An investigation of the effects of enrichment of fish pond on growth performance of Catla catla, Labeo rohita and Cyprinus carpio in Thatta District was carried out in newly made earthen ponds with the dimension of 15m x 8m x 1.5m (length x width x depth) located at the Chilya Fish Hatchery, Chilya, Thatta (Sindh). The experiment was conducted with three replications for each treatment. After a routine preliminary preparation, these ponds were fertilized with two organic manures (Poultry manure and Cowdung) and two inorganic fertilizers (Nitrophos and Urea). The fertilization of ponds was done monthly at the rate of 0.17 gm N/ l00 gm of Poultry manure, 0.2 gm N/100 gm of Cowdung, 0.15 gm N/100 gm of Nitrophos and 0.2 gm N/100 gm of Urea with respect to wet body weight of experimental fish for a period of one year.
The neonates of Catla catla, Labeo rohita and Cyprinus carpio were introduced in freshly fertilized ponds obtained from government operated fish hatchery Chilya, located near by to the experimental ponds. The ponds were stocked separately with the stocking density of a total of 64 neonates per pond Among 64 neonates, 16 were Catla catla, 38 were Labeo rohita and 10 were Cyprinus carpio.
The cultured fish stock was sampled randomly from each of the pond understudy separately after every replication. The morphometric characteristics of fish were measured to observe their growth performance under different treatments and. then the captured fish were released back into their respective ponds.
Initially, mean weight of Catla catla was 68.53gm, Labeo rohita 88.27gm and Cyprinus carpio 88.20gm respond extremely well under the enrichment of Cow.dung added at the rate of 0.2 gm N/l00 gm of wet body weight comparing to other three fertilizers. The total fish production under this treatment was 51.96 kg/ year in the experimental pond with 1180.67 kg/acre. Among the tested fishes, Labeo rohita grew the best. The growth rate/day for Labeo rohita was 95.02 gm while the individual growth/day was 2.50 gm. Moreover, in the percent contribution of total fish production, again Labeo rohita contributed significantly i.e. 66.74%. The performance of Catla catla was recorded next to Labeo rohita, which grew 32.96 gm/day with the individual growth rate of 2.06 gm/day. The percent contribution in total fish production was 23.15% followed by Cyprinus carpio, which grew 14.37 gm/day with an average of 1.43 gm/day individual growth rate with only 10.09% contribution. In Cowdung enrichment, over all growth rates of three carps remained maximum i.e. 142.36 gm/day. The nutrients released by Cowdung, standing planktonic biomass and temperature were the variables, which promote the growth performance of carps significantly ascompared to the rest of the fertilizers.
The length-weight relationships of three carps under the enrichment of four different kinds of fertilizers followed almost isometric growth pattern except for Catla catla under Urea, Labeo rohita under Urea and Cyprinus carpio under Cowdung and Urea treatments. The coefficient of condition (K) of all the three carps with respect to body size was coincided by the suitable environmental conditions as the enrichment promoted algal growth in all the ponds niches. The coefficient of conditions for Labeo rohita and Cyprinus carpio were significantly affected by the pond enrichments.
The nitrogen incorporation efficiency (NIE) of three tested carps revealed that nitrogen released from the used fertilizers have significant effects for increasing fish yield. The over all nitrogen incorporation efficiency was recorded maximum in Urea treatment (1.33%) followed by Nitrophos (1.07%), Cowdung (0.99%) and Poultry manure (0.96%). The relationship between nitrogen incorporation efficiency and increase fish yield was (0.99% and 4432.58 gm) remained best in Cowdung treated pond due to better release and composition of nutrients along with environmental suitability.
Temperature was one of the important variables found during the study that trigger ecological steps in ponds. It was observed that significant impact on nitrogen incorporation efficiency but highly significant impact was noted on fish yield through out the study. The amount of nitrogen released from applied fertilizers was the key factor to increase the fish yield. Among the four fertilizers used, Urea showed relatively less yield, as it only augment nitrogen deficiency.
The rate of increase fish yield was corresponded with the enrichments response in the form of planktonic biomass. Significantly higher planktonic biomass (3844 gm/m3) was manufactured against which higher fish yield (300.46 gm/m3) was obtained under the enrichment of Cowdung with 7.55% conversion efficiency of planktonic biomass followed by Poultry manure.
Like wise any agriculture, yields will not be enough unless the conditions of soil are satisfactory. Keeping this in view, the water used for cultivation of fish enriched with four different kinds of fertilizers. These fertilizers supply adequate levels of nutrients necessary for production of primary producers and ultimately for the fish. During the whole study period, the physico-chemical properties of water were fluctuated and affect the production of planktonic biomass and fish. All the physical parameters (temperature, light penetration, pH, total dissolved solids and total suspended solids) were significantly affected on planktonic biomass in all the treated ponds except in Nitrophos treated pond, which show 64.1 % dependence. While some selected chemical parameters (dissolved oxygen, total alkalinity, carbonates, bicarbonates, calcium, magnesium, potassium and chlorides) have pronounced effects on planktonic biomass production among all the used fertilizers.
All the said physical and chemical parameters of water were highly significant in case of fish yields showing that the application of fertilizers to improve water quality was successfully done and provide suitable ecological conditions for better growth of experimental fishes. This suitability was also confirmed by the survival rate, as there was no mortality occurred through out the study period.
The coefficient of correlation among all the physico-chemical parameters under Poultry manure and Cowdung were significant while other two inorganic fertilizers (Nitrophos and Urea) were non-significant due to low biodegradation and non-balanced nutrient profile.
The pond enrichment was used to maximize the pond production. In order to obtain the maximum production, a balance between cost and benefits must exist. To economize the pond enrichment, the results transformed into one acre fish production. The output from Cowdung was the best with the ratio between cost and benefits of I: 1.88 when the total cost was Rs. 37,602.45 and total income was Rs. 70,840.20. The cost efficiency of Poultry manure was ranked second with cost and benefit ratio of 1: 1.14 when the total cost was Rs. 35,864.43 and total income was Rs. 53,072.40. As compared to this, Nitrophos ranked third with cost efficiency ratio of 1: 1.13 when total cost was Rs. 43,108.00 and the income was Rs. 49,062.00. The income was in deficit with the cost benefit ratio of 1 :0.85 in case of Urea, when the total cost was Rs. 37,765.38 and income was only Rs. 32,190.00. These results concluded that using ecological and economical sustainability as the criteria, optimum dose of fertilizers for fish was evident from the cost benefit efficiency showing maximum net revenue.