Comparison of slaughtering Chinese carps (grass carp, bighead, silver carp) and common carp with ordinary method and using electricity and its effects on some indices of the fish's meat

In order to study the slaughtering of carp fish under normal circumstances and using the electricity, and how the two methods effect some criteria regarding the flesh, an experiment was carried out in May 2009 for a period of 5 months in the Aquaculture Research Center, Faculty of Fisheries, Gorgan University of Agricultural Sciences and Natural Resources. 40 fishes by average weight of 1300±30g and average length of 47±11cm were used for this experiment. The fish were put in a tank measuring 60×40×30cm, with anode and cathode electrodes, filled with tap water up to 3/4 of its capacity. The anode and cathode were connected to the power supply, and the threshold stimulation, capacity for pain, and death threshold of the fish caused by alteration of the voltage were registered. It was revealed that the threshold stimulation was the same among the carp fish in reaction to electricity, and no significant differences were observed (P>0.05). Pain threshold was the least in silver carp (6±0.38 volts); however, it was the same for carps, grass carps, and bigheads (7.5±0.49 volts). Also, the death threshold was the same for carp fish and bigheads (18±1.21 volts), while the difference was significant (P<0.05) for grass carps and silver carp (15±1.01 volts). Besides, the pH and TVN of carp flesh were measured over a three-month period in ordinary slaughtering and also using electricity, no significant differences were observed in pH immediately after being slaughtered. While at the end of the second and third months, the difference was significant in some species (P<0.05). Measuring the TVN under the two mentioned conditions demonstrated no considerable changes in slaughtering by electricity until the end of the third month, while ordinary ways of killing showed significant changes (P<0.05). In the way, the bigheads having the minimum and the carps and silver carp had the maximum amount of TVN.