What about the Goldfish. They are cold water, and the frog is tropical.
Actually, goldfish are subtropical fish, most tropical temperatures provide no problems for them at all - it's all the extra waste they produce when their metabolism is sped up that's really the problem.
Before I you respond to me, keep in mind most of these are my opinions based off of facts.
No problem, I had assumed that, but to me it appears that you have misinterpreted some facts - especially in the relation to goldfish

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These specific fish don't really think as dogs do, and the dogs intelligence is much greater than any fish. If you trap a dog in a room, it will start whimpering and realize that it is... trapped... If you do this to a fish, it would take a much smaller area for it to realize it is trapped.
Not really a great comparison, even though (if I follow correctly) you are still limiting this conjecture to domestic
Betta splendens - I don't think you've considered habituation here.
These fish have lived their whole lives in tiny volumes of water, and as a result show no reaction to it.
As I'm sure even people in the betta section would testify, if you were to put a betta that had lived in a big volume of water all (or in some cases most) of it's life into a much smaller one - there would be a clear change in behaviour that you could compare to a dog whimpering.
Likewise, if a dog is habituated to a tiny area, it wont whimper or show any related reactions. You see this on these animal rescue shows on TV where they go into places like illegal dog breeders who keep the dogs in
tiny pens.
I wouldn't consider keeping the dogs in these conditions acceptable just because the animals are showing no reaction to it, and I'm sure you wouldn't either. So why is it considered acceptable with bettas? I'd say simply because few people really think about it enough, and some that do just don't value the fish enough to get a bigger tank (the "it's just a fish" people in petstores).
Fish do not really think as we do or as dogs do, because they just react upon their instinct to live.
I always find such statements interesting. It's a pretty big presumption and generalisation to make, without a background in neuroethology or a similarly specific field.
My view is basically that there is no way whatsoever for us to actually know things like that.
I do not advise putting fish into small tanks, but I really think that his tank setup is fine for the goldfish. These goldfish don't get as large as others. Maybe the filtration should be upgraded though...
With the outgrowing of the tank part, What is the problem to grow out a fish in a smaller tank? Many people do this with new younger fish. The younger fish must reach a certain size before they can be safe from larger fish in the aquarium. This isn't the case here, but he is still doing basically the same thing: growing out a fish in a smaller tank. When the fish gets larger, it will be added to the main aquarium. And yes, I do consider the life of dogs higher than a goldfish. I do not want to start an argument though, so please remember these are just some opinions.
If 3 Bala sharks and 3 blood parrots were in that small tank, I'm sure there would be a greater response because that is not proper fish keeping. These goldfish however, I feel the tank is less worse with them instead. Now I'm assuming you were speaking of the small temporary tank holding the parrots and 3 balas. There are only a couple goldfish, so a fair analogy would be the same number of blood parrots as there are goldfish if you consider their lives of equal value. Also the bala sharks would not be able to live to their full potential in his final tank, where these goldfish can.
I can only presume that you either failed to read the link to the post I provided, or totally dismissed it as rubbish.
It's true that these goldfish do not grow as big as regular goldfish - but they still grow
much too large for this tank. Fancy goldfish easily attain the size of 6" diameter swimming spheres (excluding fins), so I take it you've not seen fancy goldfish that have been grown in proper conditions.
The problem is (which you should understand if you had read the link) basically that goldfish get 'stunted' in small tanks due to a build up of metabolites. This is why goldfish always get much larger and live much longer when kept in ponds and huge tanks. Stunting creates big problems for the goldfish, the liver is usually the first thing to go and their immune system leaves them open to attach from any pathogen that makes its way into the tank. This is the fate of most goldfish.
Goldfish are just a type of carp that have been selectively bred for thousands of years.
Just because it's socially acceptable to have them living a completely inadequate environment does not make it right, and this is reflected by the views of people on goldfish forums and in the coldwater section here.
Carp are messy, large and active fish that have a stunting mechanism. You cannot keep 3 goldfish in a 2.5gal until they outgrow it, and even the mentioned 28gal would be too small for the whole life of the fish, as it would not allow them to 'live to their full potential'.
The only problem is that sometimes people let the feelings from frustration come out in their responses.
I'd agree with that, and I think that's due to the fact that text on the internet is a very limited medium for expressing emotions.
IMO people should just use more smilies in such situations

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I do think that a 2 gallon would be better for the betta, but I think that keeping one in a .75 gal is not wrong. I'm sure that a betta could live just as healthily in both situations, with proper water changes and such. I'm not sure if I read this statement right, but did you compare my 2 gallons to .75 gallons to the same as 100 gallons to .75? In my opinion, .75 and 2 gallons are both equal to one bucket pretty much. I don't keep small aquariums like this. I also don't want to start a huge debate about this, but a year ago the general consensus on this forum was that 1 gallon was appropriate.
As you say, you don't keep small aquariums, but trust me in that that is a very significant amount of extra space for the fish to move in a standard 2gal than there is in this wall thing.
I'm going to reserve my opinions on adequate tank sizes for bettas, as like I said, I feel the topic is so opinionated no argument ever prevails.
I respect what you said, and you brought up very important points in a coherent manor. I hope other members respond as you have.
Why thank you, your making me blush

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I really appreciate how civilised this is going, no name calling or anything!

Thanks for the intelligent discussion.