Behavioral Responses Of Tilapia (Oreochromis Niloticus) To Acute Stress Monitored By Computer Vision

At present, fish behavior under culture conditions holds important information for aquaculturist. Most of physiological and environmental changes can induce variations in fish behavior. Stress condition such as low dissolved oxygen level, elevated ammonia, abrupt variations in temperature occur frequently in aquaculture systems and severely affect fish mortality. Early detection of stress conditions in fish farming systems can reduce production loss. Acute stress of fish results in severe physiological and behavioral changes compared with fish maintained under normal condition. Plasma parameters changes in catecholamines, corticosteroids and glucose are accepted as physiological indicators of acute stress in fish. Measurements of plasma stress parameters require blood sampling; the sampling course can bring stress from disturbance and influence the value of measurement. The behavioral parameters have the possibility to be measured continuously in-situ by a non-invasive and non-contact approach, and have the potential to be used in the actual productions to predict stress conditions. This project presents the methods of quantifying the behavioral parameters and the skin color of the fish; and the behavioral responses of tilapia under acute hypoxia and high level of unionized ammonia were quantified based on these methods. Details were listed as followed:(1) Quantifying the swimming activity of multi-fish using computer vision Under culture conditions, the fish are in social school and interact on each other. This paper presents a method to calculate the swimming speed of a school of fish in a tank denoted by body length speed that correspond to fish activity using computer vision technique. Frame sequences captured at special time interval were subtracted in pairs after image segmentation and extraction. By labeling components caused by fish movement in difference frame, the projected area caused by the movement of every fish in the capture interval was calculated; this projected area was divided by the projected area of every fish in the later frame to get body length moving distance of each fish, and further obtained the relative body length speed. The average speed of all fish can well respond to the activity of fish school.(2) Quantifying the skin darkness of fish swimming in water using computer visionThe simple but practical method was presented to quantify the darkness of skin color by comparing the lightness with gray scale covered by glass, the skin darkness could be quantified using this method continuously.(3) The behavioral responses of tilapia under acute hypoxia stressThe behavioral parameters and ventilation frequency (VF) alterations of tilapia (Oreochromisniloticus) responded to acute dissolved oxygen (DO) fluctuation during the course of normoxia, DO level declining, maintaining hypoxia (three level of 1.5, 0.8, 0.3 mg l~-1) and subsequent recovery to normoxia were monitored continuously. These parameters of the fish school responded to the DO level acute variations sensitively; had significant changes (P < 0.05) during severe hypoxia course (0.8, 0.3 mg l~-1 level) compared with normoxic condition, but had no significant difference during medium hypoxia course (1.5 mg l~-1level). The VF had no significant difference between two level of severe hypoxia 0.8 mg l~-1 and 0.3 mg l~-1 level during the low DO maintaining course. The activity and distribution parameters had distinguishable difference between the 0.8 mg l~-1 and 0.3 mg l~-1 level. The swimming activity could distinguish different degree of severe hypoxia though had relative large randomicity.(4) The behavioral responses of tilapia to ammonia stressThe behavioral responses of tilapia (Oreochromis niloticus) school to low, moderate and high level of unionized ammonia (UIA) concentration were monitored. The swimming activity and geometrical parameters of the schools such as the location of the center of gravity and the distribution of the fish were calculated continuously. These behavioral parameters of tilapia responded to acute UIA concentration fluctuation caused by the increase of pH sensitively. Under high UIA concentration the activity of fish indicated obvious increase exhibiting an avoidance reaction to high ammonia level; and decreased gradually. Under moderate and high UIA concentration the vertical location of school became erratic and wavered, the school moved up to the water surface and down to the bottom of the aquarium alternately; the school preferred to be more crowded together. Under high UIA level the school stayed at the aquarium bottom finally after several hours' exposure. So the alterations in fish behavior under acute stress can give out the important information useful in predicting the stress.The fish schools under normal conditions swim actively and distribute evenly. The abrupt increasing in swimming activity, acute fluctuation of school, staying at the bottom or accessing to the water surface, obvious decreasing in distribution and darkening in body color are the typical stress signal of the fish to high UIA concentration.(5) The adaptation ability of unstressed and stressed tilapia to the color changes of background. The healthy tilapia can adapt the ambient color in a short period; the darkness of the skin hadsignificant changes (P < 0.05) after 10 second of the color of background changes (from white to black or from black to white). The stressed tilapia loses the ability to adapt the white background immediately.(6) The relationship of the tilapia skin darkness and the stress physiological parameters under...