MATERIALS AND METHODS

Study area: For this experiment, an adjacent pond was used which located at Noakhali Science and Technology University (22°47 31 N 91°06 07 E) in Bangladesh and conducted during the period from 07 August to 13 October, 2017 for 9 weeks.

Experimental design: For nine weeks, the experiment was performed in an enclosure. Treatments 1 (T₁) and 2 (T₂) were used in the experiment, with feed rates of 10 and 7% of the fish's body weight, , respectively. Those two procedures were carried out in two separate cages with a 0.0723 decimal area and dimensions of 8×4×4 feet each. Between the cage and the embankment, there was a gap of 100 cm.

Preparing the water body before setting the cage: Manual uprooting of rooted weeds in the pond embankment. The hand net was used to keep track of floating weeds. For weed control, no chemicals were used. During the entire experiment, aquatic insects and other potentially harmful species like crabs were manually monitored. The installation of a bamboo pile in the dike helped to prevent soil erosion. The bottom was cleaned of excessive sedimentation.

Installed the cage: Bamboo, nylon net and jute fibre were used to make the cages which were all readily available in the region. The cage was designed to hold a one-meter distance between it and the dike. The pond bottom and the net bottom are separated by one foot.

Stocking of fry: The average length and weight of 40 days old fry were 9.60±.83 cm and 25.4±1.63 m, respectively, which are collected from a nearby fish hatchery. During the morning, fry were transported in an oxygenated polybag. Three days after setting up the experimental enclosure, the fry was acclimatized using the same pond water as the experiment. For both procedures, fish fry was stocked at a density of 20 per cage in Table 1.

Management of feeding: Fish meal, mustard oil cake, wheat flour, cornflower, rice bran, bone meal and starch were used in this experiment to create a sinking diet. During the formulation of the feed, the diameter size was kept constant at 2.00.3 mm. The diet used in the experiment had a nutritional composition of 94% Dry Matter (DM), with 31.6% Crude Protein (CP), 37.8% Crude Fiber (CF), 7.1% fat and 13.9% ash in Table 2. In this experiment, the protein was determined using the Kjeldahl method, fat was determined using the Soxhlet method, moisture was determined using the oven drying method, fibre was determined using the acid detergent method and ash was determined using the muffle furnace method. Directly thronging from hand, the feed was spread uniformly over the surface of the water inside the cage. The first half of the ration was provided at 8 am and the second half was provided at 4 pm. The amount of feed to be given adjusted after calculating the biomass of the cage every week.

Sampling and measurement: A scope net was used to capture the fish and a scale and a digital balance (Lutron GM-600.0 g×0.1 g) were used to measure the length and weight of each fish. To reduce sampling error, 30% of the total fish were sampled at each period. A pH meter (model: HANNA-HI96107) was used to calculate the pH of the water. A portable DO meter (Lutron-DO-5509) was used to measure dissolved oxygen twice a week The following formula was used to measure growth efficiency (weight and length), survival rate, Specific Growth Rate (SGR) and Feed Conversion Ratio (FCR) in this experiment¹⁴:

Statistical analysis: All data were subjected to make graph and table using MS Excel.

RESULTS AND DISCUSSION

Water quality parameters: Physical, chemical and biological environmental parameters were interrelated in a complicated sequence of physiochemical reactions¹⁵ and each aspect of fish culture was affected (survival, growth and reproduction). Temperature, pH and dissolved oxygen changed over time in this experiment but clarity remained nearly constant. T₁ and T₂ had weekly average temperatures of 31.3±1.001 and 31.1±0.661°C, respectively in Fig. 1. The experimental cage temperature was within the appropriate range for culture ponds, which is consistent with the other findings^16-18 but the temperatures of both cages were slightly higher for mrigal culture^4,19.

In T₁ and T₂, the weekly average pH ranged from 7.22-7.85 and 7.27-7.74, respectively, with mean (SD) values of 7.52±0.186 and 7.483±0.149 Fig. 2. The pH values of both T₁ and T₂ agree well with the findings^4-6,9.

The weekly average DO (mg L^–1) was ranged from 5.0-6.6 and 4.7-7.2 mg L^–1 with a mean SD value of 5.71±0.592 and 5.667±0.795 mg L^–1 in T₁ and T₂, respectively in Fig. 3. The level of Dissolved Oxygen (DO) was within the acceptable range in this study in accordance with the other studies^4,7,10.

Growth performance: The growth curve was upper in T₁ compare to T₂ in Fig. 4. T₁ and T₂ achieved average final weights of 69.8±7.3 and 60.8±9.09 g, respectively, at harvest, where the initial weight was 25.4±1.63 g for both treatments (Fig. 5). Shivagami et al.¹¹, who discovered that Mrigal showed developed better in higher feeding rations than lower feeding rations, agreed with this study.

