A NEW WARNING BIOMONITOR USING A WEAKLY ELECTRIC FISH, APTERONOTUS ALBIFRONS (GYMNOTIFORMES), AND THE EFFECT OF TEMPERATURE ON THE BIOELECTRIC RESPONSES

The weak electric wave discharges of the knifefish, Apteronotus albifr ons (gymnotiformes, apteronotidae) are used as a new biomonitor to ass ess water quality deterioration. The principle consists in a real-time analysis of the Electric Organ Discharge frequency and waveform. Thes e two characteristics are naturally stable under standard conditions. Detailed descriptions of the biological sensor and the test apparatus as well as the set-up for recording, processing and analysing the elec tric signals are presented. The relationship between Apteronotus elect ric activity level and temperature of the surrounding water is determi ned. The variation of the water temperature was increased -decreased a nd vice versa. Bioelectric responses are investigated in a 22-32 degre es C temperature range. The A. albifrons rate of electric organ discha rge is temperature dependent rising very significantly with a unit inc rease in water temperature (t greater than or equal to 246.9; df = 108 ; P < 0.001) and decreasing also very significantly with a unit fail i n temperature (t greater than or equal to 310.3; df = 108; P < 0.001). For the set of the individual fish tested, the observed frequency var iations lie between 45.4 and 63.9 Hz/degrees C. Regression coefficient s obtained for downward temperature variations are always bigger than the corresponding coefficients for upward temperature variations. Stud ent t-test comparison of the two types of coefficients reveals a sharp significant difference in 75% of the cases considered (6.167 less tha n or equal to t less than or equal to 18.024; df = 216; P = 0.001). Th e raw data of the A. albifrons electric activity is shown to be charac terized by a phenomenon of hysteresis in the 0.3 to 4.5% range. The Q1 0-values of the discharge rate over the 22-32 degrees C temperature ra nge was found to be 1.6. The observations did not reveal any dependenc e of the A. albifrons signal waveform on the temperature of the surrou nding water. The temperature dependence of the Electric Organ Discharg e frequency imposes the need for a very strict control of the temperat ure variations of the water surrounding the fish in order to ensure th e reliability of using electric fish as indicators.