Int. J. Dev. Biol. 52: 753 - 757 (2008)
doi: 10.1387/ijdb.072543ta
© UPV/EHU Press

The use of poly-L-lysine to facilitate examination of sperm entry into pelagic, non-adhesive fish eggs

Tadashi Andoh1, Takahiro Matsubara1, Tatsuo Harumi2 and Ryuzo Yanagimachi*,3

1Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido, Japan, 2Department of Anatomy, Asahikawa Medical College, Asahikawa, Japan and 3Institute for Biogenesis Research, University of Hawaii Medical School, Honolulu, Hawaii, USA

ABSTRACT The fish egg is surrounded by a thick envelope called the chorion. The fertilizing spermatozoon enters the egg through a canal-like structure in the chorion, the micropyle. Examination of micropyle at fertilization is difficult if eggs are large and have no distinct landmarks surrounding the micropyle, or if they are positively buoyant in water. Eggs of many commercially important fishes (e.g., flounder, sea bream and eel) are buoyant in water or only slightly adhere to solid objects (e.g., sands, rock and water plants), which makes observation of spermatozoa at fertilization difficult. Here, we report that such eggs can be firmly attached to plastic and glass dishes that have been previously coated with poly-L-lysine. These adhering eggs can be fertilized and develop normally on the dishes. Observations of micropyles of three fish species, before and after sperm entry are presented.


fertilization, egg, sperm, micropyle, fish, poly-L-lysine

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