Reproductive Cycle, Spawning, and Fecundity of Sebastes oculatus (Patagonian Redfish) in the Argentine Continental Shelf
The Patagonian Redfish (Sebastes oculatus) is a viviparous species that inhabits the mid and outer shelf waters and rocky reefs off the Patagonian coast of Argentina where two morphotypes have been identified: the “dark” or “shallow” (mostly <30 m depth) and the “light” or “deep” (>80 m depth). Information on the reproductive biology of the “light” morphotype is scarce, so the main objectives are to describe the gonadal maturation phases and to determine the oocyte growth pattern of the species in deeper waters. In addition, we analyze the annual cycle of gonadal and liver condition indices in relation to sexual maturity and provide a preliminary estimate of potential fecundity. Samples were collected on commercial vessels by on-board observers between November 2016 and October 2017. The pattern of oocyte development showed that S. oculatus is a group-synchronous species, with gonad development beginning in the late austral winter and continuing into the spring, while larval emergence occurs in spring and early summer. Males mature before females, so copulation may occur in the fall, and females would retain sperm in the ovary until oocyte fertilization. The evidence suggests that viviparity of this species is lecithotrophic, and positive relationships have been found between relative fecundity with maternal size, which indicate that larger and older females have greater reproductive potential (producing more eggs than younger individuals).
Location of sampling stations where specimens of Sebastes oculatus were captured between November 2016 and October 2017.
Cross-sections of ovaries of S. oculatus at different phases of maturation. (A) Immature: with previtellogenic oocytes (PV), characterized by small size and strongly basophilic cytoplasm. The nucleus is central and the nucleus/cytoplasmic ratio (N:C) is about 0.5. (B) Developing: the oocytes incorporate the yolk synthesized in the liver in the form of globules (Y). Some transparent lipid vesicles (LV) were observed around the nucleus. (C) Larva with pigmented eye (E) inside the egg in the spawning-capable ovary phase. Remnants of yolk (Y) were observed. (D) Higher magnification of Figure 2C, showing part of the larva (L) and vitellogenic oocytes in beginning of atresia (AT). (E) Regressing phase, with post-ovulatory follicles (POF) and atretic oocytes (AT). (F) Regenerating: with previtellogenic (PV) and some atretic oocytes (AT).
Photomicrographs of testicular histology of S. oculatus at different phases of maturation. (A) Developing: Spermatocytes I (SCI) are spherical, about 5 µm, and they have a basophilic nucleus. Spermatocytes II (SCII) are similar but smaller, about 2.5 µm. Spermatids (SD) are less than 2 µm. Spermatozoa (S) have a flattened conical head that is 2.5 µm long. (B) Spawning capable: sperm ducts filled with spermatozoa (S). (C) Regressing: residual spermatozoa (S) present in the lumen of the ducts. The lumen of the ducts is greatly enlarged. Cells in different stages of spermatogenesis are not observed. (D) Regenerating: almost empty cysts with remnants of spermatozoa (S).
Percentage of mature females of S. oculatus at different phases of the reproductive cycle (November 2016–October 2017).
Percentage of mature males of S. oculatus at different phases of the reproductive cycle (November 2016–October 2017).
Gonadosomatic index (GSI) of males and females (± standard error) of Patagonian Redfish during an annual cycle.
Hepatosomatic index (HSI) of females and males (± standard error) of Patagonian Redfish during an annual cycle.
Oocyte size frequency distributions of ovaries of three female S. oculatus in the developing phase sampled in October and November (without larvae) and in the spawning-capable phase (with larvae) in November.
Dry weight (DW) of recently ovulated vitellogenic oocytes (gray circle) and free larvae (black triangle) inside the ovary of female S. oculatus as a function of total length.
Potential and relative fecundity of Patagonian Redfish as a function of total length and total weight (excluding ovaries) of females.
Contributor Notes
Associate Editor: M. T. Craig