Estimation of length-weight relationship and condition factor of spotted snakehead Channa punctata (Bloch) under different feeding regimes

Comparative study was conducted to observe the efficacy of different feeding regimes on growth of Channa punctata. Six iso- proteinous diets were prepared by using different agro industrial by-products. Maximum weight gain was recorded with diet having 66.75% rice bran, 11.50% mustard cake, 23.0% groundnut cake, 5% molasses, 1.5% vitamin-mineral mixture and 0.5% salt with specific growth rate of 0.408. The experimental fish recorded the value of exponent ‘b’ in the range of 2.7675 to 4.3922. The condition factor ‘K’ of all experimental fish was above 1.0 (1.094- 1.235) indicating robustness or well being of experimented fish.


Introduction
The spotted snakehead, Channa punctata (Bloch) is well known for its taste, high nutritive value and medicinal qualities (Haniffa et al. 2004) and is recommended as a diet during convalescence (Chakraborty 2006). It is distributed throughout the South-East Asian countries and has been identified as a potential species for rearing in paddy fields, derelict and swampy water as it is an air breathing and hardy fish. It has high market value because of the flavour and availability throughout the year. The fish is suitable for both monoculture and polyculture. Good deal of work has been carried out on different aspects of survival and growth, length-weight relationship, condition factor of C. punctata in India and abroad (Victor and Akpocha 1992;Dutta 1994;Bias et al. 1994;Alam and Parween 2001;Islam et al. 2004;Kumar et al. 2013). However, limited studies are conducted on growth and culture potentiality of this species. Therefore the present work has been carried out to study the efficacy of different formulated diets on survival and growth rate of C. punctata.

Experimental setup
The study was conducted at the Fish Farm of College of Fisheries, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana (Punjab), India (30.54°N latitude, 75.48°E longitude and an altitude of 247 m above mean sea level). The growth of fish was assessed w.r.t. different formulated diets over a period of 90 days. The studies were conducted in PVC cistern (1.50 m×1.0 m ×1.0 m) in triplicate. 5 cm soil bed was provided in each cistern and water depth was maintained 50 cm throughout the study period. Each cistern was stocked with 25 fingerlings (average length = 11.645± 0.3145 cm, average wt. = 11.961 ± 0.1348 g) of Channa punctata collected from wild source.

Formulated diets
Six isonitrogenous diets (33.19 -35.23% crude protein on dry weight basis) i.e. D 1 , D 2 , D 3 , D 4 , D 5 and D 6 were formulated using agroindustrial byproducts like rice bran, mustard cake, fish meal, ground nut cake and soybean meal (Tables 1 and 2). For preparation of diets, all feed ingredients (dry) were first grounded to a small particle size in a laboratory electric grinder and sieved through an approximately 250 μm sieve. Ingredients were thoroughly mixed in a food mixer for 15 minutes. Enough water was slowly added to make stiff dough.
The wet mixture was steamed for 5 minutes and the diets were produced in a noodle-like shape of 2.0 mm in diameter using a meat grinder. The pelleted diets were dried overnight at 55°C afterwards were broken up and sieved into appropriate pellet sizes. Proximate composition of feed ingredients and formulated diets was determined following the standard methods of AOAC (2005).

Feeding of fish
Fish were fed with formulated diets @ 2% of body weight at 10 am daily. The feed quantity was regulated based on the fortnightly sampling of 10 fingerlings from each treatment.

Water analysis
Throughout the study period physico-chemical parameters of water samples including water temperature, pH, dissolved oxygen, total alkalinity, hardness, NH 3 -N, NO 3 -N, NO 2 -N and PO 4 -P were measured following standard methods (APHA 2005).

Growth analysis
Fish were measured in terms of weight gain and increase in length. Total length (TL) was measured to the nearest 0.1 mm using a 30 cm ruler as the distance from the tip of the anterior most part of the body to the tip of the caudal fin. Analytical balances with precision of 0.01 g were used to record body wet weight (BW).
Following growth analysis were calculated Where, weight recorded in gram. ii. Length-weight relationship: The length-weight (log-transformed) relationships were determined by linear regression analysis and scatter diagrams of length and weight were plotted. The length-weight relationship of the experimented fish is worked out as per cube law given by Le Cren (1951).
Where, W=Weight of fish (g), L is observed total length (cm), 'a' is the regression intercept and 'b' is the regression slope. The logarithmic transformation of the above formula is- iii. Fulton's condition factor (K): Fulton's condition factor (K) was calculated according to Htun-Han (1978) equation as per formula given below: Where, W=weight of fish (g), L=Length of fish (cm).

