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The aim of this thesis has been to investigate the individual decision making abilities of schooling fish in order to understand the composition of fish schools. Do individuals choose particular school-mates, and if so, on what basis are these decisions made? The null hypothesis, that schools are composed of random assortments of individual fish, has been rejected. School membership and structure are profoundly affected by the cognitive abilities and partner choice decisions of fish. Field work carried out in Trinidad and Dorset, UK (on guppies, Poecilia reticulata, and European minnows, Phoxinus phoxinus, respectively) has demonstrated that familiarity does indeed influence choice of schooling partner. Individual guppies under laboratory conditions and in the wild recognise and prefer school-mates with whom they are familiar, and schools of minnows are composed of a significant proportion of individuals which are familiar to one another. Preference for familiar conspecifics develops gradually (over at least 12 days in the case of guppies) and observations of wild guppies shows that this schooling preference is mediated by group size. Tendency to school with familiar fish is strong when group size is small, but declines thereafter, no preference being made as group size increases beyond ~40 individual females. The effect of group size on these partner choice decisions suggests that individual recognition may be possible. Intriguingly, a gender difference in the partner choice decisions of guppy schools in the wild has also been identified. Females spend more time schooling with individuals from their natural schools than males. This has important evolutionary consequences in terms of population differentiation and speciation. It seems, therefore, that schools are by no means composed of a random assortment of individuals. Indeed school structure and membership are profoundly affected by the remarkable discriminatory abilities of individual fish.

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The temporal and spatial variations in the activity of cutthroat trout in a small coastal British Columbia lake (49°19'N, 122°34’W) were examined in order to determine the Impact of activity on the production of fish, and the factors controlling activity. Sonar tracking, diving, netting and tagging, rise observation, stomach content-prey distribution comparision, and echo sounding were used in the Investigation. Average activity levels were at least an order of magnitude below any published values. Energy values were correspondingly low; the maximum estimate of annual energy expenditure in activity (including routine metabolism) was 2330 kCal/kg/yr, which is well below the accepted 'rule' of field metabolism being twice the routine metabolism (3860 kCal/kg/yr). Fish behavioral problems and methodological shortcomings are considered responsible for this result. Activity over 5 min intervals was quite variable. Daily activity peaked during dawn and dusk. The level of activity decreased in late fall and early spring, and there was a shift from the littoral zones during summer. The cutthroat in the lake appear to maintain home ranges-for up to 5 months. Factors affecting activity can be broken into 3 categories: Temperature, light, and oxygen primarily determine the depth zones that are accessible to fish. Substrates such as Potamogeton beds and logs may act to concentrate fish within accessible depth zones; attraction is likely due to the higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity. higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity. / Science, Faculty of / Zoology, Department of / Graduate

Supervisor: N. R. Liley The endogenous and exogenous factors contributing to a diel rhythm of locomotor activity in juvenile sockeye salmon Oncorhynchus nerka (Walbaum) were examined in the laboratory. The basic measure employed in the investigation was spontaneous locomotor activity. High frequency sound (800 kHz) was used as a monitoring technique to collect continuous activity records. Three major areas received attention. First, a description and analysis were provided for the entrained diel activity pattern under three different temperatures (5°, 10°, and 15°C) and three different photoperiods (8L 16D, 12L 12D, and 16L 8D). The combined effects of temperature and photoperiod upon the basic 24 hour response were recorded and analyzed. Juvenile sockeye salmon were nocturnally active immediately after emergence from the gravel. A diurnal activity pattern was gradually acquired during the following 14 days and was maintained for 12 months. Photoperiod was the primary environmental synchronizer for either diurnal or nocturnal activity. The endogenous component of the activity rhythm was examined in constant environmental conditions. Constant light (34.4 lux at 10°C) facilitated the free-running response while constant dark inhibited it. The spontaneous frequency in constant light was 23.30 hours but this could be altered by light intensity or periodic feeding. The final experiments focused upon the relationship between the environmental stimulus (photoperiod) and the physiological sensory mechanisms mediating the entrained response. The eyes were the primary photoreceptors mediating information about the light-dark environment. The entrained activity response disappeared when the retina was not illuminated. When the pineal body was removed or shaded, juvenile sockeye responded with increased activity. Intraperitoneal injections of melatonin (N-acetyl-5-hydroxy-tryptamine) or serotonin (5-hydroxy-tryptamine) selectively altered the activity amplitude in either the light or dark respectively. Juvenile sockeye salmon possess an endogenous circadian activity rhythm which is synchronized by the photoperiodic cycle. The fish are generally light active, except for the period immediately after emergence. However, interactions between daylength and temperature can result in temporary dark active responses. Mediation of the photoperiodic information occurs via the retina, but without transmission by optic nerve pathways. Chemical agents (melatonin and serotonin) produced by the retina and/or pineal might control the activity amplitude in light and dark, thus resulting in the characteristic entrained pattern. / Science, Faculty of / Zoology, Department of / Graduate

