Notes: Abstract  The seasonal vertical migration of adult Calanus hyperboreus Krøyer and their female reproductive biology have been studied in the central Greenland Sea, based on 7-month coverage during one annual cycle. Females dwelled in surface waters only between April and July. Gonad maturation began after the summer descent into deeper waters between September and October in the absence of food. Breeding was assessed from gonad development and egg production experiments. It started around the beginning of November and was mostly completed by March/April, before the spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shallower depths. Males were mostly found during the breeding period, where they inhabited the 500- to 1000-m layer. Female dry weight was highest in August and November and lowest in February. Field observations were supplemented by observations on gonad development and egg production of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fecundity were determined at 0°C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fatter and produced up to 1000 eggs in several clutches deposited at regular intervals.

Notes: Abstract Oogenesis and gonad development ofCalamus finmarchicus during the winter spring transition in a fjord in Northern Norway were studied. A combination of observations on whole animals (macroscopic), taking advantage of their transparency, and histological sections was used to establish a system of gonad maturation stages, to describe the spawning cycle and to estimate egg production rates from preserved samples. During their development, oocytes change their shape and size, the morphology of the nucleus, and the appearance of the ooplasm. Four oocyte development stages were identified and related to a macroscopic system of four gonad developmental stages (GS) that can be applied to whole stained animals. During gonad development, the macroscopic morphological modifications of the gonads are mainly manifested in an increase in number and size of the oocytes and their distribution in diverticula and oviducts. The maturation processes during the spawning cycle (the period between egg depositions) were described from histological sections of females preserved at regular intervals after egg deposition. The macroscopic GS did not vary during the spawning cycle. This GS was a highly significant indicator for females, which spawned within 24 h after collection at 5°C. Another histological indicator for the last third of the spawning cycle is the appearance of distinct chromosomes, which, however, are only seen in histological sections. For the prediction of egg production rate of aCalanus population, in addition to the number of females spawning, knowledge of clutch size and the interval of clutch deposition is required. Clutch size was determined by counting the number of the oocyte stages to be released during the next spawning event in serial sections of the gonads. There was no significant difference in clutches laid by the females during 5 days before preservation. From the observations it seems that GS 4 predicts females that are ready to spawn within the minimum spawning interval characterisitic for a given temperature. If this holds true, it should be possible to predict in situ egg production rates solely from preserved samples.

Notes: Abstract The seasonal vertical migration of adultCalanus hyperboreus Krøyer and their female reproductive biology have been studied in the central Greenland Sea, based on 7-month coverage during one annual cycle. Females dwelled in surface waters only between April and July. Gonad maturation began after the summer descent into deeper waters between September and October in the absence of food. Breeding was assessed from gonad development and egg production experiments. It started around the beginning of November and was mostly completed by March/April, before the spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shallower depths. Males were mostly found during the breeding period, where they inhabited the 500- to 1000-m layer. Female dry weight was highest in August and November and lowest in February. Field observations were supplemented by observations on gonad development and egg production of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fecundity were determined at 0°C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fatter and produced up to 1000 eggs in several clutches deposited at regular intervals.