Gonadal differentiation in Atlantic cod, <I>Gadus morhua</I> L., and haddock, <I>Melanogrammus aeglefinus</I> (L.)

Abstract

. 2008. Gonadal differentiation in Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus (L.). Acta Ichthyol. Piscat. 38 (2): 127-133.Background. The purpose of this study was to determine the timing of gonadal differentiation in two gadoids: Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus (L.). This information is required to develop a practical protocol for the production of monosex populations of these species for aquaculture. Materials and Methods. Cultured larvae and juveniles were collected weekly, measured (total length; TL), prepared histologically and then examined microscopically for the presence of characteristic stages of gonadal differentiation. Results. In Atlantic cod, undifferentiated gonads were present by 18 mm TL, at 84 days post hatch (dph), and definitive germ cells by 19 mm TL (90 dph). Ovarian cavities were first observed at 27 mm TL (102 dph), and by 35 mm TL (112 dph) anatomical divergence into two types of gonads was clear. In haddock, undifferentiated gonads were observed at 21 mm TL (64 dph) and an ovarian cavity was evident at 29 mm TL (71 dph). Conclusion. Gonadal differentiation in Atlantic cod and haddock occurs at roughly the same size in both species (27 and 29 mm TL, respectively). For successful sex reversal, the administration of steroids should therefore begin at approximately 25 mm TL, shortly after weaning onto dry feed.

Sex differentiation in Atlantic cod (Gadus morhua L.): morphological and gene expression studies

“…Our study provides evidence that morphological gonad differentiation in Atlantic cod occurs earlier in females than in males, as generally found in other primary gonochoristic teleosts [ 5 , 9 ]. Different from the results presented here, an earlier report described ovarian cavity formation in Atlantic cod at 27 mm TL [ 42 ]. This divergence might be related to significant growth differences between the two studies.…”

“…Our results confirmed that Atlantic cod is a differentiated gonochoristic species, where the sexually undifferentiated gonad develops directly into a testis or an ovary [42]. Our study provides evidence that morphological gonad differentiation in Atlantic cod occurs earlier in females than in males, as generally found in other primary gonochoristic teleosts [5,9].…”

“…A phylogenetic analysis of teleost sox9 sequences deposited in the NCBI databank together with Atlantic cod sequences ( Additional file 3 : Figure S3) obtained from the recent genome sequence [ 56 ], revealed two subtypes that both are clearly distinct from sox8 , similar to the situation in other teleosts such as zebrafish [ 39 ], medaka [ 42 ] and rainbow trout [ 43 ]. The Atlantic cod sox9 transcript studied in this communication is a sox9b variant, although the classification is somewhat unclear due to variable naming among the databank entries.…”

“…Based on morphological studies, sex differentiation in Atlantic cod was initially reported to take place from approximately 27 mm total body length (TL) [ 42 ], and steroid treatment to induce masculinization was recommended from approximately 25 mm TL. But a more recent study demonstrated that exposure of Atlantic cod to 17-α-methyltestosterone in the diet from 12 mm to 25 mm TL onwards resulted in high proportion of hermaphrodites, suggesting that sex differentiation commenced earlier than at 27 mm TL [ 2 ].…”

Ontogenesis of gonadal aromatase gene expression in atlantic silverside (Menidia menidia) Populations with genetic and temperature‐dependent sex determination

“…The timing of gonad development is a highly labile process both within (Maack et al, 2003;Melia et al, 2006;Wang et al, 2007) and among species (Devlin and Nagahama, 2002;Chiasson et al, 2008). Plasticity in the timing of gonad differentiation may be owing to differences among strains (e.g.…”