KEEPING NATIVE FRESHWATER FISH IN AQUARIA

How hard are they to keep?

Although they may be being kept in the same country in which they naturally occur, captivity, and aquaria in particular, is still a very different environment for NZ native freshwater fishes.

Temperature

Most native freshwater fish are relatively robust to many aspects of degraded water quality.  However, the seemingly unimportant parameter of water temperature may often be a deciding factor in whether a freshwater fish can successfully be maintained in either a natural environment; or captivity.

Warm water temperatures affect fish in many ways. They may;

1. Directly stress the animal.

2. Decrease dissolved oxygen concentrations.

3. Increase toxicity of other chemicals e.g., ammonia.

4. Increase population growth rate of diseases such as fungi.

The more sensitive native freshwater fish be become stressed as water temperatures near 20^oC. These species are mainly the galaxiids such as banded kokopu.  Bullies are generally more tolerant to warmer water temperatures and eels (especially the shortfin eel) are more tolerant again.  Fish species from cool environments may, however, be more sensitive to warmer water temperatures than other species in their families.

How to prevent temperature problems
Selection of appropriate species to the the region they will be kept in is clearly the first step. Alpine galaxias will no doubt be more difficult to keep in Northland than in Southland!

Location, size and type of aquaria or pond will also make great differences to water temperature. A tank or pond that receives direct light is probably going to become a lot more heated than one which is shaded all day.

The larger the water volume the slower the tank or pond will heat and cool as well. A larger water volume at least will decrease magnitude of temperature fluctuation which may reduce stress as well.

Finally, any extra form of insulation will slow heat gain in the holding water body. All-glass aquaria heat very quickly as glass is a poor heat insulator. Aquaria sides made of wood or insulated with sheets of polystyrene (see picture below) may help here.

Insulated sides and plastic bottles of ice may be used as a
short-term measure to cool native freshwater fish aquariums down.

How to prevent temperature problems
Water temperatures may still become problematic, for instance over hot summer months. A short-term solution to warm water may be to use plastic bottles of frozen water. Using bottles avoids both excess water building up in the vessel and also issues of contaminants being introduced with the water. These cooler temperatures may not last long, however, and ongoing solutions to warm water may require some more serious engineering solutions.