Table 1.
Criteria used for staging G. holbrooki embryos.
Fig 1.
(a) Gravid spot of a female G. holbrooki with high intensity value (less dark). The yellowish colour of the yolk/eggs can be seen when observed under dissecting microscope. (B) Embryo’s eyes at final developmental stage are visible through the gravid spot (red arrows). (C) Black pigment is scattered over the sac but is concentrated on the posterior margin of the ovarian sac. (D) Area of the skin corresponding to the gravid spot (circled red) appears as a translucent window after the ovarian sac was removed from the body cavity. Dorsal to the top and anterior to the left.
Table 2.
Number of G. holbrooki females with overlapping developmental stages.
Fig 2.
Panel showing mature eggs and embryos of G. holbrooki at various developmental stages.
(A) Mature unfertilized eggs with no sign of cell division; (B) Stage I embryos with rudimentary optic cupules/eyes (arrow); (C) Stage II embryo with anterior neural tube broadened (arrow); (D) Stage III embryo with eye pigmentation prominent (arrow) and visible vitteline veins (arrow head); (E) Stage IV embryo with fine capillaries on the surface of the pericardial sac (arrow), melanophores on the tail (arrow head) and visible gill slits and (F) Embryo at late developmental stage (Stage V), showing the caudal fin rays (arrow). At this stage the mouth and nostrils are also visible through the pericardial sac [17].
Fig 3.
Dissected ovarian sac of two G. holbrooki females showing embryos at multiple stages of development suggesting superfetation.
(A). A developed (stage IV; arrow) as well as an early stage (stage II; arrow head) embryo alongside mature unfertilized eggs (asterisk). (B) Stage II (arrow) and stage I embryos (inset) together with mature unfertilized eggs (asterisk).
Fig 4.
Range of gravid spot intensity values corresponding to fish with assigned embryonic stages of development. As fish carried more than one developmental stage (generally 2) they assigned to the most dominant developmental stage they carried.
Fig 5.
Relationship between (A) gravid spot intensity and female size (total length); (B) gravid spot intensity and fecundity; (C) fecundity and female size (total length); (D) female size (total length) and gravid spot size; (E) gravid spot intensity and gravid spot size and (F) fecundity and gravid spot size.
Note: Higher and lower intensity values represent lighter and darker coloration respectively.
Fig 6.
Gestation period of G. holbrooki at two different rearing temperatures.
Fig 7.
Frequency of parturition timing (left) and postures (right) in G. holbrooki at: (A) 25°C and (B) 23°C.
Fig 8.
Panel summarizing the parturition process in G. holbrooki.
(A) Most frequently observed “tail-first” parturition event where tail of the fry (red arrow) emerged first from the genital pore; (B) Infrequent ‘head-first’ parturition event where the head (arrow head) of a fry emerged first from the genital pore. In this example, note the tail (red arrow) of the next fry born emerged before the one ahead was completely released; (C) On few occasions ‘twin births’ where two fries could be seen emerging simultaneously out of the genital pore (red arrow); (D) Parturition event showing a fry being born with yolk (asterisk) still intact. Note, the free tail (arrow) with head still stuck in the ovarian sac; (E) A safely born fry with the yolk sac (asterisk) still intact. Also see S1 Video.