Congridae leptocephali in the open waters of middle and south Adriatic Sea

Individuals of Congridae leptocephali were accidentally caught during targeted research of small pelagic fish with small pelagic trawl nets (Italian-type otters) in the open waters of middle and south Adriatic during September 2010-2014. A total of 51 Conger conger, 19 Ariosoma balearicum and 3 Gnathophis mystax leptocephali were identified on the basis of their morphology, morphometric and meristic characteristics and pigmentation. 41 C. conger leptocephali were in premetamorphic stage, while 10 were in metamorphosis. The total number of myomeres ranged from 148 to 156, while the numbers of preanal myomeres differ for premetamorphic and metamorphic ones (75-81 and 55-57 respectively). According to morphometric and meristic characteristics of A. balearicum and G. mystax, all were in the premetamorphic stage. The total number of myomeres for A. balearicum varied between 125 and 134 and preanal myomeres from 108 to 112, while for G. mystax ranged from 134 to 137 and 114 to 117, respectively. The hatching dates back-calculated from the otolith microstructure of the field-caught C. conger leptocephali (8 to 11 months old) indicate a spawning season from late December through late August, with one annual peak occurring in August - September at the end of the warm season. Based on the age and distribution of leptocephali, as well as the upper-layer circulation and modelled mean current fields, a possible scenario of retention and dispersion of larvae suggesting South Adriatic Pit (SAP) as spawning area of Congridae species is explained.