Hatchery Quality Assurance Program - NSW Department of Primary ...

7 Water
quality
Fig. 7.1 Meter used to measure water quality variables.
24
NSW Department of Primary Industries | Water quality
7.1 - SUMMARY
Successful hatchery production of native fish
depends on the maintenance of good water
quality. Poor water quality will either kill eggs,
larvae or fish directly, or cause stress leading to
reduced feeding, slow growth, inhibition of
gonadal development and reproduction, and
increased susceptibility to disease. The water
quality variables temperature, dissolved oxygen,
pH, and ammonia should be regularly monitored
using meters and appropriate equipment, and
accurate records should be kept. All facilities
must be aerated and have a capacity for
exchange of water.
7.2 - GENERAL
Water quality in freshwater aquaculture is
discussed in detail by Boyd (1982, 1990) and in
relation to Australian fish by Rowland (1995b,
1998a). Key variables and relevant values are
listed in Table 5.1. Eggs and larvae usually have
more stringent requirements than juveniles and
adults, and so the quality of water for fish
hatcheries must be high.
The relatively stable variables of alkalinity,
hardness, conductivity and metals need to be
analysed during site selection; however, they
are not greatly influenced by fish culture
activities and so do not need to be regularly
monitored (other than alkalinity in RAS).
Temperature influences all chemical and
biological processes, and has direct effects on
dissolved oxygen concentration (DO), pH and
ammonia. These variables are unstable and are
significantly influenced by fish culture activities;
DO, pH and ammonia can change from acceptable
levels to stressful or lethal levels within
several days, particularly in summer (and within
a few minutes in RAS).
There is a strong link between water quality and
fish health – the susceptibility of fish to disease
is greatly increased by poor water quality. Water
quality can deteriorate rapidly in larval rearing
ponds where there are often large blooms of
phytoplankton and zooplankton, and a large
biomass of fish. Consequently, these four
variables must be monitored regularly. DO is
lowest near dawn, whereas maximum levels of
pH and ammonia usually occur in mid-afternoon.
The water quality monitoring program used at
GAC is given in Table 7.1.