Seeing in the swamp: hydrogen sulfide inhibits eye metabolism and visual acuity in a sulfide-tolerant fish

In fish, vision may be impaired when eye tissue is in direct contact with environmental conditions that limit aerobic ATP production. We hypothesized that the visual acuity of fishes exposed to hydrogen sulfide (H 2 S)-rich water would be altered owing to changes in cytochrome c oxidase (COX) activity. Using the H 2 S-tolerant mangrove rivulus ( Kryptolebias marmoratus ), we showed that a 10 min exposure to greater than or equal to 200 µM of H 2 S impaired visual acuity and COX activity in the eye. Visual acuity and COX activity were restored in fish allowed to recover in H 2 S-free water for up to 1 h. Since K. marmoratus are found in mangrove pools with H 2 S concentrations exceeding 1000 µM, visual impairment may impact predator avoidance, navigation and foraging behaviour in the wild.

Investigating fish behavioural responses to LED lights in trawls and potential applications for bycatch reduction in the Nephrops-directed fishery

Light-emitting diodes (LEDs) have been tested in trawl fisheries to reduce the bycatch of unwanted species through behavioural stimulation. Previous studies used LED lights to either highlight escaping routes or increase the contact rate with square-mesh panels. However, phototactic responses (moving towards or away from light sources) to LED lights could also be exploited to separate species during the catching process. We investigated if either positive or negative phototaxis can be used to improve fish vertical separation from Nephrops (Nephrops norvegicus) in the aft section of a horizontally separated trawl codend. The aim was to increase the proportion of fish entering the upper compartment. We conducted two different experiments in front of the separation into compartments, inserting green LED lights in the upper and lower netting panel, respectively. Species vertical separation was analysed and compared in two identical trawls towed in parallel, one equipped with lights and one without. We obtained significant changes in vertical separation, but no clear species-specific phototactic response was identified. Neither of the light positions improved fish separation from Nephrops. However, the potential of LED lights as behavioural stimulators is confirmed, and a more mechanistic understanding of light and fish vision may improve the results of future applications.

General editorial

In the past two years the field of fish vision research has lost three central figures, Bill McFarland, Bill Muntz, and Joe Bilotta. This volume of Visual Neuroscience is dedicated to them. Since the inception of this volume, Henk Spekreijse and Adam Locket, who made significant contributions to fish vision, have also passed away; they are also remembered.