Some observation on the length frequency distribution and gonad development of longtail Tuna in Iranian Waters

Abstract

Sampling of longtail tuna (Thunnus longgol) wa conduced during each delivery of tuna catch to the tuna. canning Factory in Bandar-Abbas, Length frequency data was collected on a monthly basis. All individuals in the samples were examined for sex identification. The maturity stages for females were determined according to a 5 point scale.For the purpose the gonad index based on the weight of the fish was applied, most longtail tuna captured off the alost coast Iran principally from the Gulf of Oman arc considerably larger ranging from 75 to 80 Cm fork length. Fish below 55 Cm length were not represented in the samples. This results provide no modal progession for the monthly lenght frequency. Thy possible sourocs creating bias in the length distribution data such as migratory nature of longtail tuna and gear selectivity has been discussed. Thc study on the maturity magos reveals. that the spawning season for longtail tuna captured in Iran from the sea of Oman extraids from August through October. The possible multiple spawning season for this species has also been discussed.