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INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VOL. XXIX, PART I
Stage I (immature condition) : The ovaries are flat transparent elongated bodies present-
ing a granulated appearance after fixation. In many, remnants of the atretic follicles (corpora
lutea) belonging to the previous crop of oocyte are seen as prominent yellow patches. Fishes
with Stage I ovary are in abundance during the later part of November to January.
Stage II (slightly enlarged condition) : The ovaries lose their transparency and an yellowish
tint appears for the first time. Slight over-all enlargement is in evidence. Specimens with Stage
II ovaries are collected during February to early part of April.
Stage III (greatly enlarged condition) : The ovaries are yellowish and opaque with a granular
surface. A pronounced enlargement of them is noticeable. Stage III ovary is present in fish
collected during April to June.
Stage IV (spawning condition) : The ovaries are bright yellow with a greenish tinge and
are fully swollen with mature eggs. The ovary reaches this condition during July to September,
when a little pressure on the abdomen releases the eggs.
Stage V (partly spent condition) : The ovaries resemble those of Stage IV, but are devoid
of turgidity and become flabby. These occur in specimens collected during September and
occasionally in October.
Stage VI (completely spent, regressive condition) : The ovaries present a transitional flabby
nature, but soon they regain their compactness. This type of ovary is encountered in speci-
mens collected during October and November.
Seasonal histological changes in the ovary
Stage I : In the ovary, the oocytes of varying size are arranged in the ovigerous lamellae
which protrude into the ovocoel. The lamellae are closely arranged and the ovocoel is not
extensive (Plate I, Fig. 1). The diameter of the oocytes ranges from 4 to 175 µ, but smallest
recognizable oocytes are arranged as nests close to the lamellar wall (Plate I, Fig. 2). These
oocytes have prominent round nucleus with a solitary, median and deep staining nucleolus.
The cytoplasm is very little and completely lacks affinity for stain. These have a resemb-
lance to the resting oocytes of the immature hake [Hickling 1935]. The larger oocytes are the
Stage I oocytes; their cytoplasm is deeply stained and the nucleoli vary from one to many and
generally occupy a position beneath the nuclear membrane as in Fundulus heteroclitus, [Matt-
hews, 1938], Huro salmoides and Lepomis macrochirus [James, 1946]. Scattered distribution of
nucleoli inside the nucleus is also not uncommon. In the cytoplasm of these growing oocytes
deeply staining, solitary, round, yolk-nucleus of 12 to 16 µ diameter is observed frequently. These
resemble those described in the teleostean oocytes by earlier workers [Cunningham, 1897;
Wheeler, 1924 and Mendoza, 1943]. Among the oocytes the remnants of the atretic follicles
(corpora lutea) are seen as granular yellow pigment masses (Plate I, Fig. 3). Such bodies of
irregular shape and structure have been recorded by Cunningham [1897] as the most cons-
picuous characteristic of the spent ovary.
Stage II : During this stage, Stage II oocytes can be recognized. These are characterised
by the appearance of cytoplasmic vacuoles (Plate I, Fig. 4). Initially these vacuoles are peri-
pheral in their disposition. Some of them are filled with eosinophilic homogeneous substance
which may be homologous to the intravesicular yolk of Fundulus heteroclitus [Marza et al. 1937].
Vacuoles are scattered in the cytoplasm, of which many lack their contents during the
next stage in vacuolisation. A steady increase in the diameter of the oocytes is obvious. During
March, the larger ones have an average diameter of 216 µ. The vitelline membrane can be
easily made out. The follicular layer appears in the form of few spindle-shaped cells closely
adhering to the vitelline membrane.
Stage III : Stage III oocytes are identified by marked increase in diameter with yolk
granules deposited in their cytoplasm. In the beginning the yolk deposition is restricted only to
the periphery (Plate I, Fig. 5) but after the formation of a peripheral yolk ring, deposition
towards the interior takes place. During this stage some oocytes abort and are found in the
process of resorption,