During the early-rearing stages, fish are more susceptible to disease, so it is imperative to use the best water in your hatchery system.
A good start is critical to the long-term growth and survival of the fish. During the early-rearing stages, fish are more susceptible to disease, so it is imperative to use the best water in your hatchery system. Water should always be “first-use” and should preferably be from an isolated, uncontaminated spring or well (borehole) as stream or river water may often become turbid with fine particles that are not ideal for eggs or alevins. If stream or river water is used, then some form of filtration should be included at the intake point in the hatchery design. Ideally, hatchery systems should be flow-through (single pass) and utilize cold, pathogen-free water. There is increasing use of re-circulated water in hatcheries although it is essential to ensure good filtration and sustained oxygen levels as recommended under water parameters in the next section.
If there is any possibility of incubating water becoming turbid it is recommended to use some form of filtration before the water enters the incubators and particularly the early rearing ponds as suspended solids (even very fine solids) should be avoided as they are harmful to the gills of the alevins and can cause various complications and mortality. Various filters are available including sand and micro-screen drum filters as pictured.
Microscreen drum filter
The use of ultra-violet or ozone treatment should be considered in recirculation systems or if there is any possibility of any bacterial contamination in the flow-through system.
Ultra Violet (UV) filters
The following are the optimum water quality parameters for incubating eggs, hatching eggs and early stages of the alevin and fry life cycle:
Water Temperature °C
Oxygen Saturation %
Carbon Dioxide mg/ml
Dissolved Gas (Nitrogen) %
Table 1. Water Quality Parameters for Rainbow Trout Eggs and Juveniles
Different hatching systems may demand different water flows but as a general rule, in a flow –through or “single pass” system, a minimum flow of 4-6 litres per minute per 100.000 eggs at temperatures below 15⁰C (59⁰F )is recommended to provide adequate oxygen. The oxygen saturation of water is dependent on temperature so, at temperatures above 15⁰C (59⁰F), the flow should be increased. If possible the oxygen levels should be monitored and should not fall below 6 ppm (parts per million). In some re-circulated systems it may be necessary to introduce oxygen to the water if the levels fall below those recommended.
The amount of water flowing through eyed-eggs should not be excessive, moving the eggs too rapidly or violently, although an agitation or slight tumbling of the eggs in the incubators (especially upwelling incubators as will be described further in this guide) is useful to prevent the growth of fungus such as Saprolegnia sp. and also to remove/wash off egg shells when the alevins start to hatch.