Water quality parameter
The water quality parameters in experimental tanks during the culture period were recorded fortnightly. The range values of different parameters of the water including water temperature (23.6-29.9°C), dissolved oxygen (5.02-10.13 mg/l), pH (5.5-7.68), alkalinity (40-122 mg/l), hardness (34-94 mg/l), total ammonia (0.14-0.46 mg/l), phosphate (0.01-0.1 mg/l) and nitrite (0.005-0.26 mg/l) were in acceptable range without indicating any remarkable pattern during the whole duration of the experiment.
Growth performance
The initial mean weight of
O. belangeri for different treatments was ranging between 12.43 to 13.36 g, which grown to 19.81 to 23.55 g in the final mean weight. The highest mean weight was found in T
2 group (23.55±0.08 g) fed 25% protein diet which was significantly (
P<0.05) different from other treatments and the least value (19.81±0.32 g) was found in 45% protein diet (T
6). The specific growth rate (%/day) was found highest in T
2 (1.47±0.04) group. The highest body weight gain (BWG) was also found in T
2 (80.84±3.44 g) group (Table 4).
The dietary protein is considered as vital in the nutrition and feeding of fish and thereby adequate supply of dietary protein is essential for better growth and survival
(Shang et al., 2018; Ramesh et al., 2017; Lovell, 1989). Many workers have studied the dietary protein requirement of different aquaculture fish species
(Surjobala et al., 2019; Ramesh et al., 2017; Paul and Giri, 2015;
Siddiqui and Khan, 2009;
Santiago and Reyes 1991) and they have found that the dietary protein requirement for fishes differs from species to species. This is mainly because of their feeding habit, size of fish and water temperature of the particular environment.
Arnason et al., (2010) and
NRC (2011) reported that with the increase in size and age of fish, the protein requirements of fish decreases. Most important aspects in fish farming are feed and nutrition because feed itself represent more than 60 per cent of the production cost
(Han et al., 2018; Li and Wang, 2004). So, it is well known that protein is the most important and expensive item of the fish feed that should be given in adequate amounts to support good growth with minimal cost
(Han et al., 2018; Zehra and Khan, 2011).
In the tropical region, fish require temperature of 25-32°C for the best growth and all other metabolic activities (
Solomon and Ezigbo, 2010) of fish. The difference in temperature affects the feeding intensity of fish and thereby growth rate of fish, which has been reported from the study undertaken in aquarium system
(Zenebe et al., 2003). The present outcome is in agreement with the findings of
Bahnasawy et al., (2009), who reported that the weight gain of fish increased significantly with increasing dietary protein level from 17% to 30% in comparison to non-significant increase with the diet of 35% crude protein in Nile tilapia. Optimum protein requirement was found to be 30% for bighead carp (
Aristichthys nobilis) (
Santiago and Reyes 1991), 25% for
O. belangeri fingerling
(Surjobala et al., 2019), 45.1% for fry of
O. belangeri (Ramesh et al., 2017), 41.4% for pre-adult gilbel carp (2017).
Martinez-Palacios et al., (2007) and
Lee and Kim (2009) explained that specific growth rate is an excellent indicator of protein quality and decreases as fish increase in size.
Li et al., (2000) observed a significant growth response in channel catfish (
Ictalurus punctatus) when the experiment was conducted using different protein rich artificial diet and is in agreement with the present findings.
Ramaswamy et al., (2013), Ye et al., (2017), Surjobala et al., (2019) reported that the decrease in growth rate of fish when the protein levels reach the optimum requirement, which might be because of the fact that the fish body cannot utilize the dietary protein after reaching the optimum protein level as required by the fish.
Studies conducted on stunted fingerlings of
Chirrhinus mrigala by
Swamy (2004) and in another study conducted on stunted fingerlings of
L. rohita by
Kumar et al., (2011) and both the studies reported highest specific growth at about 25% protein diets, which is similar to the findings of the present experiment. The decrease in growth rate of juvenile of
O. belangeri with increasing level of protein above the satisfactory level in the present study is similar to those reported for
Catla catla (Ramaswamy et al., 2013; Dars et al., 2010). The growth rate of the fish significantly decreases beyond the requirement level of protein for fish, indicating that 25% protein diet satisfied the protein requirement of the fish and is considered optimum for attained maximum growth and efficient protein conversion efficiency. Each fish has a certain protein limit after which excess protein level could not be utilized efficiently after achieving a certain size and age. Decreasing the dietary protein requirements with increasing fish size and age were also reported by
Arnason et al., (2010), NRC (2011).
