Incubation
Incubation systems
Following tempering and egg disinfection, the eggs are placed in the incubation units for hatching which, depending on the water temperature, starts approximately 6-10 days after receiving the eggs.
Regardless of the incubator system used, care should be taken to keep hygiene levels at a high standard. This includes disinfection of footwear and hands before entering the hatching facility. Regular cleaning and disinfection of all equipment used is also recommended. If dead eggs appear they should be removed daily to prevent fungal infections, which can possibly harm normal eggs as the fungus (Saprolegnia) grows. Removing dead eggs can be time consuming and in case of large batches, chemical treatments can become necessary to control fungus infections. Adding formalin to the income water is very efficient but hydrogen peroxide can also be used.
Trout eggs should not be treated with formalin within 24 hours of hatching. Hatching eggs and sac fry are very sensitive and should not be treated with any chemicals.
Many different incubator systems exist but the most commonly used are one of the following three systems:
Regardless of the incubator system used, care should be taken to keep hygiene levels at a high standard. This includes disinfection of footwear and hands before entering the hatching facility. Regular cleaning and disinfection of all equipment used is also recommended. If dead eggs appear they should be removed daily to prevent fungal infections, which can possibly harm normal eggs as the fungus (Saprolegnia) grows. Removing dead eggs can be time consuming and in case of large batches, chemical treatments can become necessary to control fungus infections. Adding formalin to the income water is very efficient but hydrogen peroxide can also be used.
Trout eggs should not be treated with formalin within 24 hours of hatching. Hatching eggs and sac fry are very sensitive and should not be treated with any chemicals.
Many different incubator systems exist but the most commonly used are one of the following three systems:
1. California trays which are horizontal throughs usually made of glasfiber and each through holds 4-8 trays in series. The water is forced up from below and leaves the tray through the back side to go into the next one. One to two litres of eggs can be incubated in each tray, preferably the eggs should be in no more than a few layers to facilitate inspection and removal of dead eggs. An advantage of this system is that start feeding can begin in the trays when the fry swim up.
2. Vertical tray incubators, where the trays are arranged in stacks instead of the horizontal series that apply for the California trays. The water is re-aerated as it flows through the stack of trays which means that this system require relatively little water supply, and in addition, it takes up less floor space. The fry can be kept in the trays until swim up stages where they are transferred to other units for first feeding.
3. Upwelling incubaters are jars usually constructed from PVC, fiberglass or similar materials. The incubator is supplied with water at the bottom and the upwelling incubator will naturally force the sac fry out of the jar and into the rearing unit.
In general, it is advisable to monitor oxygen contents at regular intervals to constantly secure an adequate supply. The oxygen should preferably be no less than 8 mg / l in the outlets. Incubation temperature is also very important as temperatures above 11 C are potentially harmful to the eggs. In hatching units using ground water borehole water, gas supersaturation can become a problem. In additon, pumps drawing air in from the sucking site may increase gas pressure. Newly hatched fry are highly sensitive to even very small elevation in total gas pressure.