No one likes to finger a particular fish. What is easy to keep in one person's tank may wreak havoc in the life of another person's. If you are just starting out, the fish listed below may not be good first choices for many reasons.
Iridescent Sharks, Pangasius hypophthalmus
They look great in the tank at the lfs. Small, shiny, great swimmers. They don't stay that way. They can grow to almost 3 feet. They are excitable and can smash against the aquarium wall at high speeds and injure themselves. During water changes they can exit your tank like a rocket. They also become nocturnal.
Bala Sharks, Balantiocheilus melanopterus
Another teeny tiny fish that grows HUGE.
Plecos, Hypostomus sp.
Everyone needs an algae eater, right? Plecos can again outgrow most tanks.
Chinese Algae Eaters
These are the Dr. Jekyll/Mr. Hyde's of fishkeeping. These little fellows start out small and eating algae. They grow large and then develop an appetite for your tank inhabitants. Algae eating fish are frequently mislabelled at your lfs. Be careful.
Knifefishes
Grow huge and if your favorite fish becomes smaller in size than their mouth, they get pursued quietly from behind and then sucked in.
Goldfish
Very familiar to many of us at fairs and as kids. Goldfish tend to be 'dirty', ie, carry parasites and nasty bacteria. They also don't belong in tropical tanks as they are coldwater fish.
Piranhas
Grow huge. Need space. Should be in schools. Feed them well or they get hungry. Many end up getting ill from being fed 'feeder' fish for owners who keep them to watch their eating habits.
Painted Glassfish, Pseudambassis ranga or Chanda ranga
Now, how did nature get these guys do have a fluorescent stripe on their back? Well, nature didn't. They were cruelly injected with dye. These poor fish have a higher likelihood of getting sick. If you feel sorry for them, complain to the lfs who bought them. If you decide to give them a home, they will benefit from some aquarium salt in the tank.
Many othered dyed fish
If you think that many fish come in sorts of fruit colors, think again. Strawberried, raspberried, blueberries. NOT!!! Injected. Victims frequently include white skirt tetras, some botias. Ask first before buying.
Elephant nose, Gnathonemus petersii
High maintenance for beginners. Nocturnal and usually needs to be fed at night. Needs a larger tank, meaty foods, can be aggressive.
Red-tailed catfish, Phractocephalus hemioliopterus
Grows HUGE. Do you have an 8 foot tank?
Various other cats
Catfish eat fish.....aquarium fish. They grow large even tho' they are small at the lfs. One common species is the Pictus cat. Others are the channel cat and the shovelnose cat.
Baby Whale, Petrocephalus bovei
Similar to the elephant nose. May prefer live foods.
Various Eels of the Spiny Nature, Mastacembelus
Tire track eels, Zig Zag Yellowtail Eel, Fire Eel, eg. All nocturnal predators, grow large and require large tanks.
Fishes of a delicate nature
Listed below are a few fish that are very easy to obtain at the lfs but, for many reasons, just aren't that easy to keep. Although not in the category of growing large or being aggressive, they CAN be problematic for some and might be better choices after you have some experience under your belt. A few to give thought about before purchasing include:
Brackish fish have different requirements than regular FW fish in that they need salt in their environment. Brackish areas are those near the sea or where freshwater approaches the ocean. Setting up these tanks requires some research and preparation and, perhaps, is best left for when you have a few more miles underneath your belt. Some brackish fish include:
The final choice of what goes in your tank is YOURS. This thread was meant as a springboard for you to do more research before taking one of these fish home. Use caution when relying on 'future plans for a larger tank' because one never knows what will happen in several months to years. Many lfs' will not take back a large fish, nor will public aquariums. Be a conscientious aquarist and stock your tank with fish that will grow into it comfortably.
Iridescent Sharks, Pangasius hypophthalmus
They look great in the tank at the lfs. Small, shiny, great swimmers. They don't stay that way. They can grow to almost 3 feet. They are excitable and can smash against the aquarium wall at high speeds and injure themselves. During water changes they can exit your tank like a rocket. They also become nocturnal.
Bala Sharks, Balantiocheilus melanopterus
Another teeny tiny fish that grows HUGE.
Plecos, Hypostomus sp.
Everyone needs an algae eater, right? Plecos can again outgrow most tanks.
Chinese Algae Eaters
These are the Dr. Jekyll/Mr. Hyde's of fishkeeping. These little fellows start out small and eating algae. They grow large and then develop an appetite for your tank inhabitants. Algae eating fish are frequently mislabelled at your lfs. Be careful.
