Ultrastructure of a sphaerospora sp. (myxosporida) in goldfish kidneys

Micro.. 1 9 8 0 , Vol : I I, pp. 4 9 9 . 5 0 0 Pergamon prexs Lid Printed In Grca! Britain

ULTRASTRUCTURE OF A SPHAEROSPORA SP. (MYXOSPORIDA) IN GOLDFISH KIDNEYS

R. C. HAMILTON E. M. Unit, Commonwealth Serum Laboratories, 45 Poplar Road, Parkville, Victoria 3052, Australia

During a study of "goldfish ulcer disease" in a colony of goldfish, kidneys from the goldfish were examKned by histology and electron microscopy for the presence of the bacterium which causes goldfish ulcer disease. Although no bacteria were observed, myxosporldans were present in all the kidneys examined. Dr Jirl Lom and Assoc. Prof. Louis Lelbovitz independently identified the myxosporldans as a Sphaerospora sp. The level of infection varied from fish to fish and did not correlate with the presence of ulcers on the fish. Some apparently healthy fish had numerous myxosporldans in their kidneys. However, it is possible that the presence of the myxosporldans may have been a "stressing factor" which made the colony of goldfish more susceptible to ulcers. The myxosporldans were coelozoic and appeared to infect all types of kidney tubule. There did not appear to be any obvious host reaction to them. After H&E staining the myxosporidans were readily apparent as multl-nucleated cells in the tubule lumens. The mature spores were Gram positive. While neither the invasion of the kidney nor the envelopment of the sporont was detected, the later stages of sporogenesis were observed. In the kidney tubules the enveloping cells of the myxosporidans were closely assoclated with both the mlcrov~lll and cilia (Fig. I). Short processes of the enveloping cell Interdlgltated with the tubule cell mlcrovilll, and also associated with nelghbourlng enveloping cells. Kidney cell cilia were closely applied to the myxosporldan enveloping cells. Early stages of sporogenesis consisting of an enveloping cell surrounding an undifferentiated cell, and an enveloping cell surrounding four relatively undifferentiated cells were observed. The next stage consisted of an enveloping cell surrounding cells which were partially differentiated and positioned. Each enveloping cell contained the precursors of two spores (Fig. 2). These consisted of two valvogenlc cells surrounding two capsulogenlc and two sporoplasmogenlc cells. Within each capsulogenlc cell was a polar capsule precursor which consisted of a sphere and a tubule of precursor material. Both the sphere and tubule had an electron dense core and the tubule was surroLmded by an array of mlcrotubules. The polar capsule precursor involuted to become the polar capsule (Fig. 3). The mature intracellular capsules condensing and two mature intracellular surrounding two capsular polar capsule contained

spore developed by the valvogenic cells condensing, the polar all the cells positioning themselves. The enveloping cell surrounded spores. Each mature spore (Fig. 4) consisted of two valves cells, each containing a polar capsule, and two sporoplasms. The four or five coils of the polar filament.

499

500

R.C. Hamilton

-0w~-

rig. I.

Kidney tubule infected with

Sphaerospora

s_~.

+y

Fig. 2. E n v e l o p i n g cell s u r r o u n d i n g capsulogenic cells. B a r = 1 ~m.

Bar = 2 urn.

iI

I

'

,+,

,

•

~+~

'....

. . . . Fig.

~ 3.

Polar

capsule.

Bar

= 1 urn.

.2 l:ig.

4.

Mature Bar

intracetlular =

1

urn.

spore.

two