Yield parameters
Between different treatments, significant differences (
P<0.05) were recorded for the final biomass and net gain biomass. The final biomass recorded was highest for T
2 (356±1.52 g) and the least value was found in T
6 (284±0.98 g) group. Similarly, T
2 recorded significantly highest net gain biomass (160.5±5.68 g), compared to other treatment groups (Table 5).
Dauda et al., (2019) reported that the excess protein levels in the feed increased the amino acid catabolism in fish body and caused higher ammonia excretion and accumulation of nitrogen waste in to the culture system. It is also evident that insufficient protein in the diet leads to poor growth in many fishes (
Ahmed and Maqbool, 2017;
Kim and Lee 2005) because of insufficient amino acids supply to maintain the body composition (
Halver and Hardy, 2002). Similarly, the present experimental outcome is in an agreement with the above said statement in
O. belangeri.
Feed utilization parameters
No significant (
P>0.05) differences for feed utilization parameters were recorded among different treatment groups. However, the lowest FCR value (2.18±0.01) was measured in T
2 group. The highest value of FCE (45.83±1.16%) was observed in T
2 group, but without any significant variations among treatments. The apparent PER value was highest in T
2 (0.18±0.01) group fed 25% protein diet. Similarly, the highest PCE (28.24±2.01%) was also recorded for T
2 group (Table 6).
Osteobrama belangeri is an omnivorous fish prefers to consume macrophytes and inclusion of high protein in diet might have problem in feed utilization and leading to poor growth. The highest specific growth rate was found in T
2 group (1.47±0.04) and lowest in T
6 (0.98±0.06). The feed utilization parameters showed no significant (
P>0.05) difference among treatments. Feed conversion ratio (FCR) was found decreased with increasing maximum satisfactory dietary protein level and similar trend was observed by
Ramesh et al., 2017; Ahmed and Maqbool, 2017). So, comparatively lowest FCR was recorded in T
2 (2.18±0.01) group fed with 25% protein diet. Also, relatively higher apparent protein efficiency ratio (PER) was observed in T
2 (0.18±0.01).
Li et al., (2006) reported that 24% and 36% protein diet provided the same growth and feed conversion efficiency and recommended that 28% protein containing diet would be optimum for the growth of fingerlings of
Ictalurus punctatus. Our findings with respect to growth, feed conversion ratio and protein efficiency ratio is also in agreement with the outcome of
Ahmed and Maqbool (2017) and
Aminikhoei et al., (2015), who have worked on
Cyprinus carpio Var. Specularis and Juvenile Israeli carp
C. carpio, respectively.
Proximate composition of the experimental fish
The proximate composition of
O. belangeri did not show significant variations (
P>0.05) among treatments but highest crude protein value was found in T
2 (56.84±0.47) group. The highest ash (%) content was recorded in T
6 (90.1±0.13). The highest lipid level (%) was found in T
2 (34.38±0.31) group. The highest fiber content was found in T
5 (0.39±0.03%) and lowest was in T
1 (0.27 ± 0.04%) group. The highest nitrogen free extract was recorded in T
5 (6.11 ± 0.18%) and lowest in T
2 (26.1±0.35%) group (Table 7).
No significant differences (
P>0.05) in the proximate compositions of the fishes were found among the different treatments. But, minor numerical variations were observed in mean values of moisture, ash, crude protein, crude lipids, crude fiber and NFE. Lipid level of
O. belangeri fish in all the treatments found to be markedly higher as compared to other carp fish. The lipid level range (3.28-3.44%) and thus present result indicated that
O. belangeri is a fatty fish. The carcass protein and lipid contents were found to increase with increasing level of optimum protein and lipid incorporation in the diet. Our results on proximate composition of juvenile
O. belangeri are also in conformity and show similar trend with the findings of
Ramesh et al., (2017), who conducted their study on fry of
O. belangeri. The protein level of 25% in the diet gives the optimum overall performance which includes growth, feed utilization and carcass composition using semi purified diet in laboratory condition.