The blue gourami, Trichogaster trichopterus, is a small, freshwater tropical fish, native to Southeast Asia. Parental behavior is normally shown only by males after spawning. Females and non-parental males eat small numbers of test eggs which they are given, while parental males retrieve them to their nests. The goal of this thesis was to investigate the factors responsible for the sudden change in behavior from egg-eating to parental care which takes place at the time of spawning. In the initial section, the patterns of parental behavior are described, and quantitative data on the development and maintenance of parental behavior in male fish spawning for the first time are presented. The experimental studies reveal that stimuli from the eggs are an important factor in the induction of parental behavior. Many naive males developed parental behavior within 0.5-2.5 min when given eggs spawned by other fish. This response was dependent upon the number of eggs presented: a large proportion of fish became parental when given 2000-3000 eggs, a smaller proportion did so when given 500-1000 eggs, and none did so when given 100 eggs. However, even 100 eggs evidently affected parental responsiveness because some fish eventually developed complete parental behavior when repeatedly given 100 eggs. These results indicate that eggs can induce parental behavior, not that they do so in the natural spawning situation. However, tests of males spawning with females whose oviducts were plugged indicated that exposure to eggs was an important component in the natural development of parental behavior. Spawning by itself did not induce fish to become parental, but it did reduce the number of eggs necessary for parental behavior to develop. Besides spawning and stimuli from the eggs, androgens also play a role in the development of parental behavior. It was shown that, after spawning, males performed more parental behavior than females, although detailed observations of females revealed that they had some capacity to perform parental behavior. The masculinization of females by means of methyl testosterone implants allowed them to develop parental behavior in response to large numbers of eggs. Whether castration of males eliminated their capacity to perform parental behavior could not be determined with certainty. The presence of young facilitates the maintenance of parental responsiveness to eggs when males with developing broods are compared with males whose broods have been removed. Apparently, physical contact with the young is necessary because males lose their parental responsiveness when their broods are placed in baskets which allow only visual and chemical contact. An important result of this study is the demonstration of the significance of stimulus strength in the induction of parental responsiveness. This factor has not often been taken into consideration in other studies of parental behavior. By varying stimulus strength, repetition of stimuli, and sexual experience, patterns of the induction of parental behavior were found in gouramis which were similar to those observed in other studies on a variety of mammals, birds, and fish. That is, parental behavior developed either almost immediately or gradually with the presentation of young to non-parental fish, or it was shown only if the young were presented during the "sensitive period" after spawning. The finding of such different patterns in a single species as a result of varying the strength of stimuli from the eggs suggested that the motivating effects of eggs and young on parental responsiveness may represent a common pattern underlying the control of parental behavior in a variety of vertebrate species. This possibility and the relationship between hormones and stimuli from the young in the control of parental behavior are discussed in the final chapter. / Science, Faculty of / Zoology, Department of / Graduate

Populations of guppies living in different streams vary in their "behaviour and morphology. Some populations live in fast-flowing streams while others occupy slow-flowing water. I hypothesized that behavioural differences between the populations may represent adaptations to stream velocity. I tested seven predictions based on this hypothesis in two experiments. In Experiment I, I. examined the behaviour of laboratory reared guppies descendant from three natural populations. These guppies were examined at .03, .07, .10, and .20 m/sec stream velocities. Experiment II used wild-caught guppies from four populations. Their courtship behaviour was examined in still water (.00 m/sec) and at .08 m/sec velocity. As predicted, in Experiment I guppies from slow-flowing water showed l) greater cohesion, 2) less aggressive behaviour, and 3) a greater preference for the surface region of stream tanks than fast water fish. Also as predicted, slow water males performed fewer sigmoid displays "but more thrusts and gonopodial swings than fast water guppies. The persistence of these behavioural differences in laboratory raised descendants of isolated populations demonstrates a genetic contribution to the differences. Therefore the differences are presumably the product of natural selection and represent evolutionary adaptations. Experiment I also showed that stream velocity directly affects the performance of courtship behaviour by males. The frequency of sigmoid displays and gonopodial swings decreased markedly as stream velocity increased. As stream velocity increased, fast water males maintained their frequency and duration of sigmoid displays better than slow water males, thus providing evidence for "behavioural adaptation to stream velocity. The higher ratio of sigmoid displays : thrusts exhibited by fast water fish may also represent an adaptation to stream velocity. Stream velocity had no direct effect on group cohesion and aggression in the guppy. However, it directly affected guppy stream depth preference. Slow water fish could not maintain position at the top of the stream in faster-flowing water, whereas fish bred from an intermediate stream velocity population were able to do so. Fast water fish always preferred the bottom of the stream bed. In Experiment II wild-caught fish from fast and slow-flowing streams were tested together in two stream conditions. Again, as predicted, slow water fish performed fewer sigmoid displays but more thrusts and gonopodial swings than fast water fish. Because of the slow velocity used during the experiment, no effect of a fast stream velocity on courtship behaviour was obtained. During the experiment males generally preferred to court females from their own population. These preferences may represent partial isolating mechanisms. I concluded that differences between guppy populations in courtship behaviour and stream depth preference represent adaptations to different stream velocities. Stream velocity is therefore presumed to have been one of several environmental factors that interacted to shape the guppy's present behaviour. / Science, Faculty of / Zoology, Department of / Graduate

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