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Life skills training in hatchery reared fish
thesisposted on 2022-03-29, 00:10 authored by Erin Kydd
Releasing hatchery reared fish into wild habitats has become an increasingly employed strategy for bolstering conservation or commercially important fish stocks. This method, however, has often met with limited success and the hatchery fish suffer from a high rate of mortality upon release. Reasons for this failure are often attributed to the underdeveloped behavioural traits displayed by hatchery reared fish. The rearing of fish in an impoverished hatchery environment may not allow for the development of a full complement of behaviours required to survive the rigours of the natural environment. There is increasing interest in applying remedial steps before the release of hatchery fish to improve the survival rate of the fish post-release. This often involves exposure to novel, live food items and conditioning via predator exposure. To date little work of this nature has been done on Australian species. Despite this, large numbers of fish are released into fisheries in Australia each year. This research examined life skills training, specifically predator recognition, in two species of fish from the troubled Murray-Darling river system, golden Perch (Macquaria ambigua) and trout cod (Maccullochella macquariensis) and one species, Australian bass (Macquaria novemaculeata), from south-eastern Australian coastal river systems. The relative roles of visual and chemical cues in learned predator recognition were investigated, followed by a behavioural interaction experiment with a live predator at liberty in semi-natural conditions.A range of graded responses were observed, however, the intensity of response and preferences for different sensory modalities varied for each species and in different tests. In golden perch (Macquaria ambigua) fingerlings trained using a combination of olfactory cues and conspecific extract (CE) reacted the most intensely. Conditioning using only CE elicited a response that was more generalised than that of the fingerlings conditioned with predator scent and CE, but similar in intensity. In the behavioural predator interaction trial with a predator at liberty in semi-natural conditions, conditioning using a live predator (multiple cues) elicited the greatest response. Fewer approaches toward the predator and an increased use of refuge were observed in fingerlings conditioned with a live predator.When investigating the Australian bass (Macquaria novemaculeata) conditioning fingerlings using only scent cues resulted in an increased use of refuge and a tendency towards looser schooling. Fingerlings conditioned using visual cues or multiple cues recovered faster and exhibited a less intense anti-predator response. Schooling responses were more intense when fingerlings were allowed visual contact with a predator than with the scent of a predator across all treatments. In the behavioural interaction trial with a predator at liberty in semi-natural conditions, combined visual and olfactory cues presented the most intense response, followed by conditioning using only visual cues from the predator. Furthermore, a more distinct difference between treatments was seen in measures of activity rather than of refuge use. Results suggest a stronger partiality to visual cues in this species. Finally, the results of the trout cod (Maccullochella macquariensis) demonstrated the use of multiple cues during conditioning increased the range of responses seen in the fingerlings including predator inspection. Results from the behavioural interaction trial with a predator at liberty in semi-natural conditions also show a stronger response to conditioning using a combination of visual and olfactory cues, or olfactory cues alone. The results presented here suggest the use of chemical and visual cues to enhance predator recognition may be successful in modifying the behaviour of hatchery reared fish in all three study species, however, these appear to be both context specific and species specific. The use of tailored life skills training programs in these species could potentially improve post-release survival of hatchery reared juveniles.