Otolith microstructure, age and growth of two species of Ceratoscopelus (Oosteichthyes: Myctophidae) from the eastern North Atlantic

Abstract The otolith microstructure of Ceratoscopelus maderensis (Lowe) and C. warmingii (Luetken) was studied with light and scanning electron microscopy. The two species have a similar otolith structure consisting of a central core with outward radiating aragonite crystals forming increments. Growth increments were well defined over most of the sagittal sections of otoliths except in the transitional area around the core and outermost parts of the largest C. maderensis otoliths. The ages of 39 C. maderensis and 37 C. warmingii were estimated by enumeration of otolith increments that were postulated to be daily. The ages of an additional 40 C. maderensis were estimated from otolith weight through the use of a regression model. No differences in size of males and females were observed in C. maderensis while in C. warmingii females were larger than males. Ceratoscopelus maderensis was characterized by linear growth during the first 6 months of life, attaining over 40 mm SL at that age. A reduction in growth rate occurred at an calculated age of about 10 months and a size of 50 mm. This coincided with the winter season and sexual maturation. Only a few specimens over 2 years of age were observed, an indication of a high mortality during the second year of life, although sampling bias may have contributed to the lack of abundance of older fish. With this consideration the growth parameters of the von Bertalanffy equation estimated for C. maderensis were K = 1.3 and L ∞ = 79.0 mm . For the C. warmingii samples analyzed, males attained lengths of 46–47 mm at 9–10 months of age, while females lived over 1 year and reached 64–68 mm. A noticeable decrease in growth in males was prominent at the larger lengths, whereas, the growth of females was linear to the maximum size captured.