WEFTA-Laborvergleichsuntersuchungen zur pH-Bestimmung in Fischerei-Erzeugnissen - Eine gemeinsame Aktion der Western European Fish Technologists' Association

12 samples (6 original samples and 6 diluted samples) were analysed by 14 WEFTA laboratories for their pH values in an inter-laboratory comparison exercise. As a result it can be stated that the majority of participating laboratories could determine the pH values very exactly. The pH values obtained are ranging only little around the calculated mean (less than 0.1 pH unit). It could also be demonstrated that the participating institutes could analyse both, pH values in fishery products and aqueous salt solutions. However, also in this exercise a number of outliers and deviating values have been detected. Therefore it is of utmost importance to calibrate the pH electrodes in regular intervals and to maintain them carefully. Intra-laboratory comparison measurements are recommended to detect weak points.

Preliminary experiments on electrical fishing in fresh watter [i.e. water]

Fishing using electricity is a new technique and is still in the experimental stages in many of the advanced countries. While no published records are available in India, considerable work has been done in Germany, United States, Canada, and United Kingdom. These papers mainly deal with the behavior of the fish in the electrical field, the physiological effects of electrical current on fishes, methods of electrofishing, electric fencing etc. The following experiments on electrical fishing were conducted with a view to studying the distribution of electrical field when an alternating current is passed through two fixed electrodes in fresh water and to study the reaction of different fresh water fishes to the field.

Preliminary observations on the effect of a. c. current on Catla catla and Ophicephalus punctatus

In order to evolve suitable electrical fishing gear for inland waters, preliminary experiments have been conducted to observe effect of a. c. currents on Catla catla at voltages of 30, 90 and 120, pH 7.3 and 8.4, temperature 48°F, 78°F and 105°F, distance between electrodes 25 cm, 50 cm and 75 cm, size range of fish 100 mm, to 235 mm. Apparatus used was a 5 kw; a. c. 60 cycles generator with resistance control. Larger sizes of fish were more prone to electric shock. Higher temperature increases the intensity of the shock, while variation of pH between 7.3 to 8.4 did not materially affect the intensity of the shock. Fishing with a mixed population of Catla catla and Ophicephalus punctatus gave a greater percentage of mortality for the latter.

Preliminary observations on the effect of electrical seine on fish catch

Forty-six experiments were done with the electric seine in 24 tanks with a.c. and interrupted a.c. The source of electrical energy was a 3 Kw a.c. generator of water-cooled diesel engine. A control seining without applying electricity was conducted for every experiment with electric "seine" to have a comparison for the efficiency of electric "seine" over control ones. Electric seine was found to have an increased catch over control seining both in numbers and in weight. Electric seine with two electrodes was found to have better effect over three electrodes. Benthic fishes like Cirrhina mrigala, Notopterus notopterus, Cyprinus carpio, Glassogobius giuris, Ophicephalus sp. and Mystus sp. were found to be more sensitive in electric "seine". Increased catch of small fishes like C. mrigala, N, notopterus and Ophicephalus sp. has been observed in electrical "seine" in addition to larger ones.

Reaction of fishes to the underwater A.C. field

A comparative study on the effect of A.C. field on Puntius ticto, Heteropneustis fossilis and Tilapta mossambica was carried out using a slowly rising field intensity. Well defined reactions appeared in the species of fish with slight specific variations, depending on their orientation in the electrical field, on reaching the field intensity to specific value. These reactions can be distinguished as first reaction, when the fish perceive the surrounding field, jerky swimming when parallel to the current lines (longitudinal oscillotaxis), the static position finally adopted by the fish sooner or latter depending on the potential gradient (transverse oscillotaxis), and a state of muscular rigidity (tetanus). After switching off the current, a hypnotic condition prevailed in the treated fishes before returning to their normal swimming condition. The orientation of fish body in the field had an important bearing on the behaviour reactions and current thresholds necessary for those reactions. Initial reaction, jerky swimming between electrodes and hypnosis after stoppage of current appeared in fishes earlier when the fish body was in parallel to the current lines, whereas fishes responded to transverse oscillotaxis quickly when perpendicular to current lines.

Development of electro-trawl system in marine environment

High voltage pulsed current produced on board a trawler is fed to electrodes distributed along the foot rope of a trawl net through two core TRS cable which builds up a homogeneous electrical field around the net mouth. By comparative fishing tests with the electrified and non-electrified 32 m long wing trawl net, the increase in total catch of shrimps and fishes was found to be 19.8 and 36%, respectively.