Adrian.
A history of intermittent deaths of Rainbowfishes displaying similar
symptoms over a period of time prompted me to have a number of specimens
undergo a series of pathology tests. Condensed results and general
discussion follows.
History:
I have been having problems with a number of Rainbowfishes dying of unknown
causes over a period of years. The main species that suffered from this
problem was the Goyder River Rainbowfish. Although I have had some other
species suffer from the same symptoms, the ratio of Goyder River to other
species was staggering. I have had other specimens affected but they were
also mainly Trifasciata species. Usually only one or two fish at any one
time were affected. However, this past summer, I lost around a dozen adult
specimens of the Goyder River Rainbowfish within a period of about 8-12
weeks. I then decide to have the surviving three Goyder River specimens
examined by a qualified veterinary practitioner to see if the cause could be
established.
The symptoms presented itself as signs of patchy darkening of the skin
around the head, inappetance, isolation from the rest of the aquarium
community, surface swimming and increased respiration. Death usually
followed somewhere from 1 or 2 days to 2 or 3 weeks. In some cases this
period may have been even longer as I had found from previous experience
that all specimens suffering these symptoms eventually die, so I would
short-circuit the prolonged death by disposed of them before they actually
die. I was particularly concerned that they may be suffering from
tuberculosis and thought it better to dispose of them rather than risk
further contamination of the aquarium and other residents.
I collected the three remaining specimens and gave them to Dr. Stephen B.
Pyecroft (BVSc Hons.) for examination. The fish came from a 650 litre
aquarium containing a mixture of Australian and New Guinea Rainbowfishes.
Gross pathology results showed that all fish were in good to fat condition.
All showed signs of generalised oedema, behavioural signs as above, and
sectional darkening of the skin over random areas of the body. Body surface
signs: Oedematous epidermis with scale loss. However, no pathogens were
found on the skin scraping examined. Fins were normal and gills were pale in
colour.
Post-mortem results showed that the liver was grossly enlarged and contained
fat globules (hepatic cells examined were full of these fat globules).
Spleen was small and revealed a reduction in heamopoetic tissue. Kidneys
were oedematous and enlarged. Purulent material was present in distinct
cyst-like structures. Wet prep. revealed a loss of parenchymal tissue and
many vesicles were filled with purulent material. These varying in shape and
size. The peritoneal cavity was filled with a clear effusion. The heart was
enlarged and had a granulated appearance over all myocardium. The
pericardial sac enlarged due to the presence of a clear pericardial
effusion. One fish had discrete areas of purulent material present within
the cranium. Air dried smears were prepared from kidney tissue from the
examined fish and stained with Ziel-Neilson stain (acid-fast stain). Only
one of the tissue preparations was positive for acid-fast bacteria. The most
likely bacteria type that would exhibit this staining characteristic would
be Mycobacterium.
Although Mycobacterium bacteria was found in one specimen, it was general
concluded that this was most likely a secondary infection. However, all
three specimens showed hepatic lipodosis possibly due to nutritional imbalance.
Discussion:
Often investigations of this type produce more questions than answers. After
looking at the diet of these fish, the picture is still not clear as to the
cause of the lipodosis. I have bred and raised these fish and know exactly
what food has composed their diet from birth to death. Upon hatching they
were fed newly hatched brine shrimp nauplii, microworm and dry powered food
(Sera micron & OSI microfood). When they were large enough to take other
food they were primarily fed a home-made diet consisting of NZ Whitebait
(fish) 20%, Prawns (Shrimp) 40%, Mussels 20%, Frozen Spinach 10% and Beef
Liver 10%. All ingredients were finely ground and set with gelatine. In
addition to this, their diet was supplemented with frozen bloodworms and a
granulated pellet imported from Taiwan. The ingredients of the pellet food
is stated to be fish protein, white fish meal, wheat germ, dried yeast,
wheat flour, soybean meal, shrimp paste, mineral and vitamins. In what
proportions is not stated. Analysis showed crude protein 46% min., crude fat
4% min., crude ash 16% min., and moisture 9% max. Growing fry were fed
twice a day and sub-adult and adults fed once per day.
Their diet consisted of about 80% home-made food and 20% pellets and
bloodworms. However, for the last 12 months of their lives this percentage
changed, and the pellets basically replaced the home-made food. Mainly
because I found that these pellets were readily accepted by the fish and the
costs were reduced. The pellet diet was continued to be supplemented with
the bloodworms and home-made food.
Some authorities feel excess carbohydrates and fat in fish foods can be
harmful to many species and fatty degeneration has been reported in a number
of fish including Characins and labyrinth fish. However, such fatty
degeneration considered as a pathological change and attributed to certain
types of foods may not be caused by the food ingredients but by the volume
of food fed. It was generally agreed that the above diet fed to the
Rainbowfishes seemed adequate and reasonably well-balanced and it may just
be a case of feeding too much. I must admit that I probably do feed a bit
heavy - perhaps a carry-over from my Cichlid keeping days. However, perhaps
there is another explanation. When we look at it there is very little known
about the dietary habits of Rainbowfishes in the wild. It may well be that
Rainbowfishes and other tropical fishes for that matter, feed heavy during
the wet season when food is abundant and store any excess consumed to carry
them through the dry season when food items are scarce. In other words,
Rainbowfishes may have the ability to store excess proteins and fats in
their body tissue rather than just passing it out. If we then maintain these
fishes into the aquarium and feed them every day, then they will just store
the excess causing lipodosis and eventually death.
All this is of course only conjecture, but in the absence of other hard data
it could be a possibility. Also, to add to this mystery, I have another 15
Goyder River Trifasciatas in a 450 litre aquarium from the same brood and
have not lost one specimen from that tank. These fish are the same age, size
(if not bigger) and have been fed the very same diet as the other fish. They
were separated about 8-12 months ago and share their aquarium with some
Ambassis.
I would be pleased to hear any suggestions, solutions or alternative
theories. I for one will be drastically reducing the amount of food fed to
my fishes.
........................................
Adrian R. Tappin
Home of the Rainbowfish
http://www.ecn.net.au/~atappin/home.htm
........................................