Age, growth and sexual dimorphism of the monkeyface prickleback (Cebidichthys violaceus)

Accurate estimates of age, growth and maturation are fundamental to fisheries assessment, conservation and the development of emerging aquaculture species. However, life-history parameters can vary within species and may be influenced by factors such as sexual dimorphism, which is often poorly quantified in non-commercial or understudied species. The monkeyface prickleback (Cebidichthys violaceus), one of the largest herbivorous fish along the west coast of North America and a potential aquaculture candidate, remains relatively understudied with respect to life-history variation and sexual dimorphism. This study updates and expands previously reported life-history parameters of C. violaceus by incorporating a wider size range of individuals, including juveniles, and evaluates sexual dimorphism in cranial morphology using geometric morphometric methods. Von Bertalanffy growth functions based on otolith sectioning and updated length-weight relationships were developed for adult males, females and all fish combined. Length and age at maturation were estimated to be earlier than previously reported, with most individuals maturing before 28.2 cm in length and 5 years of age. Females were generally heavier than males of the same length, whereas males were longer than females of the same age and attained greater maximum lengths. Condition factor only differed between adult males and juveniles. Sexual dimorphism was assessed using body metrics and quantified through geometric morphometric analyses of head and supraorbital crest shape. Head shape, supraorbital crest shape and eye size differed significantly between sexes, with morphological differences becoming more pronounced with increasing body size, providing clear evidence of sexual dimorphism in adult C. violaceus. These findings will aid in the sustainable management of wild populations and optimise broodstock selection and aquaculture development for the species.