Reproductive biology of the Electric lanternfish Electrona risso (Myctophidae) and the Bigscale fishes Melamphaes polylepis and Scopelogadus mizolepis (Melamphaidae).

Key reproductive traits of the Electric lantern fish Electrona risso (Myctophidae, n = 918) and the Bigscale fishes (Melamphaidae) Melamphaes polylepis (n=260) and Scopelogadus mizolepis (n = 649) were investigated for the first time. Specimens of these mesopelagic species were collected in March and April 2015 in the Eastern Central Atlantic (0 - 24° N, 20 - 26° W). Sex ratio was not significantly different from 1:1 in E. risso and M. polylepis, but significantly skewed towards female dominance in S. mizolepis. Reproductive phases were determined macroscopically, and by histological analyses on selected individuals. Female length at 50% maturity (L 50 ) was 55.1 mm standard length (SL) in E. risso, with an observed female maximum length (L max ) of 81.2 mm SL. M. polylepis females had an L 50 of 40.2 mm SL and L max of 86.7 mm SL. S. mizolepis had an L 50 of 46 mm SL and L max of 97.9 mm SL. The three species show histological features of iteroparity, but the E. risso population appears to occur in two year-classes and experience only one spawning season per lifetime in the study region. All three species are batch spawners. A batch fecundity of 2668 eggs was estimated from one E. risso individual, with a relative batch fecundity of 369 eggs g -1 gonad-free body mass. M. polylepis had a batch fecundity of 1027 eggs and a relative batch fecundity of 149 eggs g -1 (n = 3). S. polylepis had a batch fecundity of 1545 eggs and a relative batch fecundity of 215 eggs g -1 (n = 21). The median Gonadosomatic Index during the actively spawning phase of E. risso was 4.5, significantly lower than that of M. polylepis (7.5) and S. mizolepis (7.1). No regressing or regenerating phases were observed in this study. Batch spawning in all three species is suggested to be advantageous to cope with intra-annual variability in food supply and other risks for offspring survival. With what appears to be in effect a (facultative) semelparous strategy in combination with a short lifespan in E. risso, inter-annual differences would have a great influence on population dynamics of this species. Knowledge is still lacking on temporal aspects of reproduction such as the duration of the spawning season and the frequency of spawning, as well as age and growth. This article is protected by copyright. All rights reserved.