When you create a picture of an aquarium in your mind, most likely it
will be tranquil and serene. After all, most aquarium enthusiasts
maintain an aquarium precisely to have a beautiful and inspirational bit
of nature indoors– a source of passive beauty. This of course is
accomplished by having a mix of fish that are compatible with each
other. If you have a freshwater aquarium you must be versed in the
temperament of aggressive freshwater fish species in order to keep the
peace.
Before we look at the most common species known for their harsh
temperament, it must be prefaced with the following. All fish will be
aggressive and all fish will be passive. This may sound like a
contradictory statement, but it is essentially a law of nature. Until
one starts keeping great white sharks in a home aquarium, every species
that you will have in your aquarium will be both a predator and prey of
other species in nature. Yes, even your plant eaters prey on plants!
Being aware of this natural occurrence will help you in avoiding Wild
West style saloon fights, „fish-style.”
Now, who are the toughest of the tough… the meanest of the mean in aquarium freshwater fish?
Red Bellied Piranha
When it comes to aggressive freshwater fish, you cannot get more
aggressive than the red belly piranha. They can make for great
aquarium fish when kept with others of their own kind. They are large, growing as
big as 12 inches and will eat fish smaller than them, so contemplating
an introduction of red belly piranha into a cross-species tank would be a
mistake.
Siamese Fighting Fish
This is the species most commonly labeled as an aggressive freshwater
fish. This reputation is well deserved, but it should be tempered
slightly. First, male Siamese fighting fish, or Betta fish as they are
also known, are very aggressive. If two males are placed in the
same tank they will fight to the death. This is how they establish
mating and feeding territories in nature. Obviously, you would want to
avoid this situation. Female Betta fish do not display this behavior and
can live communally.
Male Bettas could be placed in a tank inhabited by other species, but
even here caution should be taken. If your other fish display long wavy
appendages similar to a Betta or if the tank is crowded, fights could
break out which can be deadly for other less aggressive species.
Angelfish
Do not let their common name fool you. These cichilds can be as
aggressive as they are beautiful. They can coexist in a tank with tetras
fairly well, as the tetra is rather docile with the angelfish and the
angelfish’s mouth does accommodate a tetra to well for biting or killing
purposes. Guppies, however, do not generally mix well with angelfish.
The guppy has a tendency to nip at the angelfish’s extended fins and due
to their small size, often resulting in seriously injured or dead
guppies by the mouth of an angelfish.
A good rule of thumb with angelfish is to avoid placing them with
smaller species. When new fish are introduced into an aquarium
environment with angelfish present, it is best to do so after feeding
time and preferably under low-light or dark conditions.
Paradise Fish
Males of this species can be aggressive, but tend to temper their
aggression once a hierarchy has been established within the aquarium
population. Females will not display aggressiveness.
As was stated at the beginning all fish can be aggressive and all can
be passive. It is just a matter of you, the aquarium keeper, being
aware of each specific fish species’ temperament before blindly adding a
new member to your tank.
Always keep in mind that your fish selection should not be based
entirely on how beautiful a fish looks. Never abandon the temperament
and aggressiveness comparability factor. As long as you do this, even
the so called aggressive freshwater fish can be beautiful additions to
your aquarium.
Bad quality of water and high organic chemical level where many parachite and virus live will risk betta with many disease. It could be caused by food remnant especially if feeding them with pellet and marked by bad smell of water.The source of parachite and virus also could come from unclean food, so ensure the worm or mosquito larva are clean before feeding them with these foods.
Dropsy disease could be recovered by taking betta splenden out the contaminated water and put in clean water with some drops of antibacterial. If this method shows no progress then change the method by add the food with Oxytetracycline atau Chloramphenicol dosage of 0.05 mg/g of betta splenden weight for about 8 to 10 days. 
