Assessing maturity, fecundity and hermaphroditism in blue cod Parapercis colias

Abstract

Macroscopic assessments of maturity from whole fish gonads are well established and routinely used in fisheries research and are important in the estimation of size-at-maturity and the impacts of size-selective fishing. Histological assessment of maturity is more accurate, but much slower, more expensive, and so less frequently conducted. We made a comparison between macroscopic and histological maturity classifications for a diandric protogynous hermaphrodite, blue cod Parapercis colias. The agreement between macroscopic and histological maturity classifications was low. Female and male L 50 (length at which 50% of the fish are mature) was estimated from histological data as 23 and 26 cm, respectively. Female spawning frequency was 4.6 d, and mean ± SD relative batch fecundity was 6.5 ± 3.3 hydrated oocytes per gram body weight. A single gonad with both testicular and ovarian tissue was found. Many blue cod were assigned incorrect maturity classifications. These results warrant a study of early gonadal development in blue cod to elucidate if and how sex change takes place. Difficulties in determination of sex and maturity may be most pronounced for species, like blue cod, that have complex maturation patterns. For blue cod, a review of the macroscopic maturity classification key and more thorough technician training are called for.

Life history traits vary between geographically distinct populations in a protogynous hermaphrodite

“…Endemic to New Zealand's temperate reefs, blue cod are one of the most commonly landed commercial and recreational species (Carbines, 2004). Blue cod are protogynous hermaphrodites, with individuals maturing as male or female initially and some females changing into males later in life (Brandt et al, 2017; Carbines, 2004). They are thought to live in a harem structure where a large male shares his territory with three to five smaller females (Mutch, 1983).…”

Maturation of female common snook Centropomus undecimalis: implications for managing protandrous fishes

“…The proportion of females is used as a proxy based on the assumption that there is no delay in maturing following transition to the terminal sex ( i.e ., no immature phase as the terminal sex). In many species, whether an animal is mature can be determined through macroscopic techniques, but histological examination of gonads provides a more accurate characterization of the reproductive state (Brandt et al ., 2017) and is often used to verify sex and reproductive phase, including distinguishing the immature phase of the terminal sex (Alonso‐Fernandez et al ., 2011; Klibansky & Scharf, 2015).…”

Genome assembly of Parapercis colias (Blue cod/Rāwaru); An endemic marine fish species of New Zealand

“…These fish have been shown to be highly charismatic and the large males can be highly territorial (Carbines, 2004;Smith, 2012). This family displays an interesting sexual function that is sequential protogynous hermaphroditism, where females transition sex to become terminal males if the previous terminal male dies (Brandt et al, 2017;Carbines, 2004;Mutch, 1983). This is also known to be associated with sexual dichromatism where there is a difference in size, colour and pattern.…”

“…As the size/age structure and sex ratio of the population changes so does over all fecundity effecting the yield and demographic of the population and therefore the local stock. If there is to be sustainable management and assessment of fish stocks it is dependent upon accurate biological information about characteristics like reproductive mode, fecundity and size and age at maturity (Beer et al, 2013;Birkeland & Dayton, 2005;Brandt et al, 2017).…”