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1 November 2014 Comparison of Hatching Mode in Pelagic and Demersal Eggs of Two Closely Related Species in the Order Pleuronectiformes
Mari Kawaguchi, Kaori Sano, Norio Yoshizaki, Daisuke Shimizu, Yuichiro Fujinami, Tsutomu Noda, Shigeki Yasumasu
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Abstract

We compared several characteristics of the pelagic eggs of Verasper variegatus with those of demersal eggs of Pseudopleuronectes yokohamae, both in the order Pleuronectiformes (halibuts or flatfishes). V. variegatus eggs had about twice the diameter of P. yokohamae eggs. However, the total egg protein weight of P. yokohamae was similar to that of V. variegatus. The specific gravity of P. yokohamae eggs was calculated to be 7-fold that of V. variegatus. The difference in size is the main feature distinguishing the two types of egg. The thickness of the egg envelope of P. yokohamae— more than twice that of V. variegatus—must affect the manner of hatching. The amount of hatching enzyme synthesized in pre-hatching embryo was estimated to be larger in P. yokohamae than V. variegatus. The distribution of hatching gland cells differed between the species. In V. variegates embryos, these were located on the yolk sac as a narrow ring-shaped belt, resulting in cleavage of the egg envelope into two parts by digesting a limited region of the egg envelope, called “rim-hatching”. The hatching gland cells of P. yokohamae embryos were distributed all over the surface of the yolk sac, forming a hole through which the embryo could escape. Thus, the location of the hatching gland cells in pre-hatching embryos varied during the evolution of the Pleuronectiformes, depending on the egg type and manner of hatching.

© 2014 Zoological Society of Japan
Mari Kawaguchi, Kaori Sano, Norio Yoshizaki, Daisuke Shimizu, Yuichiro Fujinami, Tsutomu Noda, and Shigeki Yasumasu "Comparison of Hatching Mode in Pelagic and Demersal Eggs of Two Closely Related Species in the Order Pleuronectiformes," Zoological Science 31(11), 709-715, (1 November 2014). https://doi.org/10.2108/zs140018
Received: 27 January 2014; Accepted: 1 July 2014; Published: 1 November 2014
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KEYWORDS
astacin protease family
demersal egg
egg envelope
hatching enzyme
pelagic egg
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