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Water quality is of paramount importance to the welfare of fish stocks, and intensive stocking can have serious adverse effects on water quality. Therefore water quality parameters, especially dissolved oxygen (DO) and ammonia (NH₃) should be measured on a regular basis, and action taken if necessary. The lowest oxygen levels normally occur at dawn, and the highest at dusk.

• Obtain a suitable oxygen meter and measure DO at dawn, dusk and 4 hours after dusk; also by day when hot and/or cloudy.
• Measure NH₃ – kits are best but this also requires temperature and pH measurements followed by simple calculations to obtain NH₃figure.
• Watch out for algal blooms and oxygen sags.
• Aim to keep DO above 3mg/l (at dawn) and unionised ammonia (NH₃) below 0.1mg/l.
• Provide aeration if:
  • Feed rate exceeds 35lb/acre/day.
  • Unionised ammonia (NH₃) levels above 0.1 mg/l.
  • Algal blooms present.
  • Dissolved oxygen falls below 3 mg/l or fish display symptoms of oxygen shortage.

No stock manipulation should be undertaken unless the true status of the resident stock is known. Only fish from a known source and acceptable health status should be considered for introduction. Anglers’ bait is an essential part of the diet of fish in intensive fisheries; therefore the number of anglers using a fishery and the frequency with which they fish is important in determining the biomass of fish that will survive.

Management of water quality will be necessary in intensive fisheries to maintain fish stocks and avoid mortalities. Where biomass is in the range 1000-2000kg ha^-1, equipment to maintain water quality is highly desirable. Biomass should not exceed 2000kg ha^-1

• Less than 10 anglers/ha/week <800kg ha^-1 (not an intensive fishery)
• 10-25 anglers/ha/week 800-1000kg ha^-1
• 25-50 anglers/ha/week 1000-2000kg ha^-1
• More than 50 anglers/ha/week 2000kg ha^-1

FISH HEALTH

Healthy fish are essential to the success of a fishery. While high stock densities can provide reliable sport, all fish introductions carry riks to the health of the existing stocks, and therefore stocking should only be carried out where absolutely necessary, and only after careful consideration and planning.

Do

• Ensure the conditions provided in the fishery are suitable for the resident species not only to survive, but thrive, grow and develop.
• Minimise the introduction of new disease agents. - by far the greatest risk of disease introduction exists from direct fish introductions.
• Ensure new introductions are health-checked prior to stocking.
• Maintain optimal conditions within the fishery.

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