Capture and discard practises associated with an ornamental fishery affect the metabolic rate and aerobic capacity of three-striped dwarf cichlids Apistogramma trifasciata.

Fishing causes direct removal of individuals from wild populations but can also cause a physiological disturbance in fish that are released or discarded after capture. While sublethal physiological effects of fish capture have been well studied in commercial and recreational fisheries, this issue has been overlooked for the ornamental fish trade, where it is common to capture fish from the wild and discard non-target species. We examined metabolic responses to capture and discard procedures in the three-striped dwarf cichlid Apistogramma trifasciata, a popular Amazonian aquarium species that nonetheless may be discarded when not a target species. Individuals (n = 34) were tagged and exposed to each of four treatments designed to simulate procedures during the capture and discard process: 1) a non-handling control; 2) netting; 3) netting +30 seconds of air exposure; and 4) netting +60 seconds of air exposure. Metabolic rates were estimated using intermittent-flow respirometry, immediately following each treatment then throughout recovery overnight. Increasing amounts of netting and air exposure caused an acute increase in oxygen uptake and decrease in available aerobic scope. In general, recovery occurred quickly, with rapid decreases in oxygen uptake within the first 30 minutes post-handling. Notably, however, male fish exposed to netting +60 seconds of air exposure showed a delayed response whereby available aerobic scope was constrained <75% of maximum until ~4-6 hours post-stress. Larger fish showed a greater initial increase in oxygen uptake post-stress and slower rates of recovery. The results suggest that in the period following discard, this species may experience a reduced aerobic capacity for additional behavioural/physiological responses including feeding, territory defence and predator avoidance. These results are among the first to examine impacts of discard practises in the ornamental fishery and suggest ecophysiological research can provide valuable insight towards increasing sustainable practises in this global trade.

The size dependency of foraging behaviour: an empirical test performed on aquatic amphipods.

The behavioural choices made by foragers regarding the use of resource patches have a direct influence on the energy balance of the individual. Given that several individual traits linked to the acquisition of spatially distributed resources increase with body size (e.g., energy requirements, resource ingestion rates, and movement capacity), it is reasonable to expect size dependencies in overall foraging behaviour. In this study, we tested how body size influences the number, duration, and frequency of foraging episodes in heterogeneous resource patches. To this end, we performed microcosm experiments using the aquatic amphipod Gammarus insensibilis as a model organism. An experimental maze was used to simulate a habitat characterised by resource-rich, resource-poor, and empty patches under controlled conditions. The patch use behaviour of 40 differently sized specimens foraging alone in the experimental maze was monitored via an advanced camera setup. Overall, we observed that individual body size exerted a major influence on the use of resource patches over time. Larger individuals had stronger preference for the resource-rich patches initially and visited them more frequently than smaller individuals, but for shorter periods of time. However, larger individuals subsequently decreased their use of resource-rich patches in favour of resource-poor patches, while smaller individuals continued to prefer resource-rich patches for the whole experimental time. With body size being a key organismal trait, our observations support the general understanding of foraging behaviours related to preference, patch use, and abandonment.