Abstract:Ovary histology of anchovy Engraulis japonicus in the Yellow Sea was studied using macroscopic and microscopic observation with olefin slices. Macroscopic characteristics of the ovary at different development stages were described; oocyte development phase composition, oocyte size distribution and the developmental differences between the two lobes of the ovary and that among the anterior, middle and posterior part of each lobe were statistically analyzed. The results showed that oocytes of different development phases were present simultaneously in the same ovary. Stage Ⅱ ovary is comprised of phase 1-3 oocytes, with phase 2 oocytes being the dominant in number (66.3%). Stage Ⅲ, stage Ⅳ and stage Ⅵ ovaries were comprised of phase 1-4 oocytes; the distinction among the ovaries at these three stages lied in the number percentage of phase 4 oocytes, which was the highest in stage Ⅳ (34.8%), second in stage Ⅲ (28.6%) and the lowest in stage Ⅵ (17.8%) ovary. Stage Ⅴ ovary was comprised of phase 1-5 oocytes, of which the quantity of mature phase 5 oocytes was the highest (29.8%). During the ovary development from stage Ⅲ to Ⅴ, it was mainly the phase 3-4 oocytes that developing towards phase 4-5, while the percentages of phase 1 and 2 oocytes remained roughly unchanged. The oocyte size distributions were characterized by distinct crests and troughs, which was contrary to the previous “shallow saw like distribution” understanding of the issue. The size (major axis) of the oocytes in stage Ⅲ and Ⅵ ovaries was of unimodal distribution, with a mode at 0.5-0.6 mm class for both stages. The oocyte size distribution was of bimodal for stage Ⅳ and Ⅴ ovaries, with the two modes at 0.2-0.3 mm and 0.7-0.8 mm, 0.5-0.6 mm and 1.1-1.2 mm, respectively. The two dominant size groups of oocytes in the stage Ⅴ ovary were well separated with a clear hiatus, and the oocytes in the larger size group were all hydrated, which were in accordance with the characteristics of batch spawners. The two lobes of the ovary were significantly different in size, with the right one being the smaller. The mean of the right/left lobe weight ratio was 0.71, with a 95% confidence interval of (0.67, 0.75). Statistical test showed that the development status of the oocytes was not significantly different (P>0.05) either within or between the two lobes.
