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A Method for Viewing the Germinal Vesicle in Oocytes of Commercial Catfishes
Author(s) -
Stoeckel Joseph N.
Publication year - 2000
Publication title -
north american journal of aquaculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 41
eISSN - 1548-8454
pISSN - 1522-2055
DOI - 10.1577/1548-8454(2000)062<0240:amfvtg>2.3.co;2
Subject(s) - germinal vesicle , fixative , ictalurus , catfish , biology , oocyte , clearance , andrology , anatomy , fishery , microbiology and biotechnology , embryo , fish <actinopterygii> , cytoplasm , medicine , urology
Position of the germinal vesicle is a key indicator of stage of oocyte maturation, and thus it is a valuable assessment tool in studies of the reproductive biology of fishes. The germinal vesicle of untreated oocytes of commercially reared catfish species cannot be seen because oocytes of these species are opaque. However, submerging them in a bath of Serra's fixative (ethanol, formalin, and glacial acetic acid mixed 6:3:1 by volume) effectively cleared oocytes of channel catfish Ictalurus punctatus , blue catfish I. furcatus , and flathead catfish Pylodictis olivaris collected during the spawning season and readily permitted viewing of the germinal vesicle. The time to clear oocytes that were 3.0 mm or more in diameter ranged from 16 to 30 min (mean, 24 min). Oocytes usually became opaque several minutes after they were cleared, but there was ample time to determine positions of germinal vesicles within the oocytes. Oocytes can be extracted, sealed in a vial for at least 2 h, and then cleared in the laboratory with Serra's fixative. This enhances processing efficiency because oocytes from several fish can be collected and processed simultaneously. It is also possible to secondarily clear oocytes that have been preserved in Serra's fixative for several months with follow‐up clearing procedures, thereby providing additional opportunities to evaluate the stage of oocyte maturation. However, the contrast between germinal vesicles and oocytes treated with follow‐up clearing procedures was not as good as that following initial treatment with Serra's fixative.