It is virtually impossible to determine the quantity of fish to be kept in a system purely on a weight or number of fish per unit volume or area of water surface area.

The variation in holding system used, the quality of husbandry and the types of fish stocked vary so greatly that it would render any such system too complicated to be practical or too simple to be useful.

The maintenance of water quality standards can be used to determine working stocking densities.

Water quality criteria

Cold water
Dissolved Oxygen Free Ammonia Nitrite Nitrate	min - max - max - max -	6mg/litre 0.02mg/litre 0.2mg/litre 50mg/litre above ambient
Tropical Freshwater
Dissolved Oxygen Free Ammonia Nitrite Nitrate	min - max - max - max -	6mg/litre 0.02mg/litre 0.2mg/litre 50mg/litre above ambient
Tropical Marine
Dissolved Oxygen Free Ammonia Nitrite Nitrate pH	min - max - max - max - min -	5.5mg/litre 0.01mg/litre 0.125mg/litre 40mg/litre ambient 8.1

Guide stocking densities

The water quality standards should not be met at the expense of a correct feeding regime.

Cold Freshwater

8kg/1000 litres

Tropical Freshwater

Fish up to 2" - 1.5kg/1000 litres
Fish over 2" - 2.5kg/1000 litres

Tropical Marine

Fish up to 2" - 1kg/1000 litres
Fish over 2" - 2kg/1000 litres

Guide stockings are ADVISORY only. They may be exceeded if the water quality standards are satisfied. When the water quality standards are exceeded at a lower stocking, this must then be considered as the maximum stocking density permissible.

The TOTAL volume of the system must be measured and taken into account in determining actual stocking densities.