Abstract

The objective of this research is to determine the effectiveness of a closed system in fish culture. The system consists of 36 20-gallon tanks whose water is filtered centrally by means of passing rotating biological contactors, through a diatomaceous earth filter, and finally past a UV sterilizing light before being returned to the tanks. Fish used for the study were channel catfish fingerlings. Selected water quality parameters were measured twice weekly. The expected nitrification cycle was demonstrated. To determine the effectiveness of the central filtration unit and UV light Ichthyophthirius was added to selected tanks within the system. The parasite spread to all other tanks. This experiment remains to be repeated along with further experiments using virus and bacteria. An infestation of Costia was treated using malachite green and formalin with no ill effects on the biological filter. Further work on all phases of this closed system needs to be done before any conclusions can be drawn.

Notes

A disadvantage of a closed system is nitrate build-up.

A bio filter used in domestic sewage treatment is effective in aquarium water filtration.

The fish were fed a flake food diet supplemented with liver and vitamins.

Water analysis:

• Spectrophotometer and pH meter used.
• Parameters - pH, temp., NH₄N, NO₂N, NO₃N, CO₂, hardness.

Ammonia excretion by fish causes multiplication of Nitrosomonas which converts NH₄ to NO₂, eventually leading to NO₃ (nitrate).

NaCHO₃ buffer is needed to keep the pH up
MgSO₄
KC1

Treatment of Costia infestation:

• 25 ppm formalin
• ppm malachite green
• Liver and vitamins
• Water change

A system is being devised which will contain a pathogen within a tank rather than allowing it to spread throughout the system.