Zusammenfassung: A telemetric system for automatic positioning of individual fish in the vertical or horizontal plane is described. The position of a transmitter in a fish is computed from the difference in arrival time of the ultrasonic signal to a fixed array of hydrophones. Sources of error in positioning are discussed. In a preliminary study, the resolution of the system in time and space was adequate to monitor the behaviour of adult salmon in a sea cage. At moderate stocking density the salmon was swimming continually in counter-clockwise circles and diel rhythms in swimming speed, depth and path-radius were observed. With only 30 fish in the cage this stereotype behaviour broke down. Few or no visits into the feeding area during some feedings indicated a variable feeding motivation.

Zusammenfassung: A review is made of the literature on the back-calculation of fish body length from marks on scales or other hard parts (otoliths, vertebrae, fin rays, etc.). Though the technique is widely used it does not appear to be well understood. Regression methods are commonly used, apparently in ignorance of the more realistic proportional methods. It is not generally recognized that there are two equally plausible back-calculation hypotheses which can lead to significantly different back-calculated lengths. The Fraser-Lee equation, the most commonly used back-calculated formula, follows neither of these hypotheses but is based on a misuse of linear regression. It is recommended that back-calculation be restricted to procedures following one of the proportional hypotheses; that the difference between lengths calculated using the two hypotheses is a useful measure of the minimum uncertainty in back-calculation lengths; and that more attention be paid to validating back-calculation hypotheses by comparing observed and back-calculated lengths for individual fish. The pattern of heteroscedasticity in body length-scale radius plots is noted as a useful diagnostic in evaluating back-calculation hypothesis.

Zusammenfassung: A new linear regression method is presented for fitting the von Bertalanffy growth function to data on size at age, which is also applicable to tag and recapture data. From tests on simulated data the method shows lower error and bias and more flexibility of action than other commonly used methods.

Zusammenfassung: A method for the multivariate analysis of fish growth in aquaculture is presented. It is derived from a linearized version of the von Bertalanffy growth function (VBGF), which, in its original form, is a bivariate regression termed the Gulland-and-Holt plot. Here, a version in form of a multiple regression equation is presented. The “extended Gulland-and-Holt plot” permits to identify and quantify the key variables controlling fish growth and permits the inclusion of these environmental and treatment variables to explain variance in growth of fish. Von Bertalanffy growth parameters K and L sub( arrow left ) are obtained, which contain the combined environmental effects on fish growth and reflect the range of culture conditions. By computing the index of growth performance ( Phi '), the obtained regression models can be used for growth prediction and decisionmaking in fish farm management and production under a wide range of environmental and management conditions. Recommendations for the design of experiments, preparation of data for analysis and actual analysis procedures are given.

Zusammenfassung: A laboratory study of female G. aculeatus revealed no conclusive evicence of active female mate choice on the basis of male aggression levels. However, highly aggressive males failed in 95% of all choice tests. The less aggressive ´chosen´ males where generally successful again in subsequent trials with the same female, and certain males were consistently successful with different females. Females exhibited an increased readiness to spawn at the end of the reproductive season, although the same males were usually selected again.