OBSERVATIONS ON THE REPRODUCTION OF THE SPINY DOGFISH, SQUALUS ACANTHIAS

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Abstract
S. acanthias of the Atlantic coast migrates northward in the spring and southward in the fall. The fish are present at Woods Hole, Massachusetts, from late April to early June and again in Oct. and Nov. The adult [female][female], when they appear in the spring, have uterine young which are either early embryos enclosed in membranous capsules ("candles") or more advanced "pups" 12-20 cm. long, with large pendent yolk sacs, and free in the uterine lumen. Adult [female][female] ,when seen in the fall, have candle embryos 3.5-7.5 cm. long or large pups 25-29 cm. long, whose yolk sacs are greatly reduced or completely absorbed, while a few [female][female] have given birth to their young. Thus 4 distinct stages of gestation are seen when the fish are divided on the basis of development of uterine young. The gestation period apparently covers about 20-22 months and a [female] gives birth every other year. This opinion is supported by the progressive advancement in development of the young in the 4 stages of pregnancy. Also, correlated with this is a gradual involution of the corpora lutea and a corresponding increase in size of the ovarian ova which will be ovulated following the conclusion of the existing pregnancy. Analysis of candle ova and pups of the 4 stages of gestation show an increase in water and a decrease in both organic and inorganic matter as indicated by dry weights and content of ash. Thus it seems that gestation in the spiny dogfish should be considered as being ovoviviparous.

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