Statistical analysis
The analysis of covariance was performed to determine variation in 'b' values for each species following method of Snedecor and Cochran (1967). The statistical significance

Results and discussion
Lower dissolved oxygen content of water did not create any adverse effect on survival and growth of fish because of the accessory respiratory organ present in Channa punctata (Table 3). There were no significant differences in water quality parameters viz. temperature, pH, dissolved oxygen, total alkalinity, Hardness, NH 3 -N, NO 3 -N, NO 2 -N and PO 4 -P observed among different treatments and all these parameters (except dissolved oxygen content) were within the range as suggested by Boyd and Pillai (1984); Rowland (1986) and Boyd and Tucker (1998) but significant variation was observed within a single treatments in time series data of different parameters. 100% survival of fish was observed in all treatments. Specific growth rate was observed maximum in D 3 followed by D 4 , D 5 , D 2, D 6 and D 1, respectively (Table 4). Initial and final average weight (g), Lengthweight rela-co-efficient 'b' and logarithmic relationship between length and weight with regression equation is given in Tables 5, 4 and Figure 1. In the present study final 'b' varied between 2.7675 to 4.3922. Growth is said to be positive allometric when the weight of an organism increases more than length (b>3) and negative allometric when length increases more than weight (b<3) (Wootton 1992). When TL was regressed with BW, the slope value was significantly lower than critical isometric value i.e. 3, in treatment D 1 and D 6 indicating negative algometric growth; thus species become slender as it increases in length (Pauly 1984) where as b value was higher than 3 in D 2 , D 3 , D 4 and D 5 treatment, indicating the species becomes heavier for its weight, as it grows longer (Thakur and Das 1974). The results of the present study is in conformity with the views of Le Cren (1951) and Chauhan (1987) that a fish normally does not retain the same shape or body outline throughout their lifespan and specific gravity of tissue may not remain constant, the actual relationship may depart significantly from the cube law. Negative allometric growth pattern have been reported in C. punctata by Haniffa et al. (2006) and Ali et al. (2002). Negative allometric growth has also been reported in C. maurulius (Dua and Kumar 2006;Rathod et al. 2011) and in C. Striatus (Khan et al. 2011). Variation in slope may be attributed to sample size variation, life stages and environmental factors (Kleanthids et al. 1999). The higher slope  of C. punctata in D 2 , D 3 , D 4 and D 5 reflect the faster growth compared to D 1 and D 6 in the present study. The condition factor (K) of a fish reflects physical and biological circumstances and fluctuations by interaction among feeding conditions, parasitic infections and physiological factors (Le Cren 1951). This also indicates the changes in food reserves and therefore an indicator of the general fish condition. Moreover, body condition provides an alternative to the expensive in vitro proximate analyses of tissues (Sutton et al. 2000). Therefore, information on condition factor can be vital to culture system management because they provide the producer with information of the specific condition under which organisms are developing (Araneda et al. 2008). The values of condition factor 'K' recorded in the present study are 1.094, 1.116, 1.210,1.171, 1.334 and 1.235 in D 1 , D 2 , D 3 , D 4, D 5 and D 6 , respectively. Condition factor of greater than one showed the well being of fishes fed with different experimental diets. The values of 'K' in D 2 , D 3 , D 4, D 5 and D 6 were higher than D 1 , suggesting that fish fed with diet containing different experimental diets (Table 5) were much more robust than the fish fed with diet in D 1 . The results are conformity with the study of Chandra and  Jhan (2010) who recorded the K value of Channa punctata in the range of 1.05 -1.89. The co-efficient of determination (r 2 ) values explained the proper fit of the model for growth. In the present study, lowest value of r 2 of Channa punctata were recorded as 0.622 (62% variability) in D 1 and highest recorded as 0.892 (89% variability) in D 4 (Table 4) indicating more than 62% variability by the model and good fitness.

Conclusions
In present study, growth rate, condition factor and coefficient of determination value recorded on acclimatization of wild stock of C. punctata under experimental condition indicated a favourable response of the fish to the ecological transition from the wild habitat to the experimental environment. The appreciable growth rate exhibited by the fish during rearing period indicated that the prevailing environmental conditions were within the tolerance range for the species. The findings of the present study support that the species can be cultured in large scale as food fish to meet the nutritional demand.