Length composition of Rutilus kutum caught in darkness and brightness

Fishing and exploitation of bony fishes has been carried out in the Iranian waters of the Caspian Sea since the past to now. Currently more than 10,000 people are active in fishing companies and exploited of bony fishes by beach seine in second half of the year. The Rutilus kutum is the most important and most economical species among the bony fishes, and its main catch carried out from February to April. Investigating the length composition showed that exploitation of young and immature fishes increases dramatically during darkness. The percent frequency of non-standard fishes in time of darkness and brightness was calculated 76.4 and 52.1% respectively in 2016-2017 in Mazandaran province. By avoiding fishing during dark hours and limiting the time of fishing in the dark, the pressure on the stocks of the Rutilus kutum will decrease. This goal is require to good communication and people awareness among the exploiting community.