Relative effects of electro-immobilisation and chemical anaesthesia on in situ post-release behaviour and reproductive success in nesting smallmouth bass (Micropterus dolomieu)

In fisheries science, chemical anaesthesia and electrical immobilisation are often studied in laboratory or aquaculture settings with little focus on post-release behaviours of fish in the wild. We used nest-guarding smallmouth bass (Micropterus dolomieu) as a model species to investigate the relative impacts of chemical anaesthesia, electroanaesthesia with a TENS unit and conductive gloves, and electrostunning on natural behaviours and reproductive success in situ. Electrostunned fish had higher rates of failure to return to nests within 1 h and showed greater behavioural impairment in terms of both pre-release reflex assessments and capacity to resume parental care behaviours compared to other experimental treatments and control groups. The gloves failed to adequately reduce involuntary movements relative to controls but those fish returned to the nest quickly, suggesting potential opportunities for further refinement of methods. However, ultimate nest fate (i.e., abandonment rates) was similar across groups. We discuss the likely drivers for observed treatment effects, or lack thereof, as well as the implications of variation in biotic and abiotic environmental factors to our results. We end with recommendations regarding the use and development of anaesthetic and electro-immobilisation options for research on wild fishes.