line caught fish catch and release, all this applies.

From these issues that severely affect all fishes survival, for line caught fish that need to be released, it is best to get them to the boat and release them as fast as possible instead of prolonging the time they are “played” at the end of the line.

Many anglers hold onto a fish that they’ve captured and move it forward and backward in the water to try and revive it.

Part of this is good, part of it is bad.

Fish gills are designed to have water flow in one direction, not two, because they have what is called a counter-current exchange system in their gills.

As water flows from the front to the back of the fish (into the mouth, across the gills, and out the operculum), blood flows in the opposite direction, from back to front, through the gill filaments.

This allows for a substantially greater uptake of oxygen from the water than if both water and blood were both flowing in the same direction.

This is similar to the way in which a heat pump works.

The problem with moving a fish backwards in the water is that it defeats the counter-current exchange system and reduces the amount of oxygen a fish can get.

This, in turn, prolongs the time to recovery.

So the best option if the fish needs reviving is to hold it still and point it into the current, or to have the vessel move forward at idle speed, allowing water to flow across the gills in the correct direction.

When the fish actively moves out of your hands, let it go.

Want to do something else that is really bad for a fish and create undue stress?

Stress it by picking it up by its tail.

Fish (especially fast swimmers like tuna) have spines that are designed to resist compression forces, not expansion (lengthening).
The lateral swimming muscles on a fish attach at two points on the spine.

When a fish swims, it contracts these muscles on one side of its body, and then the other, creating a ripple or wave down the side of the fish.

The muscle pulls the spine towards its side of the body and compresses the spine as the two ends of the muscle move closer together.
Picking up the fish by its tail stretches the spine, causing muscle, nerve and spine damage.

With albacore you can sometimes actually feel the vertebrae popping.

This is bad for a fish, and reduces its chance for survival.

In addition to stretching the spine, grabbing the fish by the caudal peduncle (the narrow part at the base of the tail) causes bruising, which can allow infection to set in.

Either leave the fish in the water and reach down to remove the hook, or net it in a fish-friendly net.

Studies at the NOAA Fisheries Alaska Fisheries Science Center Facility in Newport, Oregon, have shown that some species of fish are very susceptible to succumbing to capture-related stress.

In some of their experiments simulating fishing, as little as 15 minutes of stress resulted in substantially compromised immune systems in sable fish.

Furthermore, pollock exposed to a simulated fishing event for 15-30 minutes survived the initial stress, but had altered behaviour patterns and never started feeding again.

These fish were substantially more likely to be eaten by predators, and those that weren’t eaten died from stress related causes 2-3 weeks later.

In other words they survived the initial stress but ultimately it was too much for their system to deal with.

We do not know the specifics about the stress response in many of the species for which we fish, so until we do it is best to treat the fish you release as gently as possible, and to get them off the hook and back in the water as quickly as possible.

A lot of the work that has been done studying stress in fish has been done by Dr. Carl Schreck and his students and technicians in the Department of Fisheries and Wildlife at Oregon State University.
More information on Dr. Schreck’s work can be found in the scientific literature and in several book chapters that he has written on the subject.

Long-term or chronic stress can slow or stop growth, due in part to cortisol released in response to stress that affects the metabolism of carbohydrates, lipids, and proteins.

Stress can prevent reproductive activity while energy that is normally directed toward spawning is diverted to the more immediate needs of homeostasis.
Fish have a limited amount of energy, and stress increases energy demand.

Chronic or continuous stress keeps the metabolism running at a faster rate because of this increased energy demand.
This consumes energy, oxygen and glucose (Barton and Iwama, 1991).

The normal functions of physiological equilibrium such as respiration, tissues repair, locomotion, and hydro mineral regulation take priority over the investment activities of reproduction and growth.

This means the diversion of energy to deal with an elevated metabolism means that less is available for growth and reproduction.