Knifefishes
Grow huge and if your favorite fish becomes smaller in size than their mouth, they get pursued quietly from behind and then sucked in.
Goldfish
Very familiar to many of us at fairs and as kids. Goldfish tend to be 'dirty', ie, carry parasites and nasty bacteria. They also don't belong in tropical tanks as they are coldwater fish.
Piranhas
Grow huge. Need space. Should be in schools. Feed them well or they get hungry. Many end up getting ill from being fed 'feeder' fish for owners who keep them to watch their eating habits.
Painted Glassfish, Pseudambassis ranga or Chanda ranga
Now, how did nature get these guys do have a fluorescent stripe on their back? Well, nature didn't. They were cruelly injected with dye. These poor fish have a higher likelihood of getting sick. If you feel sorry for them, complain to the lfs who bought them. If you decide to give them a home, they will benefit from some aquarium salt in the tank.
Many othered dyed fish
If you think that many fish come in sorts of fruit colors, think again. Strawberried, raspberried, blueberries. NOT!!! Injected. Victims frequently include white skirt tetras, some botias. Ask first before buying.
Elephant nose, Gnathonemus petersii
High maintenance for beginners. Nocturnal and usually needs to be fed at night. Needs a larger tank, meaty foods, can be aggressive.
Red-tailed catfish, Phractocephalus hemioliopterus
Grows HUGE. Do you have an 8 foot tank?
Various other cats
Catfish eat fish.....aquarium fish. They grow large even tho' they are small at the lfs. One common species is the Pictus cat. Others are the channel cat and the shovelnose cat.
Baby Whale, Petrocephalus bovei
Similar to the elephant nose. May prefer live foods.
Various Eels of the Spiny Nature, Mastacembelus
Tire track eels, Zig Zag Yellowtail Eel, Fire Eel, eg. All nocturnal predators, grow large and require large tanks.
Fishes of a delicate nature
Listed below are a few fish that are very easy to obtain at the lfs but, for many reasons, just aren't that easy to keep. Although not in the category of growing large or being aggressive, they CAN be problematic for some and might be better choices after you have some experience under your belt. A few to give thought about before purchasing include:
- hatchetfish-can be prone to ich; they can and DO jump out of the tank when startled. Need to be in groups to reduce stress.
- glass cats-need to be in groups; like to have some current; can die for no apparent reason
- otos (otocinclus)-have been known to die soon after acclimation without any evidence of disease; theories include loss of the ability to digest food during transport
- pencilfish-sensitive to water conditions
Brackish fish have different requirements than regular FW fish in that they need salt in their environment. Brackish areas are those near the sea or where freshwater approaches the ocean. Setting up these tanks requires some research and preparation and, perhaps, is best left for when you have a few more miles underneath your belt. Some brackish fish include:
- scats
- monos
- various puffers
- archers
- Mollies; Poecilia sphenops, Poecilia latipinna, and Poecilia velifera (Though often a mix of two or more)
Mollies are often regarded as a Beginner Fish, seeing as they are Livebearers, which are considered some of the easiest fish to breed and keep. Mollies are pretty easy, as fish go, however they aren't as easy as say...your common Platy. Mollies need to be kept in either some salt, or if kept in freshwater, hard and alkaline water. If you have soft, acidic water you can still keep Mollies, however you will want to add salt. Without salt or hard, alkaline water, they are much more prone to disease, especially "shimmies". Some Mollies are raised in total freshwater, and can live in softer, acidic water, however it's not going to be healthiest or best for them.
Also, most Mollies get fairly large, and with Sailfins especially, the males can be aggressive. They need a larger tank then most Livebearers, so these aren't the fish to keep in your 10 gallon. Except possibly Balloons but even they should be kept in a bigger tank. Mollies are very hardy fish when kept in the right conditions, and I would recommend them to a Beginner as long as they have those conditions and a proper sized tank.
The final choice of what goes in your tank is YOURS. This thread was meant as a springboard for you to do more research before taking one of these fish home. Use caution when relying on 'future plans for a larger tank' because one never knows what will happen in several months to years. Many lfs' will not take back a large fish, nor will public aquariums. Be a conscientious aquarist and stock your tank with fish that will grow into it comfortably.
Flushing any fish live or dead is a very bad thing to even consider 
