Minimize angling duration The duration of the angling event increases the physiological disturbance from which the fish has to recover.  Angling results in a combination of aerobic and anaerobic exercise that causes a number of physiological changes such as the depletion of energy reserves, accumulation of lactate, and alterations in acid/base status.  Studies have shown that these physiological disturbances are generally more severe with increasing angling duration.  In addition, the length of time required for physiological variables to return to resting levels tends to increase with angling duration.  Therefore, anglers should try to land fish as quickly as possible to minimize the duration of the exercise and the related physiological disturbance.  There are techniques for achieving shorter angling durations, such as choosing equipment that matches the size of fish that are expected to be encountered.

Minimize air exposure Air exposure is harmful to fish.  Air exposure occurs upon capture when a fish is removed from the hook, weighed, measured and/or held for photo opportunities.  When a fish is exposed to air, the gill lamellae collapse causing the gill filaments to stick together.  This has several negative physiological implications.  It can cause severe anoxia.  Fish that are exposed to air typically experience greater acid/base disturbance (fluctuation of pH in the blood) than those which are not.  When fish are exposed to air for a significant length of time, they require a much longer time to return to their normal state.  Furthermore, extended air exposure (beyond a species-specific timing threshold) can eventually result in permanent tissue damage or death.  Although different fish species vary in their tolerance to air exposure, it is recommended to minimize the duration of the air exposure whenever possible.

Avoid angling in extreme water temperatures Most fish are ectothermic (they cannot regulate their own body temperature) so the environment regulates their temperature.  Any changes in the ambient water temperature can have a significant impact on their cellular function, protein structure, enzyme activity, diffusion rates and metabolism.  In addition, the amount of dissolved oxygen in water is lower at higher water temperatures.  Angling stressors tend to be magnified at higher water temperatures as reflected in strong relationships between water temperature and mortality for several species. On the other hand, extremely cold temperatures likely also have detrimental effects, although this has been poorly studied to date.   Although individual species exhibit different thermal tolerances, catch-and-release angling has the potential to be harmful at extreme water temperatures.  In some jurisdictions, there are restrictions on angling when water temperatures exceed some threshold. Since water temperature exerts control over almost all physiological processes in fish, extreme water temperatures are undoubtedly conditions in which fishes are most vulnerable and where angling should be avoided.

Use barbless hooks and artificial lures/flies Hooks are used to capture fishes.  Therefore, hook design is an important element to consider when attempting to reduce hooking related injuries and mortality.  Hooks with barbs can lead to greater injury than barbless hooks and even contribute to mortality, although the literature accounts are disparate. However, barbless hooks can minimize the amount of harm caused by reducing tissue damage at the point of hook entry and by reducing the amount of time required to remove a hook.  Since there is no barb, the hook can easily be removed.  Some studies show that circle hook can be an effective tool in catch-and-release fisheries, when used properly under certain conditions [see section on circle hooks].  The type of bait used is another important factor in fish injuries.  Live/organic baits (e.g., worms) used on hooks can be ingested and the hook becomes lodged into the viscera.  This makes it hard to remove the hook and it will likely cause damage to the vital organs/tissue during the process.  Artificial lures or flies do not get ingested as much so there is minimal damage to the vital organs/tissues from the hook(s).  Barbless hooks and artificial lures/flies can greatly reduce handling time, hooking injuries and the likelihood of mortality.

Refrain from angling fish during reproductive period The reproductive period is the time during which fish attept to produce off-spring and is thus critical for sustaining fish populations.  Angling fish during their reproductive period canl reduce the number of off-spring that could contribute the population.  Some species, like the largemouth bass, provide parental care and protection for their off-spring.  If this dad is removed from the nest, even for a brief moment, its off-spring become extremely vulnerable to predators.  Thus, angling immediately prior to or during the reproductive period could affect fitness and should be avoided.

There are a number of online sources with outreach materials that provide information on the subject of catch-and-release.  Some of the information may or may not be scientifically based.  Christine Pelletier, a Carleton undergraduate student, evaluated the on-line catch-and-release guidelines that were developed by various state and provincial natural resource agencies across North America.  The scope of this evaluation was to assess the consistency of the prescribed guidelines with the best available scientific information.