Articles Stocking aquarium

The 8 worst beginner fish

January 1, 2013
kissing gourami

A lot of the most popular fish available in pet- and aquarium stores are surprisingly bad choices for beginners, and some of the least noticed species are actually very easy to care for. This can get very confusing, especially with most stores not being too helpful.

This is why I compiled a list of some the best and worst beginner fish for all the aquarists out there who are confused by all the contradicting info out there. If you’re a beginner trying to stock your aquarium responsibly, you may be surprised to hear which popular fish you’re better off avoiding!

If you’re a beginner, be sure to have a look at the list of best beginner fish as well!

Helostoma temminckii – Kissing gourami, Kissing fish

These gourami (pictured above) are popular aquarium fish due to their funny ‘kissing’ behavior. They are a very easy impulse buy and I imagine many are sold every Valentine’s day! What most starstruck lovers don’t realize, though, is that those adorable little fish with their kissy mouths can actually grow to up to 11 inch (25cm). Maybe not such a good idea for that 10 gallon after all, but unfortunately most people don’t realize this until their kissy fish has already passed away.

The adorable kissing behavior seen in these gourami is actually how they fight, not a display of affection; they meet mouths and push each other around the tank to determine which one is stronger. Unfortunately, kissing gourami will also try to defend their territory from other fish species and can literally bully their tankmates to death by attacking and chasing them all day long. Aquarium plants won’t be treated any better, because kissing gourami are omnivorous and love to nibble at any plants they can find. Kissing gourami are best kept in a large tank: at least 85 gallons (300L) would be a good idea. If you want to keep them with other fish, don’t go for calm, small or defenseless species.

Pterophyllum scalare, Pterophyllum altum, etc. – freshwater angelfish

Due to their complex social structures, angelfish need to live in groups in big tanks! Photo by Dennis Slangen.

Due to their complex social structures, angelfish need to live in groups in big tanks!
Photo by Dennis Slangen.

Angelfish can be a gorgeous centerpiece in a tropical aquarium. Few things are more beautiful than a group of these elegant fish swimming alongside each other, foraging and showing their natural behaviour.

Sadly, I often see angelfish being kept in conditions that prevent them from growing to their true potential and that can even cause them to get growth deformities. Most importantly, don’t keep just one of these fish. Try to get at least six of them so they can form breeding pairs and feel safe together – for 6 angelfish, an aquarium of at least 80 gallons (300l) is a good place to start. Because of the height they can reach, angelfish are best kept in an aquarium that’s at least 20 inch (50cm) high. This will prevent deformities and gives them space to swim and grow. If you really want to imitate their natural habitat, go for a South American biotope with dark water and plenty of Amazon sword plants.

Astronotus ocellatus – Oscar cichlid, Velvet cichlid

Though not considered extremely difficult to care for, these fish just don’t seem to get what they deserve. Some sites list 30 gallons (115L) as a minimum, but many uninformed fishkeepers choose to house them in even smaller setups. Not a great idea at all, as Oscars can reach a size of 13-14 inch (35cm).

I’d recommend about 120 gallons (450L) for one pair, and don’t go easy on the filtration. Don’t house them with smaller fish, because they might just consider those a quick easy meal. Oscar cichlids can be kept by beginners, but starting out with a smaller tank around 30 gallons with smaller fish to gain some experience first may be a better idea.

Photo by Jón Helgi Jónsson.

Carassius auratus – common and fancy goldfish

Everyone had one as a kid: a 40 cent feeder goldfish in a bowl. Mine was named Leon and I loved him, until I realized that the Leon I’d had for three years was actually 20 Leons that my parents kept replacing after they died.
Goldfish are one of the most popular aquarium fish species, but they are pretty hard to properly care for. Neither common goldfish nor fancies can live in a bowl. Commons are mainly pond fish, and fancies need at least around 20 gallons (75L) per fish to thrive. They can’t be kept alone, so you’re looking at a minimum of 40 gallons (150L). Why? Because they can grow up to the size of your underarm or foot. And goldfish produce a lot of waste, so a big aquarium isn’t enough; you’re also going to need heavy filtration. external canister filters meant for tanks double the size of your goldfish tank are preferable.

Even though they’re great pets with lovely personalities, goldfish don’t make good beginner pets. Don’t try to win one at the fair if you don’t have the pond or tank for it!

For more information on just why bowls and small tanks aren’t suitable for goldfish,have a look at this article.
For more information about goldfish keeping, have a look at the common goldfish caresheet and fancy goldfish caresheet.


Goldfish can grow very large.

Chromobotia macracanthus – Clown loach

Even though a lot of websites try to warn beginning aquarists about these fish, they’re still sold on a huge scale. When given the right care and enough space, clown loaches will show very interesting behaviour, but unfortunately most of them will never get this lucky. Because they’re usually sold when they’re still very small, it’s kind of hard to imagine that these cute little striped creatures can grow to up to 12 inch (30cm!).

