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Effects of Salinity Changes on Growth Performance and Survival of Rohu Fingerlings, Labeo Rohita (hamilton, 1822)

Monjurul Islam
Department of Fisheries, University of Dhaka, Dhaka, Bangladesh

Dewan A Ahsan
Department of Fisheries, University of Dhaka, Dhaka, Bangladesh

Shankar C Mandal
Department of Fisheries, University of Dhaka, Dhaka, Bangladesh

Anwar Hossain
Department of Fisheries, University of Dhaka, Dhaka, Bangladesh

Abstract/ Executive Summary:

Labeo rohita was reared in laboratory condition at different salinities to observe the growth and survival. Three hundred and fifty rohu fingerlings were subjected to salinity regimes of 0, 2, 4, 6, 8, 10 and 12% for 90 days. Hundred percent survival was detected at 0 to 6% salinity while 100% mortality was recorded at 10 and 12‰ salinity. Fish showed high appetitive behavior to food between 0 to 4% salinities. Lowest feed conversion ratio was found in control group while the highest was detected at 6% salinity. On the other hand, decreasing trend of specific growth rate was observed in rohu fingerlings from 0 to 8% salinity. Similar average daily gain was found at 0 to 4% salinity. Significantly higher condition factor was found in rohu fingerlings reared at all duration at 8% salinity than those of other salinities (p<0.05). Thus the present study suggests that rohu fingerlings can be reared in coastal water with salinity of up to 6% with 100% survival rate and up to 4% salinity with similar growth rate as freshwater.

Keywords: Rohu fingerlings; Appetitive behavior; Salinity; Survival; Feed conversion ratio; Specific growth rate

Location: Department of Fisheries, University of Dhaka, Dhaka

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Carp fish

Objectives:

To investigate the effects of different salinity regimes on survival and growth of rohu fingerlings in laboratory condition.

Methodology:

The experiment was carried out at the aquatic laboratory of Department of Fisheries, University of Dhaka, Dhaka, Bangladesh. The fingerlings were acclimatized for a period of 72 hours prior to start of the experiment at the acclimatization tank. The brine solution was prepared in the circular tank by adding the commercial grade of NaCl until the selected level of salinity achieved. The salinity level was measured by salinity meter. Two factorial design with two replicates was applied to determine different growth parameters. Two factors were: duration (0, 15, 30, 45, 60, 75 and 90 days) and salinity (0, 2, 4, 6, 8, 10 and 12%). Seven sets of aquariums having 60 L of water capacity were stocked with 20 fish in each. The replacement of water from each aquarium was done for every 7 days by siphoning the bottom of the aquariums for 90 days rearing period. To determine the effects of salinity, fingerlings were exposed into 0, 2, 4, 6, 8, 10 and 12% salinity for 90 days rearing period in the Laboratory. For the purpose of conditioning 300 L static rectangular plastic tank was used. At first the fish fingerlings were released into the plastic tank at 0% salinity. After 48 hours of acclimatization 20 fish fingerling were released at the 0% salinity water while the rest of the fingerlings were kept inside the plastic tank at 2% salinity for the next 48 hours. After another 48 hours of acclimatization 20 fish fingerlings were released at the 2% the rest of the fingerlings were again kept inside the plastic tank at 4% saline water for the next 48 hours. Following this procedure the salinity was raised up to 12%. Finally the mortality, growth and other responses of the fish were observed at different salinities. Sampling was accomplished at the 15th, 30th, 45th, 60th, 75th and 90th day of the experimental period which included recording of length and weight of individual fish. Water quality parameters such as pH, dissolved oxygen (DO) and temperature were recorded in each alternative day. The fish were fed with fish feed meal of 50% Crude protein (CP) at 10% of total body weight. Weight gain was calculated by subtracting initial mean weight from the final mean weight. Specific growth rate (SGR), Feed conversion ratio (FCR), Average daily gain (ADG) and Condition factor (K) were calculated at the end of the each experiment for each salinity level using the formulae reported by Hopkins. SGR (%)=(In W₂–lnW₁) / (T₂-T₁) ×100, Where, W₁=Initial weight (g), W₂=Final weight (g), T₁=Initial time (day) and T₂=Final time (day); FCR=Feed (g) consumed by the fish / (W₂-W₁), Where, W₁=Initial weight (g)and W₂=Final weight (g); ADG=(W₂-W₁) / (T₂-T₁), Where, W₁=Initial weight (g), W₂=Final weight (g), T₁=Initial time (day) and T₂=Final time (day); K=(W/ L³)×100, Where, W=Weight (g)and L=Length (cm) Data were expressed as mean ± standard error of the means. General Linear Model (GLM) of two way ANOVA was used to analyze the data. Statistical software SPSS version 11.5 was used to analyze data with the levels of significance at p<0.05.

Source of Information: J Coast Dev 2014, 17:1; ISSN: 1410-5217 JCD

Article Link (Online Journal): http://dx.doi.org/10.4172/1410-5217.1000379

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The research revealed that rohu fingerlings can adapt to gradual increase of salinity. Normal growth was observed at salinity regimes of 0-4%. However, the most preferred salinity was 2%. In Bangladesh about 60 million people live in coastal zone (the coast line is about 710 km long). It is almost impossible to relocate the vast number of inhabitants from the coastal zone as the country is heavily overpopulated and tiny. Therefore, adaptation with the changed climatic condition is the best policy to combat the global climate change. In that aspect the finding of this study could be applicable in carp polyculture in saline water contaminated coastal ponds as rohu fish can be easily grown up to 4% salinity.

Knowledge Management: Journal