Basics : Fish Selection
Compatibility is discussed in the Tankmates page here.
On this page, I briefly provide some pointers on selecting fish from a pet shop.
First, know your water parameters. If you have very soft acidic water or very hard alkaline water, then select fish which agree with your parameters, rather than trying to change your parameters to agree with the fish. If your water is neutral or not to an extreme, then most aquarium fish will do well, except for a few which need extreme conditions. Fish will prosper best when they are kept on the species appropriate side of their pH scale, but close stable conditions are far more beneficial than an ideal conditions achieved with chemicals. Know the water parameters of your pet shop.
Basically, you want a fish which is behaving completely typical for the species, from a tank which is filled with healthy fish, and of a shape & appearance which agrees with your expectations. I realize this is a very broad statement, but it comes as a result of the wide variety of fish available.
For all purchases, inspect the fish you do not want that are in the same tank. Is there many genetic defects? This indicates poor culling and is not normally a concern to the average hobbyist (if you will be breeding, it might suggest a weak genetic line though). Check their abdomens. If concave (turned inward), this is a sign of disease and/or recent introductions and/or poor diet. All trouble indicators. Are the colours vibrant and as expected. A bit of fading might be acceptable from stressful pet shop conditions. Are the fins open, the fish active, curious, interactive with you, relaxed or nervous (all depends on species as well). Check all fins (you might have to wait till the fish turns around, but it is frustrating to get home and find out that one of the pectorals is misshapen). Watch for cloudy eye, white spots, dusting of powder appearance, atypical rapid respiration (gill flukes, or poor water or previously stressed conditions).
Details...(alphabetically)
Quick picks African cichlids, Apistos & dwarf cichlids, Angelfish, Barbs, Bettas, Cichlids (other), Corys, Danios, Discus, Goldfish, Gouramis, Livebearers, Loaches, Piranha, Plecos and Tetras & Rasboras.
African cichlids
Any fin damage to base will probably not grow back. Concave abdomen can be Malawi
bloat (disease, avoid). Colour intensity can be a good indicator of the fish's
high status in the tank's pecking order, and generally a good sign of health and
vigour. Alpha-male may also be over-aggressive in your tank, so some caution is
indicated. Generally, African cichlids are very hardy fish, and diseases are infrequent.
Selection is more of a process of achieving the right recipe of utaka and mbuna
at the right sizes, and ensuring the vegetarians are not in an environment where
they will be fed too much high protein, and your tank is species appropriate with
swimming area and/or rockwork. Adding Africans to a mature tank of Africans is
difficult. Adding mature Africans to a tank of mature Africans can be described
as futile. Tank size matters.
Apistos & dwarf cichlids
Look for species appropriate behaviour (darting about the bottom, curious, active)
and coloration. These fish are somewhat fragile (due to their size), susceptible
to Ich and other parasites. Look for sharp colours on Kribs (alpha male & female
should be easy to spot, catch the female first as her colours fade faster). Colours
and behaviour on Rams, and other Apistos. Look for fin outline as well and with
Keyhole cichlids.
Angelfish
Look for proper fin outline, check pectorals (side fins) for genetic defects. Check for short or open gill plates (other common genetic defects). Angelfish are commonly breed locally so culling is usually poorly done. Look for good activity level, curiosity, and willingness to stand up to you.
Barbs
Very tricky to diagnose sick barbs, as they often give no outward indication of trouble until it is just before they die. Look for dead barbs. Ich is an obvious and easily recognizable problem. Head standing is a bad sign, unless they were recently fed. Tail standing is always a bad sign. Fish should be extremely active tormenting each other as is their nature.
Bettas
In a cup or small bowl, look for a bubble nest (good sign). Fish should acknowledge
your presence, ideally flaring fins & beard. Clean cup water may mean there are
not being fed, or were recently water changed, and dirty cup water may mean they
are not being water changed or they are being fed. It's hard to deduce anything
from the water conditions. Proximity of Betta cups to personnel will give you
some clue as to whether they might be being forgotten or serviced properly. In
a tank, is the Betta in an alpha position or hiding in a plant? Carefully inspect
fins, outline and uniformity of colours. Avoid fish with faded patches anywhere.
