The Electrosensory Behavior And Response Properties In Dorsal Octavolateral Nucleus (don) Of Sturgeon

The electrosense is the ancestral vertebrate sense and present in many aquatic animals and is used in prey detection, avoidance and mating. The electrosense is divided into primitive passive electrosense and new active electrosense, and their electroreceptor are ampullary and tuberous. The sturgeon and paddlefish in the order Acipenseriformes are chondrostean and one of the primitive fish and typical passive electrosensory fish in present. Their electroreceptors distributed in head and rostrum which carry the electrical information to first special nucleus. The research on the electroreceptor, behavior and information processing in brain were well documented in Paddlefish, Polyodon spathula. However, it is unknown in sturgeon. The study investigated the electrosensory function in Siberian Sturgeon, Acipenser baerii by experimental behavior and the response properties in electrosensory neuron in White Sturgeon, Acipenser transmontanus. The significance of this study was to accumulating the information in evolution of electrosense and to provide the basic data on protection and aquaculture in sturgeon. The major results are the following:1. The response of Siberian Sturgeon, Acipenser baerii to corrosion electric fields from meal objectThe responses of Siberian Sturgeon, Acipenser baerii to aluminum, T-aluminum and plastic rods were investigated and the corrosion fields from metal rod were measured as well. The behavior experiment was conducted in darkness with 10 fish by IR-video recording. The results showed that the electric fields from aluminum rod were 1-3Hz with 90μV (2.5cm), 70μV (2.0cm) and 50μV (1.5cm) peak to peak. There was no or less electric field from T-aluminum rod. The behavior results showed that the fish food foraged and food striked at the rods. There was significant difference between aluminum and other rods (P<0.01). In food striking, aluminum and T-aluminum rod showed significantly difference with plastic rod (P<0.01), and there was NS between aluminum and T-aluminum. In food searching, there was NS among three kinds of rods (P>0.01). Gamma coefficient showed there was significant negative relative to the diameter of aluminum rods in food striking (G=-0.278, P=0.003), positive relative in T-aluminum rods (G=0.559, P=0), no relative in plastic rods (P=0.777). And there was significant positive relative to diameter of aluminum rods in food searching (G=0.612, P=0), no relative in T-aluminum and plastic rods (P=0.445; P=0.08). In the preference of degree, the aluminum had the max preference with value of 4.71; in T-aluminum the preference was 2.23; but there was no or least preference to plastic with value closing to zero. These results suggested that the sturgeon could feed with electrosense, and they also use olfaction in feeding without electric cues. It had also implications that the artificial electric field would influence the sturgeon in feeding and reproducing.2. The bioelectric field of Mosquito fish, Gambusia Affinis and the response of Siberian sturgeonIn this study, the bioelectric field of Mosquito fish (Gambusia Affinis Baird & Girard), a kind of living prey of sturgeon, was investigated in single fish, pair of same direction and pair of opposite direction. And the behavior response of Siberian sturgeon to the Mosquito fish closed in the gelatin chamber and odor of pellets from gelatin was analyzed. The bioelectric field of single fish presented as direct current electric field of dipole type, with relative potential up to -24±2.4μV on head and 21±1.6μV on tail. And the alternating current electric field was modulated with 4.2±0.8μV at 1-3 Hz which corresponded with the respiratory rhythm. In two fish with same and opposite direction, the direct current electric fields were larger than the single fish (P<0.05), but the alternating current electric field was larger than the single fish measured in same direction (P<0.01), and was smaller than single fish in opposite direction (P<0.001). It suggested that the schooling fish could change the alternating current respiratory potential through the different directions. This phenomenon was unbeneficial for the feeding of passive electrosensory fish. The behavior results showed that sturgeon food striked at bioelectric field from Mosquito fish and odor from pellet solution and there was no significant difference between two gelatin blocks (P<0.001). It further suggested the electrosense and olfaction was used by sturgeon in feeding.3. The response properties of DON, dorsal octavolateral nucleus to dipolar electric fields in White Sturgeon, Acipenser transmontanusIn this study, the response properties of DON, dorsal octavolateral nucleus to different amplitudes and different frequencies of dipole fields was investigated by electrophysiological method in White Sturgeon, Acipenser transmontanus and the two dipoles with different direction were used to determine the selectivity in DON units. The results showed the DON units modulated the spontaneous activity and phase locked to the sinusoidal electric fields. With different amplitudes at 5Hz the relative discharge rate and the degree of phase-locking increased with amplitude ranging from 25 to100μV/cm in DON; with different frequencies at 25μV/cm the relative discharge rate changed a little, but the phase-locking increased with frequencies ranging from 1 to 5Hz. There was apparent selectivity in dipolar direction expressed as opposite polarity of phase-locking. With further analyzing, the DON units could be catalogue into two types with low spontaneous activity (rate<10Hz) and high spontaneous activity (rate>10Hz) and processed the information with rate coding and phase coding. In rate coding, the spontaneous activity of DON units acted as carrier frequency. And the character of phase coding was phase locking. The units with low spontaneous activity had strong phase-locking and the units with high spontaneous activity had high relative discharge rate. DON units preferred to use phase coding responding to electric fields with low intensity, and rate coding with high intensity. These response properties of DON units matched the biological function in feeding and reproducing.