Redtail catfish for cycle?

Are redtail catfish ideal for cycling a new tank? I am getting a 55liter tank and I was thinking of either a redtail or oscar...
Answers:
First of all, a lone Oscar needs a 55 Gallon tank, a 55 litre is not even close to being big enough for this fish that reaches 16" long. A red-tail catfish needs hundreds of gallons because they get so massive they would dwarf an Oscar (an adult would need about a 1200 gallon tank!) If it's red tailed shark you meant, they still get too big for your tank, growing to 8" and getting aggressive. It is very important for you to research what fish you get before getting them. 55 litres is a small tank, and you need to stick to small fish. Forget every idea you have right now and start over. In a 55 litre tank you don't want any fish that will grow over 4" long.
As far as catfish go, look at Corydoras - they're about the only type of catfish that won't outgrow your tank. You can use them to start your cycle because they are fairly low-waste fish, and as long as you only start with no more then 3, and don't add any more fish until the cycle is over, it will work.
But do yourself a favour and don't get fish until you've developed a basic stocking plan for your tank, ensuring what you have chosen are compatible, won't outgrow your tank, and that you know how to keep them properly.

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I really hope you are joking, Red tailed catfish are a fish that needs at minimum 500 GALLONS. Oscars need minimum 55g. SO NO you can't get neither without stunting their growth sadly leading to there death.

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I hope you are joking as well because both an Oscar and DEFNITELY a red tail catfish will need more than 55 liters! That's about 15 gallons!!
And please do not cycle with fish. It is completely unecessary.
Please research other fish and come back with a suitable stocking plan...