Cichlids (other)
Larger South & Central American, as juveniles, inspect for damage, pecking order,
coloration. On larger fish, check willingness to stare you down. Attacking your
finger, while a good sign of health, might indicate an overly aggressive fish.
Usual checks for colour, damage, uniformity of opacity or reflectivity across
sides. Over developed fins on a small body may be indicative of a runt (avoid
unless this is want you are looking for).
Corys
Check activity level, solitary or shoaling behaviour? Check barbels (should be long or there might be a bacteria in their gravel). Check belly (pink and full, or concave). My experience is that their barbels will grow back if that is the only problem with them.
Danios
Check activity level (frantic) and coloration (dull colours are a bad sign, as
is any dusty appearance). Look for pine-coning of scales, white around mouth.
Check carefully for any dead fish in the tank.
Discus
Check fin outline, body outline, eye size appropriate to body size, colour patterns
and colour intensity. Fish should be active, curious, make eye contact, hunt around
for food, follow your finger slowly traced across the tank. Ask to see them fed.
Avoid specimens which you do not see eating. Bad signs are darkening, white film
on slime coat, clamped fins. Avoid tank if this is seen on any specimens.
Goldfish
Look for pine-coning, buoyancy problems (many are genetically predispositioned to swim bladder problems), cloudy eye, floating near the surface, sitting at the bottom. You want an continuously active, colourful curious fish, with good fin shape, and whatever other appearance specifics to the line (bubble eyes, pom-poms, pearlscale, oranda, etc).
Gouramis
Susceptible to fin contagions (fungus and bacterial) and mouth fungus (columnaris). Fish should be in the upper half, or poking around plants, active, colourful etc. Clamped fins, inactivity, sitting at the bottom, darkening are bad signs. Some risk with any fish from that tank.
Livebearers
Susceptible to a variety of parasites and bacterial contagions, clamped fins are the first warning sign. Sitting at the bottom and white patches are also bad signs. Fish should be active and colourful. Carefully inspect all the tank occupants for a white patch (around the mouth or just behind the base of the dorsal fin). If any found, avoid the tank.
Loaches
Ask how long they have been there. Many loaches are wild caught, potentially bringing
a plethora of parasites to your community tank. Scaleless fish, they are very
susceptible to Ich, and easily die from it. Good candidates for quarantine procedures.
Besides clamped fins, the most telling observation is a concave belly, either
from new arrivals not eating or internal parasites. Healthy loaches would normally
have a slightly wide & protruding belly if there is enough to eat.
Piranha
Look for bite marks. Chunks missing from fins will grow back (if they don't reach
the base), but colours will take some time to fill in the new growth. Bite marks
from body will sometimes not grow back completely. Bite which intersect the fin
rays will permanently prevent those rays from growing back. Look for damage around
the mouth area. Piranhas are very aggressive eaters in a pack and very fast growing,
consequently a little damage is not unexpected, and smaller specimens will show
more damage. Piranhas fare badly when displayed in a very prominent tank (with
lots of foot traffic) and will bite each other when nervous. Best piranhas are
kept in a back room, so make inquiries. If none in stock, try to visit as soon
as new stock arrives (to improve your selection).
Plecos
Look at their colour. For medium coloured plecos (ie: common pleco), avoid any
which are very light coloured or very dark (stress signs). Check their belly for
evidence of appetite and consumption. Avoid if concave, unless you are planning
a rescue mission. Check their pattern carefully, as rarer plecos are often mixed
in with common plecos.
Tetras & Rasboras
Inspect the tank for cadavers. Coloration and level of activity are your best clues, and should be shoaling somewhat (varies). Look for white patches on body or mouth, Ich and for darkening or fibrous appearance on the sides (under the skin).
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