Age, growth and mortality of the toadfish, Halobatrachus didactylus (Schneider, 1801)(Pisces: Batrachoididae), in the Bay of Cádiz (southwestern Spain)

Abstract

Age, growth and mortality of the toadfish, Halobatrachus didactylus , were determined by examination of the whole sagittal otoliths of fish sampled in the Bay of Cadiz (southwestern Spain) from March 1999 to March 2000. A total of 844 specimens (425 males, 416 females, and 3 of indeterminate sex), ranging from 95 to 470 mm in total length were examined. Eighty-nine percent of the otoliths could be read allowing an age estimation. The opaque zone was formed between April and May coincident with the maximum reproductive peak, while the translucent zone formed mainly in summer-fall (June to December). Maximum ages for males and females were 12 and 10 years, respectively. The samples were dominated by 2- to 6-year-old specimens. Males matured at an age of approximately 2 years and females at 3 years. Fish total length and otolith radius were closely related (r 2 >0.80). The von Bertalanffy growth curve was used to describe growth. The parameters were derived from back-calculated length-at-age. Significant differences in the growth parameters were found between sexes (in males L ∞ = 477.06 mm, K = 0.15 and t 0 = -0.59; in females L ∞ = 363.69 mm, K = 0.20 and t 0 = -0.75). Although the growth analysis revealed that this species is slow-growing, males reached larger sizes than females. Females appeared to experience higher natural mortality rates than males.