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We discuss the use of stereology in fisheries research and by presenting novel data, along with comparisons to conventional methodology, further confirm the effectiveness of a point-counting method that estimates the relative distributions of oocyte developmental stages within an asynchronous ovary. Point-counting methodology was applied in three experiments involving the ovaries of Tilapia zillii (Gervais), a teleost that exhibits highly asynchronous ovarian development. Quantitative data were first obtained from conventional digestion of ovarian tissue with mercury-based Gilson's Fluid and compared to that derived from stereology. Analysis of covariance demonstrated no significant difference (P≥ 0.05) between counts of discrete oocyte developmental stages determined by either method. However, counts of post-ovulatory follicles (POFs) using Gilson analysis were not possible, due to the highly irregular size and shape of these structures. A second experiment compared an immediately post-spawned ovary with an ovary 5 days after spawning, presenting comparative data determined by stereology and Gilson digestion; on this occasion, Gilson analysis significantly underestimated the proportion of atretic ooytes (P < 0.05). A further experiment forms a preliminary investigation of the effect of intra-muscular injections of human chorionic gonadotropin (hCG) upon early ovarian recrudescence and is presented as an example to demonstrate the highly informative nature of stereological analysis; injections of hCG on 3 days after spawning resulted in a significant decrease of stage 5 (early vitellogenic) but significant increase of stage 6 (late vitellogenic/maturing) oocytes by day 5. We conclude that point-counting stereology is a powerful technique for the quantitative analysis of ovarian development. Moreover, stereology avoids the prolonged use of dangerous mercury-based solutions and classifies oocytes into discrete developmental stages using a combination of criteria (biochemical, histological and size distribution) and not simply oocyte size. © 2002 Elsevier Science B.V. All rights reserved.

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383 - 401