How do you handle fish? Paul Moinester/Keepemwet Fishing photo.
You’ve hooked up on a fish. You fight it, reel it in, and get ready to land it. Do you reach for a net? A lip gripping device? Or just stick your hands in the water? And what do you do once you have ahold of the fish? Does it stay in the water? Does it go in a boat or a livewell?
How we choose to handle the fish we catch and release can have a huge impact on the health of those fish. Some of the negative effects of handling on fish we can actually see (such as the loss of scales or equilibrium) but many we cannot, either because they are invisible to the naked eye, are internal, or occur after we release the fish.
This study uses a clever way to examine some of the invisible injuries to fish and how different handling techniques impact the skin of fish. All fish are covered with an epithelial layer, which is on top of the scales and provides a barrier to pathogens, UV light, and desiccation (drying out). There is also mucus on fish, but the amount varies among species. Unlike with humans, the outer layer of cells on fish are living and a disruption to the epithelial layer creates a susceptibility to infection.
Fluorescein is a non-toxic dye that can be used to examine epithelial damage on fish (it is some of the same stuff used by detectives to look for blood at crime scenes). After being dipped in a solution containing fluorescein, areas on a fish with damaged epithelium with glow green under a UV light.
What did they do?
• Used fluorescein dye to examine how different handling methods damage the epithelial layer on largemouth bass and northern pike.
• Handling techniques included different types of nets, a lip gripping device, and placing a fish on a variety of boat surfaces.
• Largemouth bass from a semi-professional live-release tournament were also measured for epithelial damage.
• After being subjected to the fluorescein dye, fish were photographed under a UV light and damaged area (seen as green on the photos) was measured using computer software.
A northern pike photographed under UV light after being exposed to fluorescein dye. The green areas indicated epithelial damage from handling. Image from linked report.
What did they find?
• Northern pike had more epithelial damage than largemouth bass across all handling methods
• Largemouth bass from the tournament had the most epithelial damage. This isn’t surprising as they were often subjected to multiple handling methods, where the experimental fish were only subjected to one handling method.
• Rubber, non-knotted landing nets caused less damage than nylon, knotted nets for pike. For bass, there wasn’t a difference between net types.
• All fish placed on a boat surface had epithelial damage and those placed on indoor/outdoor carpet had more damage than those placed on a bare metal surface.
Why is this study important to anglers?
This study shows that different species can have different reactions to the same type of handling. This is one of the reasons the science of catch-and-release is so interesting and can be confusing, and why ‘one size fits all’ rules may not apply. Nevertheless, here are two generalities that we can uphold because they are supported by this study (and others) and follow the precautionary principle – the idea behind “better safe than sorry”.
• This study confirms what many anglers have thought for a long time; that softer, rubber, non-knotted nets are better for fish.
• Likewise, contact with boat surfaces (carpet or smooth metal) causes damage to fish and rough surfaces cause the most damage. I would argue that placing fish on any hard surface (rocks, logs, boats) either wet or dry has the potential to cause epithelial and internal damage to fish. Whenever possible, fish should be held over water deep enough for them to swim in. But remember, we also need to #KeepEmWet.
See the complete study here.
Happy Fishing!
Sascha Clark Danylchuk