INVESTIGATIONS INTO THE FORMATION OF RAINBOW TROUT (ONCORHYNCHUS MYKISS) SOCIAL HIERARCHIES AND POSSIBLE HIERARCHICAL DISRUPTION BY AN ENVIRONMENTAL PERTURBATION

Abstract

<p>Salmonids, such as rainbow trout, form social hierarchies, consisting of dominant and subordinate individuals, when in groups in environments with limiting resources, such as space or food. There were two main objectives for this thesis: to investigate the physiological consequences of being in a social hierarchy as well as to investigate whether grouped social status or individual behaviour most accurately recorded physiological data for a hierarchy and secondly, to investigate the behavioural and physiological changes of groups of rainbow trout exposed to ammonia concentrations which are above chronic protected guidelines.</p> <p>To create social hierarchies, groups of four fish were fed by a new method using a darkened feeding container, twice daily (morning and evening) for eight days. Each morning feeding was videotaped in order to record aggressive behaviour. Each aggressive act was scored, allowing for fish to be assigned a social status. For ammonia exposures, groups of fish were exposed to either 700, 1200 and 1500 µM total ammonia (or 2.97, 5.10, 6.37 µM NH3, respectively) 24 hours before first feeding and these concentrations were maintained throughout the experiment. On day 5 and day 10, physiological parameters were taken in fish fasted for 24-h in control and 700 µM total ammonia exposed hierarchies.</p> <p>Social hierarchies were created in all ammonia-free and 700 µM total ammonia groups, with no hierarchies formed in 1200 and 1500 µM total ammonia groups. In M.Sc. Thesis – Josias (Si) Grobler McMaster University – Department of Biology iv ammonia-free hierarchies, one fish would become dominant, while the three subordinate individuals would each assume a stable social rank and display similar physiology which was different from the dominant fish.</p> <p>Fish from the 700 µM total ammonia group showed reductions in various physiological parameters during period 1, however, these fish displayed similar values as what was reported in ammonia-free hierarchies during period 2. This suggests biochemical or physiological changes occurring in these fish in order to acclimate to the high ammonia environment</p>