Pictures under white light would be needed, but I'm pretty sure this is mucus feces. This issue has multiple possible causes. Some are serious, some less so, and some aren't a problem at all. You say the female is "acting strange" also. How exactly?
Here is a write up I did on mucus feces:
Here is a write up I did on this subject:
Excess mucus in fish feces: this will present as white or light colored, stringy fecal material that often
hangs from the fish’s anus for a longer than normal period. There are a number of different causes for
this, some benign, others very serious. Without access to a microscope, there is little that can be done to
diagnose this issue effectively.
Idiopathic mucus feces: this fancy term is just to describe white mucoid bulky feces of no
serious consequence, but of an unknown cause. Some suspicion is that this can be caused by changes in
diet or diets high in fats.
Starvation: Fish that have no food moving through their bowels may excrete white mucoid feces
with little bulk to them. The primary diagnostic for this issue is evident in that the fish won’t been seen to
be eating. Resolving the anorexia is of course the prime focus to resolve this issue.
Bacterial infection: internal bacterial infections can cause stringy feces as well. While some of
these may resolve on their own, medicated foods containing a broad spectrum, gram negative oral
antibiotic may be required.
Metazoan infections: multicellular worms are often blamed for mucoid feces, but in reality, they
are almost never the root cause for this, and really, can only be diagnosed through looking for their ova in
fecal samples. Fish can harbor tapeworms and nematodes without producing mucoid feces.
Protozoan infection: Hexamita and related diplomonad flagellate protozoans very frequently
cause white stringy feces, especially in newly acquired clownfish. Metronidazole is the most frequent
treatment for this issue. It can be dosed orally at 25 mg per kg of fish body weight, or 5 g in a kg of food.
However, it is a very bitter medication, and some fish will refuse to feed on food containing it. It can be
dosed in the water at 25 mg/l, but this is more effective in treating marine fishes, as freshwater fish do not
“drink” aquarium water.
Coccidia: These microscopic, spore-forming, single-celled parasites are common diseases in
dogs and cats. In fish, they cause epithelial necrosis of the gut, enteritis and the copious production of
mucus (Noga 2010). These cannot be diagnosed without microscopic examination, and there is no well
researched cure for this in fishes, although Toltrazuril has been tested.
Constipation: This malady is often given as a cause for stringy feces, but it is not as common as
one would think. When it is seen, the feces are usually dark, not light in color. Often touted as a “cure
for constipation”, many aquarists add Epsom salts (magnesium sulfate) to the aquarium’s water – do not
do this in marine aquariums, its use is primarily as a tonic/dip for freshwater fish. Seawater formulas
already contain between 7 and 19 grams of magnesium sulfate per gallon (depending on the recipe). NSW
magnesium level is around 1200 ppm and sulfur is around 840 ppm. Some benefit might be seen using it
as a dip in additional concentrations, but adding a small amount to a marine aquarium itself has no
benefit. Epsom salts do have some possible benefit when mixed into the food as a 3% by weight adjunct.
Another commonly heard remedy for constipation is; “feed fresh peas”. This is an effective cure for
fancy goldfish and Malawi cichlids that develop constipation and bloating. Again, overextrapolation has
marine aquarists trying to feed peas to carnivorous fish, etc. The best method to enhance gut motility in
fish is to feed frozen adult brine shrimp – not as a permanent diet, just long enough to get the constipation
resolved.
Jay