Because of their need to live in groups of at least five, they will need an aquarium of at least 75 gallons (285l) with lots of filtration. Keeping the water extremely clean is a must for these guys, as they are very sensitive.

clown loach

Photo by Dennis Slangen

Balantiocheilos melanopterus – Bala shark, Shark minnow

Another one of those cuties that is sold in your average pet store around the corner, where they accidentally ‘forget’ to tell you they can grow to a size of 12 inch (30cm). They should also be kept in groups, will try to jump out of their tank when they get the chance and are actually endangered in the wild. Definitely not a great fish to start out with as a beginner. However, like clown loaches, this species is very interesting to keep.

If you have a 100+ gallon (400+L) aquarium with a width of at least 79 inch (200cm) lying around and are a more experienced fishkeeper, they are actually a great challenge. Be sure to try to find captive bred Bala sharks though, and remember to think before you buy.

Bala sharks are usually sold when they are still young and cute, but outgrow most tanks very quickly. Photo by Lerdsuwa

Carinotetraodon & tetraodon varieties – Puffer fish, puffers

Their intelligence, interesting behaviour and odd looks make puffer fish great pets that can be just as much fun as a cat or dog. There’s one problem though: these fish need very specific care. Their aggressiveness, need for bigger tanks, sensitivity and their specific diets make it very difficult to set up an aquarium for them.

There are many different kinds of freshwater and brackish puffers, but they are all very messy eaters and most species won’t tolerate any tank mates whatsoever, something that has caused many a fish to be brutally slaughtered. Many of people introduce puffer fish into their community aquarium to deal with a snail problem, but after all the snails are eaten, problems start to arise. Before you decide to get any kind of puffer, do your research! A great place to start is the full dwarf puffer caresheet.

carinotetraodon travancoricus

Hypostomus plecostomus, Glyptoperichthys gibbiceps etc. – Large Pleco varieties

When it comes to people buying fish and being absolutely shocked when doing research afterwards, these guys probably take the prize. Often sold as ‘great algae eaters that will do fine in small tanks’, Pleco varieties like the Sailfin Pleco and Common Pleco can actually grow to an adult size of about 20 inches (50cm), which means they require an aquarium of at least 150 gallons (~570L).

Obviously not a very good choice for smaller setups after all, and to make matters worse, most varieties aren’t even effective at removing algae nor are they suitable for a planted tank – plants will be dug up and sometimes eaten.
Although very hardy and fairly peaceful, I would definitely not recommend these fish for beginners because of the reasons listed above. Ancistrus varieties (Bristlenose Plecos) make a much better choice for beginning aquarists when it comes to Plecos, as they only grow to about 6 inch (15cm); one Bristlenose can comfortably live in a 40 gallon (150L) aquarium.

Common Plecos are often sold to beginning aquarists as algae eaters that grow to the size of the aquarium. Photo by Karelj

“Honorable” mentions

Some fish that would normally make fine beginner fish, have been badly bred for so long that inbreeding has made them weak and vulnerable to diseases. Examples of this are Dwarf Gouramis (Trichogaster lalius – formerly Colisa lalia) and Guppies (Poecilia reticulata). Both used to be very hardy and fairly easy to care for, but are now so vulnerable to disease (a study has shown that 22% of all Dwarf Gouramis from Singaporean fish farms carry the Dwarf Gourami iridovirus) that it’s very hard to keep them healthy or even alive.

If you want to keep Dwarf Gouramis or Guppies, I definitely recommend getting them from a reputable breeder. This way you have a better chance of finding healthy fish that won’t die within weeks.

Dwarf Gourami are actually very hardy fish, but inbreeding has caused them to become weak.

Please remember that surviving is not thriving. If you’ve kept Oscars in a 30 gallon tank before and it went well, that’s great. It still doesn’t mean that 30 gallons is an ideal environment, though. Read before you buy! Keeping your fish healthy and stress-free is much more important than owning as many fish as possible. If the correct setup is too expensive or too much work, choose another species.

If you have any suggestions for species to add to the list or want to share your experiences with these fish, be sure to leave a comment below. Happy fishkeeping!

Cover photo by Daniel Ahlqvist.

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  • Reply Tardis52 July 8, 2016 at 5:34 am

    How is a common thought tank size for an Oscar 30 gallons? I’ve seen Oscars the size of my 20 gallon, LITTERALY! I agree with your 120 gallon minimum, even though I have seen a well thriving Oscar in a 75 in my LFS (the owner actually takes care of the fish he keeps, and his employees have to know about the kind of fish by personal experience to offer advice, which is kewl). They really do love all the space they can get.

    • Reply Mari July 8, 2016 at 12:51 pm

      I know right?! I don’t understand it either. I included that because I came across multiple sites that listed something around that size while fact-checking for this article. And great to hear your local pet store owner takes good care of his fish, at least that way you can buy fish without having to worry about supporting bad animal husbandry 🙂

  • Reply Eric B December 29, 2015 at 4:54 am

    Personally, I think neon tetras could be on this list. They are thought of as stater fish by many people and because they are so colorful they are usually added to aquariums. However they are sensitive to water chemistry, particularly ph, so many die unless in mature aquariums. Add that to the fact they should be in schools so they should have a bigger tank despite their small size.

