Increased tilapia embryo viability using ultraviolet irradiation in a closed recirculating Zuger-bottle system

The addition of an ultraviolet liquid sterilizer (UVLS) to a closed recirculating-water Zuger-bottle incubator considerably enhanced the viability of artificially fertilized eggs. The same amounts of eggs were incubated in two separate Zuger-bottle systems, equipped with thermoregulation (26°C) and charcoal filters and with or without UVLS. The difference in efficiency between these two systems increased over time following their extensive use during seven weeks. While the efficiency of these two systems was quite similar for eggs whose incubation starts up to the end of the first week (88%), the viability of the eggs incubated at the end of the fifth week (for an additional two weeks) was highly affected, mainly in the non-UVLS-equipped system (13·5%) in comparison to the UVLS-equipped incubator (60%). This decrease of viability seems to be due both to abrupt exhaustion of charcoal activity and to slow decrease of UVLS efficiency as a result of slime and mineral deposits.