Catch and Release Guidelines

Livewell Management and Oxygen Injection

Black bass tournaments are popular in Texas. Nearly all bass tournaments require the release of live fish weighed in and penalize those with dead bass. Conservation of the resource should be a major consideration, and tournament anglers should do everything possible to ensure the survival of tournament-caught fish held in livewells and released. Achieving high survival of tournament-caught bass requires proper management of livewell water quality. The B.A.S.S. publication Keeping Bass Alive summarizes general methods to manage livewell water quality, and Texas Parks and Wildlife (TPWD) recommends these procedures to minimize stress on bass during many tournament situations. However, TPWD research also indicates that standard aerator/recirculation pumps in modern bass boats can be inadequate at maintaining sufficient oxygen levels in livewells during more extreme conditions (i.e., warmer water temperatures with higher fish weights) that regularly occur in tournaments at many Texas reservoirs.

Dissolved oxygen is the most important factor relative to minimizing stress and mortality on livewell-held bass. Warmer water naturally holds less oxygen than cooler water. At a moderate water temperature of 70˚F, 100% oxygen saturation is 8.9 ppm, whereas at higher temperatures of 80 and 90˚F, saturation declines to 8.0 and 7.3 ppm, respectively. Bass also consume more oxygen at warmer temperatures due to higher metabolism. These factors imply that extra effort is required during warmer months to maintain sufficient oxygen levels and prevent stress and mortality of bass. When water temperatures are greater than 80˚F, mortality rates can exceed 50% if additional steps aren’t taken to maintain adequate oxygen levels.

Oxygen levels less than 5.0 ppm are harmful to bass, especially if allowed to remain this low over extended periods. Very low dissolved oxygen (less than 2 ppm) can kill bass quickly, and bass challenged with 2 to 5 ppm dissolved oxygen may be alive at weigh-in but often die within 24 to 48 hours after release. TPWD data indicate that during warmer months, potential oxygen depletion in livewells is rapid with no aeration. With 14 and 17 pounds of Largemouth Bass (5 fish), oxygen levels were stressful (< 5 ppm) after 12-15 minutes and were projected to be lethal at 30 minutes (< 2 ppm).

TPWD defines sufficient dissolved oxygen levels to be 7.0 ppm or greater. At 85˚F with 14 pounds of Largemouth Bass (5 fish), running factory recirculation pumps at a timed interval (pumps running for 1 minute then off 2 minutes) resulted in stressful oxygen levels in only 27 minutes. With 19 and 22 pounds of bass, continuous operation of factory recirculation pumps resulted in oxygen below sufficient levels after only 15 minutes, and oxygen was maintained only slightly above stressful levels after 30 minutes (5.0 - 5.1 ppm).

TPWD evaluations using numerous combinations of bass boat brands and pump types indicate it is difficult to maintain sufficient oxygen levels with factory pumps at warmer water temperatures with heavier weights. However, an oxygen injection system can maintain sufficient oxygen levels in livewells, even under the most extreme conditions. This system is comprised of an oxygen bottle, oxygen regulator, hose, a tee, and two micro-bubble diffusers (one diffuser in starboard livewell and one in port livewell). When compared to factory recirculation pumps, the primary difference with this oxygen system is that 100% oxygen is injected into livewells, compared to the air (21% oxygen) introduced via the recirculation pumps.

TPWD conducted numerous trials with various rates of oxygen delivery and determined lowest flow rates (to maximize longevity of oxygen bottle) that maintained sufficient oxygen levels. At extreme conditions (85˚F water temperature and total 5-fish weights of 21 and 28 pounds), an oxygen flow rate of 0.25 liters per minute (LPM) maintained oxygen levels of 14 to 22 ppm over nine hours (much higher than the minimum sufficient level of 7 ppm). These trials were conducted without running recirculation pumps. If pumps are also used, oxygen levels will be reduced to levels slightly above saturation levels (around 8.5 ppm instead of 14 to 22 ppm observed in trials). Agitation of the livewell water by the pumps forces the supersaturated oxygen out of the water.

View the Livewell Oxygen Injection presentation with Powerpoint or SlideShare. The presentation includes additional details regarding oxygen system components tested by TPWD, as well as  installation, operation, and safety information.

Accumulation of potentially toxic metabolic waste products in livewells (ammonia and carbon dioxide) is an additional concern over an entire tournament day. Partial livewell water exchanges have been recommended to lower concentrations of ammonia and carbon dioxide, but these exchanges are problematic when also adding ice to cool livewell water and uniodized salt to aid with osmotic regulation (as recommended by Keeping Bass Alive ). However, TPWD evaluations have indicated that when running an oxygen injection system without using recirculation pumps, levels of ammonia and carbon dioxide do not reach stressful levels over a 9-hour period, even with a 5-fish weight of 28 pounds. The potential toxicity of ammonia decreases with decreasing pH, and not running pumps allow carbon dioxide to build up to non-stressful levels that reduce pH of the livewell water and reduce ammonia toxicity.
TPWD results regarding lack of ammonia toxicity were at a natural pH of 7.5. Natural values of pH can  commonly be 8 to 9, and at these higher levels, livewell ammonia levels could reach stressful levels.

ClorAM-X®, an inexpensive water conditioner commonly used in the aquaculture industry, can  neutralize ammonia in livewells at any pH value. TPWD data indicate that a single dosage of 1 tablespoon per 10 gallons of water will remove all ammonia toxicity over an entire 8- to 9-hour tournament day. ClorAM-X® is approved by the U.S. Food & Drug Administration (FDA) for use on food fish, which is important as tournament-released bass could be recaptured and eaten after release. Although similar water conditioners are also available, they lack FDA-approval for use on food fish.

TPWD Recommendations

Additional livewell management procedures recommended by TPWD:
Keeping Bass Alive
Fizzing Fish

For additional questions regarding tournament-related mortality, livewell management, oxygen injection systems, and fizzing fish, anglers can contact Todd Driscoll, TPWD Inland Fisheries, at 409-698-9114; todd.driscoll@tpwd.texas.gov.