Aspects of the reproductive cycle of Atlantic cod, Gadus morhua L., from inshore Newfoundland

Rideout, Rick M. (1999) Aspects of the reproductive cycle of Atlantic cod, Gadus morhua L., from inshore Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Data on maturity, condition and gonad histology were collected to give insight into the reproductive biology of Atlantic cod, Gadus morhua L., in Placentia and Trinity Bay, Newfoundland. Female cod in Placentia Bay spawned between April and August, with some spawning probably occurring later in the fall. Oocytes began to ripen for the next season 1-2 months after spawning with cortical alveoli appearing as early as July and exogenous vitellogenesis starting as early as August. Oocyte development continued throughout the winter. Spawning was usually determinate but the ability to boost fecundity by recruitment of oocytes into vitellogenesis during spawning was noted. Atresia of previtellogenic and vitellogenic oocytes existed as a mechanism to downgrade fecundity. -- The testes of Placentia Bay cod were filled with spermatozoa between January and August and spermiation was likely possible over most of this period. Recovery from spermiation and the subsequent advance of the testes to spermiogenesis occurred quickly, probably over 2-4 months. Spermatogenesis was completed prior to the winter reduction in feeding intensity. -- Seasonal changes in condition indices differed slightly for female and male cod from Placentia Bay. Female somatic condition factor increased from April right up until October as the fish fed and decreased throughout the winter, as oocyte development continued. The pattern was similar for males but maximum somatic condition factor was reached in August and then maintained until November, after which it decreased. Female condition and gonadosomatic index was maximum during spawning. Male gonadosomatic index was also high immediately prior to and during spawning but there were two peaks in condition factor, one during spawning and one in November at the start of spermiogenesis. -- The existence of non-reproductive cod suggests that spawning is not always annual for some individuals. In Smith Sound, Trinity Bay, over 30% of the female cod that had started to ripen were resorbing all developing oocytes by January and would have missed spawning in 1999. Spawning omission may have been triggered by food shortage during a critical period for gonad development. A small percentage of male cod had delayed gonad development but may still have been able to spawn in 1999. Data to support small percentages of cod with multiple year interruptions in oocyte development and ovarian senescence were also collected.

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