Gametogenesis in the Capelin, Mallotus villosus (Müller) from the Northwest Atlantic

• Main Author: Flynn, Shawn R.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1996
• Subjects: Huxley; Northwest Atlantic
• Online Access: https://research.library.mun.ca/4160/; https://research.library.mun.ca/4160/1/Flynn_ShawnR.pdf; https://research.library.mun.ca/4160/3/Flynn_ShawnR.pdf

Capelin, Mallotus villosus (Muller), from the Northwest Atlantic were examined to describe the anatomical structure of the gonads and their positioning in the body cavity in relation to that of other fish. The testes of immature fish were thread-like, elongate, smooth and clear without obvious internal divisions in histological cross section. Those of maturing fish were elongate and smooth but much more robust, flattened and white. -- In maturing fish the final stages of spermatogenesis begin in the Fall of the year before spawning and are easily recognized as primary spermatogonia begin a process of division. This results in the division of the testes into lobules containing cysts. Within the cysts cells develop synchronously but the development of cells from different cysts is asynchronous. Sperm cells first appear in October and as development continues cysts filled with sperm break down and form larger pools of sperm starting in February. Fish examined immediately after spawning had gonads that were distended and contained only small amounts of residual sperm. -- The ovarian anatomy is unusual in that ovarian wall covers only the medial half of the organ and the oocytes develop in lamellae that extend freely into the body cavity. This type of ovarian structure was previously described by Brock, 1878 and Huxley, 1883. -- Four potential year classes of oocytes develop in the capelin ovary simultaneously and can be distinguished on the basis of size and cytological character. In immature fish all four are previtellogenic, but in maturing fish the fourth year class begins vitellogenic growth during the fall (September - October) of the year prior to spawning. This year class will mature over the winter passing through several developmental phases until final ovulation in June - August Mature eggs are ovulated directly into the body cavity and spawned through the gonopore located just posterior to the anus. The previtellogenic stages continue to develop during this time but at a slower rate. Their slight increase ...