Study On The Relationship Between The Schooling Structure Of Pseudorasbora Parva And Their Vision

The most of fish species have schooling behavior, which is one of keyto study on the relationship of schooling structure with fish behaviorability.The thesis explored the mechanism of schooling, the characteristicsof the structure of fish school andimpacts on their behavior from thefactors such as vision angle.13fishes (Pseudorasbora parva) were selected and kept in theaquarium under controlled conditions, and two remote controlled videocameras were set up to record the positions of fish from up and sidedirections of aquarium simultaneously. Three-dimensional location data ofeach individual can be abstracted from the record in time series. Thecharacteristic parameters data, Nearest Neighbor Distance (NND), VisionAngle (VA), turning angle (TA) as well as individual swimming speed(ISS), have been analyzed for presenting the structure characteristic of fishschool. The results show that NNDs of individuals have kept in a range of0.5-2BL mostly and the Preferred Nearest Neighbor Distances (PNND)are0.6-0.8BL. To avoid a collision, the own fish always keeps theneighbor fish located its visual field in range80o and the variation of turning angle keeps the range from0o to30o (95.83%). Under naturalcondition without any stimulus or disturbance, the fish swims at around0.75BL/s to match the others maintaining in schooling. The results of ourstudy confirm that visual ability plays an important role in the schoolingperformers of Pseudorasbora parva, and the group structure also areaffected by individual states (satiation and hunger).Data showed a rule that the nearest neighbor distance decreases as thevision angle of own fish increases in Pseudorasbora parva school. Toexplore whether other fish schools have the same rules, we selectedHemigrammus bleheri school as a comparative object，which is smaller inbody length,the average body length of individuals was20.3±0.2mm.30individuals selected for observation.The aquarium length, width, heightwere78.0cm,52.0cm,65.0cm respectively, the water depth is5cm. Avideo camera was set up in lab to record the position of fish fromupdirection of aquarium.Two-dimensional location data of each individualcan be abstracted from the record in time series. We selected twoimportant parameters characterizing structure of fish school: nearestneighbor distance and vision angle to explore their relationship inHemigrammus bleheri school. Results show that:1) the vision angles ofPseudorasbora parva and Hemigrammus bleheri are all located within the80o.2) the vision angle range that neighbor fish occupies the own fish view doesn’t increase as the size increases in different species fish schools.3) If NND remains stationary, the maximum vision angle (neighbor fishoccupies the own fish view) and NND have this relationship: A, yis for vision angle (units: degrees), x is for NND (units: BL), A is aconstant and related with body length of individuals.4) When the NND isminimum between the own fish and neighbor fish, schooling isaccomplished and maintained by vision angle.The data shows thatthe distance between fishes is controlled by visionangle. However, does the lateral line have effect on the distances ofindividuals?Two experiments have been designed, Case1: mounting clearglass between opposite two ends in the aquarium as basic standard. Case2:mounting clear glass in the left end, a mirror in opposite end. A videocamera was set up to record the position of fish (Pseudorasbora parva)from side direction of aquarium. The distances from the left glass or rightmirror to individual have been analyzed. The results show that: individualspreferred being closed to the left glass in case1and preferred being closedto the right mirror in case2. Individual preferred to approach right mirrorin case2closer than Individual preferred to approach left glass in case1(the percentage of Individual leaving the left glass is1.46%in case1and9.54%in case2range0-0.5BL). It confirms that vision plays a major rolein the formatting and maintaining fish school and the lateral line does not haveeffect to the distances between fishes in the absence of the olfactoryand vibration and other stimulations.