Abstract
Polar cod (Boreogadus saida) is considered a key species in the Arctic marine ecosystems. Yet detailed or even basic knowledge regarding its biology and adaptations, especially during the polar night, is in many cases poor. Data are presently unavailable in Western literature on the gonad development of polar cod and its reproductive biology in wild specimens. Accordingly, gonad development of wild-caught polar cod from fjords of the Svalbard archipelago was studied across seasons (April, August, September, November and January). Histological analyses of polar cod showed strong indication of a group-synchronous oocyte development with determinate fecundity and iteroparity. Females started gonadal development prior to April and had not yet reached the final stage of maturation in January. Testes matured more rapidly, with males ready to spawn in January. Furthermore, our data show that polar cod were able to reach sexual maturity at age 1+. Based on our data and previous reports, we hypothesise that polar cod is a total spawner.
Highlights
Polar cod (Boreogadus saida) is a circum-Arctic species common in both open and ice-covered waters of the Arctic shelf seas (Ponomarenko 1968; Rass 1968; Craig et al 1982)
In August and September (Fig. 1c, d), the eight analysed female specimens were at a similar stage of oocyte development as the developing individuals sampled in April, with more than 30 % of the oocytes being in the cortical alveoli stage oocyte (CA) stage and 30 % (August specimens) in the Vtg1 stage (Table 2)
The oocytes at the CA stage (202 ± 6 lm) showed a significantly increased diameter compared to the primary growth oocyte (PG) oocytes (79 ± 4 lm) (Fig. 1c)
Summary
Polar cod (Boreogadus saida) is a circum-Arctic species common in both open and ice-covered waters of the Arctic shelf seas (Ponomarenko 1968; Rass 1968; Craig et al 1982). Limited access to field data during the polar night, has hindered comprehensive and holistic studies of the reproductive biology and development of polar cod (see Berge et al 2015 for a review). Most of the existing knowledge on polar cod reproductive biology has been obtained from studies carried out on captive fish (Graham and Hop 1995; Sakurai et al 1998) including experimental data on spawning energetics and fecundity estimates (Hop et al 1995), egg characteristics (Andriyashev 1954; Graham and Hop 1995; Ponomarenko 2000) and optimal conditions for spawning (Altukhov 1979; Lapin and Matzuk 1981) and embryonic development (Doroshev and Aronovich 1974; Aronovich et al 1975; Sakurai et al (1998)).
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