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Effects of Salinity on the Growth, Survival and Proximate Composition of Pangas, Pangasius Hypophthalmus

Shankar Chandra Mandal
Department of Fisheries, University of Dhaka, Dhaka-1000, Bangladesh

Shahin Kadir
Department of Fisheries, University of Dhaka, Dhaka-1000, Bangladesh

Anwar Hossain
Department of Fisheries, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

Climate change induced salinity intrusion has a global and local effect on the aquaculture production. Thai-Pangas (Pangasius hypophthalmus) has become one of the cheapest protein sources in Bangladesh because of its wide range of environment tolerance, excellent growth and survival rate. Present study was thus conducted to measure the effects of salinity on the growth performance and survival of pangas. For the determination of the effect of salinity on growth and survival, 15-day old fingerlings were reared in 0, 2, 4, 6, 8, 10, 12, 14 and 20‰ for 60 day at laboratory condition. All fish fingerlings in treatment with 20‰ salinity died within 6 hours of stocking while 62.5% mortality was found within 6 hours at 14‰ salinity. No mortality was detected in other treatment groups. Significantly higher specific growth rate was detected at 0, 2 and 4‰ salinity than that of 12 and 14‰ salinity. No significant change in food conversation ratio was found among treatments. No significant difference was observed on proximate composition between and within treatments. Water quality parameters include temperature, dissolved oxygen and pH were 27.23 ± 0.02 °C, 8.33 ± 0.05 mg/L and 8.05 ± 0.03, respectively throughout the experimental period. Thus, the present study suggests the suitability of pangas fingerlings at up to 4‰ saline water with desirable growth rate.

Keywords: Salinity intrusion, Thai Pangas, Feed conversion ratio, Water quality

Location: Aquatic Laboratory of the Department of Fisheries, University of Dhaka, Bangladesh.

Start Date: 00-00-2011

End Date: 00-00-2012

Program Area: Animal Health and Management

Commodity: Pangus

Objectives:

To find out the maximum salinity that pangas can tolerate without affecting survival and proximate composition.

Methodology:

Experimental fish: Pangas, Pangasius hypophthalmus (4.68 ± 0.15 g and 3.79 ± 0.25 cm) was used as experimental fish which was obtained from the Nirob Fish Hatchery at Mymensingh and transported to Aquatic Laboratory of the Department of Fisheries, University of Dhaka, Bangladesh. Fingerlings were acclimatized in rectangular tanks at freshwater (salinity; 0‰, temperature; 27.17 ± 1.97 °C, pH; 8.14 ± 0.24 and DO; 8.33 ± 0.33 mg/L) for two weeks prior to conduct the experiment. All the fish fingerlings showed a normal behavioral pattern during this period. Experimental system: The experiment was conducted in 40L aquaria, each was stocked with 10 fish fingerlings and the initial weight of fingerlings showed no significant difference among treatments. Pond water was used in the present study. The experiment was conducted during the year 2011-2012. Experimental Design: Nine treatments were conducted with triplicate groups. The range of salinity selected in this experiment was based on the environmental salinity, as Bangladesh has the huge resource of both freshwater and saline water and has a good connected area between freshwater and saline water. The river flow system is very much helpful to regulate the salinity level. The aquaria were covered with wooden shade to prevent fish from jumping out, and continuous aeration was provided to maintain dissolved oxygen near saturation levels. In each aquarium, 50% of water volume was renewed every alternative day with water of the salinity selected for the treatment. For the purpose of conditioning 300L static rectangular plastic tank was used. At first, the fish fingerlings were released into the plastic tank at 0‰ saline water. After 48 hours of acclimatization 10 fish fingerlings were released in the 0‰ saline water and the rest of the fingerlings were kept inside the plastic tank at 2‰ saline water for the next 48 hours. After another 48 hours of acclimatization 10 fish fingerlings were released in the 2‰ saline water and the rest of the fingerlings were again kept inside the plastic tank at 4‰ saline water for the next 48 hours. Accordingly, the salinity was raised up to 14‰. Finally uprising of salinity from 14 to 20‰ was made which was referred as mega dose. During the acclimatization period, salinity was raised up to 2‰ per 48 hours for all treatments by adding required amount of salt (from Coxes Bazar) for each of the following salinity groups: 0, 2, 4, 6, 8, 10, 12, 14 and 20 ‰. Pangas fingerlings were exposed to these salinity for 60 days. Salinity in each tank was measured once daily. Maintenance of aquaria and sampling: At 20-day interval length and weight of each fish of each treatment were taken and fish were fed with commercially available pangas feed @ 5% of their total weight twice a day. Uneaten feed was removed from the aquarium by siphon from the floor. Fifty percent water was exchanged every alternative day and continuous aeration was provided throughout the experimental period. Fish weight and length were recorded to determine the feed efficiency, feed conversion ratio, condition factor, average daily gain and protein efficiency ratio. Sampling was done at 20^th, 40^th and 60^th day of the experiment. Growth study: Condition factor (K) was calculated by the following formula as suggested by Hile (1936); K = (w/L³) × 100; Where, K- condition factor; W- body weight in grams and L- body length in centimeters. Average daily gain was determined by the following formula: ADG = (W₂-W₁)/t₂-t₁ where, W₂, final weight, W₁, initial weight, t₂-t₁ duration of experiment. Specific growth rate (SGR %) was calculated as the percentage increase in weight per animal per day as suggested by Hopkins (1992), i.e. SGR (%) = LnW_t – LnW_l / (T – t) × 100. Where, LnW_t= Natural log of weight at time T; LnW_l Natural log of initial weight; T: Time t; Initial time. Food conversion ratio (FCR) was calculated from the weight (Kg) of feed that are used to produce one Kg of whole fish. Food conversion ratio (FCR) was determined by the following formula: FCR = Feed consumed by the fish (Kg) (dry weight basis)/ Live weight of the fish (Kg). Survival rate of fish fingerlings was also determined. Water quality monitoring: Salinity levels were monitored by using the salinometer (YSI, Japan), pH and DO with pH and DO meter (ITOSENCE, Japan) twice a week. Proximate analysis: Proximate composition was analyzed according to AOAC (1990) with some modifications as described below. Briefly, for the determination of moisture content 5g of sample was dried in an oven at 105 ºC for complete evaporation of moisture. After complete dryness of the sample the loss of moisture was calculated as percent moisture content. For the determination of lipid content, the dried sample left after moisture determination was finely ground and about 0.5g were taken in a mortar and macerated with fine sand. Lipid content was then determined using chloroform-methanol method. Ash content was determined from 2g of sample which burnt over a flame until it charred and then placed in a muffle furnace at 550 ºC temperature for complete combustion. White residue was weighed, and ash content was determined. Crude protein content was determined using the standard microKjeldahl method. Statistical analysis: Data were analyzed by using SPSS (version 11) with a level of significance at p<0.05. One-way ANOVA was done, and significant results were further analyzed using Tukey Test in order to determine ranking and significant differences between treatment means.

Source of Information: Bangladesh J. Zool. 48(1): 141-149, 2020

Article Link (Online Journal): DOI: https://doi.org/10.3329/bjz.v48i1.47883

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Pangas is one of the economically important fish species in Bangladesh. The salinity intrusion can result in the reduction of production of this species. However, the results of this study have shown that pangas fingerlings can easily survive at salinity up to 12‰. The growth and feed conversion efficiency was found to remain same at salinity of 4‰. However, the growth of pangas has been found to be negatively correlated with increasing salinity above 4‰. The study suggests the necessity of large-scale trial on survival and growth of pangas in saline water.

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