Preliminary experiences in the development of bluefin tuna Thunnusthynnus (L., 1758) electroslaughtering techniques in rearing cages

摘要

With the increasing economic importance of bluefin tuna (BFT) (Thunnus thynnus) and the need to supply a market on demand, the number of tuna farms is growing. This paper presents the results achieved in the improvement of tuna meat quality when slaughter on tuna farms was carried out using electrostunning and electrofishing techniques which have been used with small freshwater fishes for a century. This method was chosen because it offers a number of advantages: selection capacity and low stress level for tuna. Due to the large difference between freshwater and seawater conductivity, the discharge is applied using a harpoon rather than by generating an electric field. This study compares the meat quality obtained using different waveforms. Meat quality is assessed on the basis of two parameters: meat colour score and spinal injuries score. The waveforms tested were: constant current, high frequency pulsed direct current, complex pulse system, low frequency pulsed direct current, regulated alternating current and mixed signal. Only some of these had been tested in freshwater. According to the tests reported, only one of all the waveforms used in freshwater electrostunning was effective in seawater - that is the low frequency pulsed direct current, which caused moderate injuries. However, other waveforms which had not been tested in freshwater proved more effective. The best results were achieved with a mixed pulsed direct current and alternating current signal, which produced a reasonable quality level with moderate voltage and current and therefore has a low power requirement.