    • Reply Mari January 2, 2016 at 3:42 pm

      Thanks for the input! I actually never had much trouble with them, although I agree that many people have no idea what size tank they need.

  • Reply Christian November 11, 2015 at 12:27 pm

    Hi Mari. I have 5 tropical fish (1x molly 1x guppy 3x platy) and one Dwarf Flame Gourami. Is it a bad idea to only keep one or should I have pairs? Also he seems to be a tad sluggish but I think it might just be because he’s still getting used t the new tank. Is correct or is this a problem? I only got him today and have very good water quality so I don’t really know if there is anything wrong. He seems a little anti-social sort of in one corner all the time. Is this normal of Dwarf Gouramis?

    • Reply Mari November 12, 2015 at 6:58 pm

      Hi! There are unfortunately a few things wrong with your stock. The livebearers are all group fish, so if you want to keep them I would get rid of the molly and the guppy and expand my group of platies. It’s not ideal to even keep livebearers with dwarf gouramis, though, as they are both shy and territorial – that might explain his behavior, although if you’ve only had him for a day it could also be stress. As for keeping gouramis in pairs, that seems to be what most people do and recommend!
      In conclusion, I would personally figure out whether you want to keep gouramis or livebearers and then adjust your stock based on that, as the current situation is not ideal. I’m not sure what kind of tank you have, but be sure to keep in mind these species all need at least 15 gallons!
      Good luck 🙂 feel free to ask if you need any more help.

  • Reply Daniel Bortolini December 30, 2014 at 9:00 pm

    What about elephant fish and the feeder 15 cent goldfish that gets to be a foot long and all of your other fish that can fit in its mouth disappear?

    • Reply Mari January 7, 2015 at 3:50 pm

      Agreed! Goldfish are already mentioned, but elephant fish are indeed a pretty bad beginner fish as well. They are super sensitive, need really big tanks and are difficult to combine with other fish. Definitely not ideal for beginners!

  • Reply Lisa September 11, 2014 at 6:59 am

    And don’t forget the Red-tailed shark. The peaceful, playful schooling fish- Until it grows up.

  • Reply brian c August 11, 2014 at 3:31 am

    very true but what about…let me think for a sec…aha! discus, tiger barbs, and dyed fish.i think you should do these fish.

    • Reply Mari August 11, 2014 at 12:58 pm

      You’re right! Especially discus, I’ve seen some disastrous discus setups.

  • Reply Freya Moran January 27, 2014 at 2:57 am

    What is a good beginner fish then?

    • Reply Mari January 27, 2014 at 5:12 pm

      You can find a list with better beginner fish here! 🙂

  • Reply Signe December 31, 2013 at 10:29 am

    Thank You for the very advisable information! Many, if not all beginners make this mistake and choose species not suitable for beginners due to its size or behavior. Unfortunately pet shops personal very often gives totally wrong suggestion concerning good beginners fish.

    • Reply Mari December 31, 2013 at 11:03 am

      I agree! It’s a pity pet stores don’t try harder to give good info.

  • Reply Christine April 5, 2013 at 1:43 am

    Another fish that’s really popular (in the US at least) is bettas. People have this idea that they can live in bowls, vodka bottles and other similar containers. A lot of this is due to lack of education from pet stores and people trying to be ‘hip’ and keep them as decorations. 🙁

    • Reply Mari April 5, 2013 at 5:37 pm

      I know, the betta thing is absolutely ridiculous, I see it all the time and it really upsets me sometimes 🙁 I didn’t put them in this list because they’re actually not bad beginner fish at all, they’re relatively easy to care for but people STILL refuse to give them what they need.

  • Reply Jotynn March 16, 2013 at 6:11 pm

    I’ve kept Dwarf gourami before, and sure enough they kept in a pack and bullied most tankmates to death rather quickly, like their cousins, the kissing gourami. Luckily myself and my dad noticed the pattern and stopped getting small tankmates

    • Reply Mari March 16, 2013 at 8:10 pm

      That’s a pity 🙁 I think it’s because they prefer calm tankmates, so they get nippy and territorial towards the ones that are less calm.

  • Reply Izzy the Fish Girl January 3, 2013 at 6:40 pm

    One more fish that is a good honorable mention is the dwarf gourami. I don’t know if you have the same trouble in Europe, but in the US there is a large problem with the dwarf gourami iridovirus. Many sellers in the US get their fish from farms in Asia and a staggering 40% of dwarf gourami that come from these farms are carrying the virus. There is no cure for it, and the fish just wastes away. 🙁

    • Reply Mari January 3, 2013 at 6:55 pm

      I did hear from a lot of people that dwarf gouramis are weak due to inbreeding and viruses, they’d be fine as a beginner fish if it weren’t for that. :(Guppies have the same problem, I think I’ll include those two in the article. Thank you for the tip 🙂

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