Some fish aren't growing

[Naughts]

Do you de-worm the fish? If not I would try it, it results in healthier fish.
There is always the genetics factor, as mentioned above.

 

[Ichthys]

I would at least double the water changes. Fish produce pheromones that prevent each other from growing. Growth rates tend to be more related to this than food or tank size. The more water changed, the faster fish grow.

 

[Colin_T]

How often do you feed them?
How much do you feed them?
Their diet could do with a bit more variation.

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To grow fish quickly, you want warm water (28C), lots of big regular water changes and gravel cleaning, a clean filter, and a varied diet fed regularly. Miss out on any one of these and the fish won't grow as quickly as they could.

The other reasons fish don't grow is parasites like gill flukes and intestinal worms, and bullying from bigger or more dominant fish.

The fact some fish have grown but others haven't would suggest bullying, lack of food and parasites like intestinal worms. Naughts mentioned deworming the fish and that would be a good way to start.

Feed the fish 3-5 times a day and give them as much food as they can eat. Don't put it all in at the same time, just offer a bit and let them eat it, then offer a bit more. Continue doing this until they are full and stop racing in to eat the food. You should add raw/ cooked prawn/ shrimp, and other marine foods (fish, squid, etc) to their diet. You can buy frozen foods like brineshrimp, mysis shrimp, daphnia and marine mix (prawn, fish & squid blended up) from most pet shops and these can be fed each day in addition to the dry foods you use. You can add some plant matter, especially for the rainbowfish, whose diet should consist of 50% plant based foods.

Do big regular water changes every day or two when feeding more often so the tank remains clean. Maintain the filter too.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Deworm all your fish. See section 3 of the following link to deworm the fish for thread and tape worm.

What to do if your fish has Stringy White Poop.

Fish do a stringy white poop for several reasons. 1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be...

www.fishforums.net

If there's no improvement after that, then it is probably bullying or the fish are genetically stunted.

 

[Ichthys]

Prawns should not be fed to fish. They contain thiaminase, which breaks down vitamin B1 (thiamine) which will lead to all sorts of issues if fed too much, including poor growth.

 

[FishNewbie82912]

Wow thank you guys!

 

[Colin_T]

Prawns should not be fed to fish. They contain thiaminase, which breaks down vitamin B1 (thiamine) which will lead to all sorts of issues if fed too much, including poor growth.

Fish eat prawns every day and are fine. I fed prawn to most of my fish on a daily basis for years and never had a problem. The only reason to be wary when feeding prawn/ shrimp to aquarium fish, is if you have live shrimp in the tank. If you do have live shrimp, then you should use cooked prawn for the fish so no diseases get introduced to the shrimp in the tank.

 

[Ichthys]

Fish eat prawns every day and are fine. I fed prawn to most of my fish on a daily basis for years and never had a problem. The only reason to be wary when feeding prawn/ shrimp to aquarium fish, is if you have live shrimp in the tank. If you do have live shrimp, then you should use cooked prawn for the fish so no diseases get introduced to the shrimp in the tank.

If you’ve been using the little frozen ‘prawns’ we use for prawn cocktails and prawn sandwiches, they’re not prawns, but a species of shrimp. Shrimp are safe, prawns are not. Those little ‘prawns’ are pre-cooked, btw.

 

[Myraan]

Where did you get the idea that prawns contain thiaminase and shrimp do no not? For that matter I was of the understanding that shrimp and prawn are virtually synomonous, the different words referring to size, but different cultures use them differently. British (and commonwealth) english uses "shrimp" for small and "prawn" for large. American english uses "shrimp" as a more catchall.

https://www.practicalfishkeeping.co...ed-to-know-about-predator-fish-and-thiaminase says that thiaminase is found in cyprinid fish, mussels, and crustaceans

Both shrimp and prawns (which are common name classifications not scientific; both are decapods as are crabs, lobsters and crawfish) are crustaceans. In fact, a fish fed on nothing but brine shrimp and/or daphnia might also have problems.

Thiaminase will probably be destroyed by cooking, but it also probably destroyed all the thiamin in the food before cooking.

Regardless, shrimp and prawns should not be the main diet. I think the main issue about thiaminase is that feeder goldfish are a really bad choice of live food.

 

[Ichthys]

Where did you get the idea that prawns contain thiaminase and shrimp do no not? For that matter I was of the understanding that shrimp and prawn are virtually synomonous, the different words referring to size, but different cultures use them differently. British (and commonwealth) english uses "shrimp" for small and "prawn" for large. American english uses "shrimp" as a more catchall.

https://www.practicalfishkeeping.co...ed-to-know-about-predator-fish-and-thiaminase says that thiaminase is found in cyprinid fish, mussels, and crustaceans

Both shrimp and prawns (which are common name classifications not scientific; both are decapods as are crabs, lobsters and crawfish) are crustaceans. In fact, a fish fed on nothing but brine shrimp and/or daphnia might also have problems.

Thiaminase will probably be destroyed by cooking, but it also probably destroyed all the thiamin in the food before cooking.

Regardless, shrimp and prawns should not be the main diet. I think the main issue about thiaminase is that feeder goldfish are a really bad choice of live food.

It’s a very common misunderstanding.

It’s scientifically well documented that most species of prawn contain thiaminase and most species of shrimp do not.

The terms are used interchangeably all over the world but in fact they’re not even closely related. They’re both Decapods but they’re from different suborders.
This first result from a google search explains the differences...

Prawns vs Shrimp: What's the Difference?

Prawns and shrimp are closely related and often confused. This article explores the key differences between shrimp and prawns.

www.healthline.com

 

[Myraan]

Ok... but Tiger Shrimp is a type of prawn.... and commonly sold as food. King Prawn, another prawn, is also known as Whiteleg Shrimp, and the small prawns we buy are usually Pandalus borealis, a type of shrimp but have several common names half of which contain shrimp, the other half prawn.

I couldn't find the well documented evidence about the difference in thiaminase content between the two sub-orders, but you are probably right, I just couldn't find it. The prawn clade seems to quite basal to Decapoda, and if they mostly contain thiaminase, it is not unlikely that least some of the other decapods do too, unless the gene was lost early in the other clades.

Going by wikipedia though, naming the prawn sub-order as such has no actual citation, so I would still regard the term as non-scientific, but that's beside the point.

If you are right, the next problem is - are the shrimp and prawns we buy for labelled such that we know which sub-order they are from? (without googling the scientific name)

Haha - I think thiaminase content is irrelevent unless you feed the item raw daily or cooked exclusively, but you piqued my interest.

 

[Ichthys]

In short, prawns are straight and shrimps are curved. It’s to do with differences in the body segments. Each prawn body segment overlaps the next, front to back. In shrimp the second body segment overlaps the first and third, giving them their distinct curved shape.
Prawns are suborder Dendrobranchiata, Shrimps are suborder Pleocyamata.

 

[Myraan]

That doesn't change the fact that as far as buying food goes, Prawns are frequently sold as shrimp and Shrimp are almost always labelled prawns, so telling people prawns will poison their fish but shrimp are fine is not helpful, even if you regard thiaminase as a problem.

 

[Ichthys]

It’s certainly more helpful than not telling them. The information is out there if they choose to follow it up.

 

[gilpi]

I don't think your tank is over stocked but yes as mentioned, lots of water changes and a good variety of food is the best we can do.

 

[fishyfun&fans]

you need to make sure your fish get a varied diet i.e Cucumber in the morning flake at lunch and brine and spirulina blocks for tea mix it up a little try pellets wafers different human veggies but blanched

also check for white stringy poop and treat accordingly as white stringy poops are usually worms