Table 1 Explanation of the gametogenic scale and the use of descriptive terms (primer column: present study; second column: after Christiansen 1971), utilized in scoring histological analysis of gonad tissue to assess the gametogenic stages of M. mactroides

Sexual rest

0

Sexual rest

A total absence of gametes, making it impossible to distinguish between sexes, empty follicles are observed

Active

I

Early active stage

Follicles few and small, sex distinguishable, protogonia and gonia in mitosis

a

II

Late active stage

Follicle size increases, spermatogonia and spermatocytes in males, oogonia and previtellogenic oocytes in females

b

Ripe

III

Early ripe stage

Follicle size increases and occupies the entire tissue, germinal cells in all phases of gametogenesis

c

IV

Ripe stage

Polygonal follicles almost full of ripe gametes, spermatozoa occupy most of follicle, free ripe polygonal oocytes in the lumen

d and e

Spawning

V

Partially spawned stage

Gonoducts with mature gametes in emission. Spermatozoa lose radial disposition. Free ripe rounded oocytes in the lumen and empty spaces

f

VI

Spent stage

Follicles small and practically empty, residual gametes degrading

g

Cytolysed

VII

Recovery stage

Gonadal follicles at this stage are empty, except for residual gametes, amoebocytes are present within the follicles, close to the walls and in the centre

h