ingredient and 30% supplementation of these algae in the conventional feed is better for growth and carcass nutrients of common carp. More comprehensive investigations are required in long-term basis and future design including more ponds/aquariums would increase the statistical power in order to base conclusions on the effect of different treatments.