The reproductive cycle of female Ballan wrasse Labrus bergylta in high latitude, temperate waters

A new experimental model for the investigation of sequential hermaphroditism

The stunning sexual transformation commonly triggered by age, size or social context in some fishes is one of the best examples of phenotypic plasticity thus far described. To date our understanding of this process is dominated by studies on a handful of subtropical and tropical teleosts, often in wild settings. Here we have established the protogynous New Zealand spotty wrasse, Notolabrus celidotus, as a temperate model for the experimental investigation of sex change. Captive fish were induced to change sex using aromatase inhibition or manipulation of social groups. Complete female-to-male transition occurred over 60 days in both cases and time-series sampling was used to quantify changes in hormone production, gene expression and gonadal cellular anatomy. Early-stage decreases in plasma 17β-estradiol (E2) concentrations or gonadal aromatase (cyp19a1a) expression were not detected in spotty wrasse, despite these being commonly associated with the onset of sex change in subtropical and tropical protogynous (female-to-male) hermaphrodites. In contrast, expression of the masculinising factor amh (anti-Müllerian hormone) increased during early sex change, implying a potential role as a proximate trigger for masculinisation. Collectively, these data provide a foundation for the spotty wrasse as a temperate teleost model to study sex change and cell fate in vertebrates.

Isolation, identification and characterisation of ballan wrasse Labrus bergylta plasma pigment

This study confirmed that observations of blue-green colouration in plasma fractions of the ballan wrasse Labrus bergylta were caused by the linear tetra-pyrrole biliverdin and that the molecule was of the physiologically relevant IXα isomer. Accumulation appears driven by chromogenic association with an unknown protein moiety which precludes enzymatic reduction and would suggest active management. It was demonstrated that the pigment did not fluctuate relative to ontogeny, or indeed binary gender in the species of interest, but mobilisation and depletion in the subset of individuals undergoing sex change at the time of study supports a potential association with gender inversion processes. It is of note that although biliverdin does have some effect on external colouration, the evidence is indicative that crypsis is a supplementary function thus other factors must be considered.

Gender distribution, sexual size dimorphism and morphometric sexing in ballan wrasse Labrus bergylta

In wild ballan wrasse Labrus bergylta, mass-length relationships were not different between genders, and positive allometry was found in the mixed-gender population. Male-biased sexual size dimorphism was significant and the most effective morphometric method for sexing L. bergylta outside of the species spawning window used body mass (M(B) in g), total body length (L(T) in mm) and Fulton's condition factor (K) as discriminant variables to predict gender with 91% accuracy. The discriminant score (S(D)) of a specimen can be calculated as S(D)  = 0.01 M(B)- 0.016 L(T)- 3.835 K + 6.252 to predict its gender as female or male if S(D) is < 1.459 or S(D) is > 1.504, respectively. There was a potential trend towards earlier sexual inversion compared to previous studies at comparable latitudes. Sex change is a phenotypically plastic trait under social control in haremic fishes and should be monitored in increasingly exploited L. bergylta.