Fig. 1:

Weekly average temperature in both treatments

Fig. 2:

Weekly average pH in both treatments

During the study period, T₁ and T₂ had net weight gains of 44.4 and 35.4 g, respectively in Fig. 5. In T₁ and T₂, weekly weight gain ranged from 3.6-6.4 and 2.8-4.8 g, respectively, with mean SD values of 4.93±0.75 and 3.93±0.72 g in Table 3. In other studies, the weight gain of Mrigal was 62-81²⁰ and 57.06 g²¹ which was close to the present treatment of T₁. Observed in the present study, mean weight gain in percentage was 74.80 and 39.37% in T₁ and T₂ respectively and another finding was 13.64-85.71% in case Indian major carps¹¹. Mean final weight and net weight gain of both T₁ and T₂ based on mean initial weight are given in Fig. 5 which showed the comparison between the growth performance of Mrigal.

The Specific Growth Rate (SGR) of mrigal in T₁ and T₂ were found 1.6±0.71 and 1.38±0.50% respectively in Table 4. The SGR value in both treatments was lower compare to the findings of Biswas et al.²⁰, Zhen-Yu et al.²¹, Desai et al.¹², Abdelghany et al.²², Jena et al.²³, Hossain et al.¹⁷ and Sahu et al.⁴ where they found the SGR of Indian major carps (rohu, catla, mrigal) and common carps usually ranged between 2.0-4.0%.

Fig. 3:

Weekly average dissolved oxygen in both treatments

Fig. 4:

Mean body weight in gram changes of different treatments at a week interval

Fig. 5:

Comparison among mean initial body weight, final body weight and net weight gain between the treatments (T1 and T2)

Fig. 6:

Mean body length changes of different treatments (T1 and T2) at a week interval

Fig. 7:

Weekly length gain comparison between T1 and T2

Fig. 8:

Mean initial body length, final body length and net length gain between the treatments

Fig. 9:

Comparison between FCR values of T1 and T2

Fig. 10:

Comparison between survivability of T1 and T2

T₁ had the highest length (18.2 cm) compare to and T₂ (17 cm) at the harvesting period in Fig. 6. This study showed similarities with the findings of Ayyappan and Jena² and Hossain et al.¹⁷, they showed the length of mrigal had a tendency to increase in higher feeding ratio. Weekly average length gain ranged from 0.2-2.3 and 0.2-2.6 cm with mean SD value of 0.92±0.62 and 0.87±0.75 cm in T₁ and T₂ respectively in Fig. 7. Net length gain for both T₁ and T₂ were found 8.3 and 7.9 cm respectively in Fig. 8. The range of final length was found to vary from 17.5-18.2 cm and 17-18.1 cm respectively in T₁ and T₂ where the average length was 17.9±0.26 and 17.5±0.44 cm at harvest, respectively but the initial length was 9.6±0.83 cm for both treatments (Fig. 8). In the first four weeks, both T₁ and T₂ treatments displayed a greater average weekly weight gain.T₁showed a higher average weekly gain than T₂ similar to the findings with Shivagami et al.¹¹.

Feed conversion ratio: The FCR was lower in T₂ than in T₁, FCR was found 5.78 and 4.62 in T₁ and T₂ respectively in Fig. 9. The FCR of both treatments were higher in comparison with the study of Khan et al.¹³ in which he found that Mrigal showed higher FCR with the use of 4-6% body weight feed. The present study showed dissimilarities with the result of Shivagami et al.¹¹ and Biswas et al.²⁰, where they found FCR value 3.02 and 0.65-0.91 at the different feeding ration of total body weight. FCR values of T₂ treatments showed close to the other studies^24-26 where they found that FCR values of Indian major carps ranged from 1.97-4.91.

Survival rate of C. mrigala: T₁ also had the highest survival rate, while T₂ had the lowest. In T₁ and T₂, survival was found to be 90 and 85%, respectively, while the initial stocking number of fish was 20 in both treatments in Fig. 10. Similar finding (83.9-91.7%) were reported by Sahu et al.⁴ and was dissimilar studies (27.12-48.02)²⁰.

CONCLUSION

In this experiment, fish in treatment 1 (T₁) grew faster than other treatment 2 (T₂), where feed was given at a rate of 10% of the fish's body weight. So, based on the current experimental situation, Mrigal growth is higher in high feeding percentages.

SIGNIFICANCE STATEMENT

This study discovered the growth performance of C. mrigala in cages that can be beneficial for fish culturists. Feed ratio has been improved in the present study which ultimately leads to higher production of this species. This study will help the researchers to uncover the critical areas of the feasibility of mrigal culture in the cage with different feeding rate that many researchers were not able to explore in the past. Thus a new theory on the growth improvement of C. mrigala may be arrived at by the present research.