Atherina boyeri is the dominant fish species in Lake Trichonis (Greece) and the target species in the professional purse seine fishery, conducted mainly during the night by the use of lamp rafts. A recent study on its diet when fed close to the fishery lights showed that it is capable of preying large numbers of larvae of the native and endangered fish Economidichthys trichonis. This study reports the first results of a conservation program aiming to the reduction of this predation by A. boyeri. Stomach content analysis, applied on specimens of A. boyeri caught around lamp rafts of the purse seine fishing conducted between May and December 2017, revealed that among seventeen prey categories, the E. trichonis larvae were second in frequency of occurrence after the larvae of the mollusk... Dreissena blanci. Each of the larger A. boyeri specimens was able to consume up to 14.5 (± 7.98) E. trichonis larvae in certain periods, with a maximum number of 51 larvae being consumed by a single individual. The predation pressure exercised on these larvae by the A. boyeri school aggregated around the lights of a single purse seine fishing boat, reached a maximum of about 260,000 (SE = 43,000) specimens per night in June with a second peak in November (220,000 ± 42,000). This study verifies the previous findings about the predation pressure that A. boyeri can exercise on other fish species of the lake due to the specific fishing practice and points out the need of alteration in the fishery legislation, along with estimates of the current population size of E. trichonis in Lake Trichonis. Considering that fishing with light is exercised in various forms all over the world, this investigation may be considered instigation for more studies worldwide in order to evaluate the actual ecological consequences.