Runty Tetras. Does this happen? - Tropical Fish Keeping - Aquarium fish care and resources
 
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post #1 of 8 Old 02-02-2011, 09:00 AM Thread Starter
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Runty Tetras. Does this happen?

So, as you can see from my signature, I have a largeish school of Pristella Tetras (Pristella maxillaris) in my 55g tank. I've had these guys for the better part of a year now and they have grown up quite a bit. Most are very deep bodied now and I'd say approaching two inches. Nice fish. Anyway, two fish in the school have yet to develop this deep body and are somewhat shorter. Say 1.5 inches. I've been worried on and off about these two but after paying attention they seem to eat at least some when fed and are otherwise accepted by the group and normal.

Are there just runty fish? Or is it possible these two have some sort of parasite? I can't help feeling that they're fine, even though they differ in size pretty remarkably. Thoughts?

30g SE Asian Tank
15 Lambchop Rasbora
2 Gold White Cloud Minnows
3 Dwarf Chain Loaches
2 Powder Blue Dwarf Gourami

55g Amazon Tank
2 Wild Type Angels
1 Marble Angel
1 Black Angel
1 Koi Angel
2 Bolivian Rams
14 Pristella Tetra
10 Dwarf Pencilfish
2-3 Twig Catfish (to come)
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post #2 of 8 Old 02-02-2011, 09:45 AM
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I have the same with my pristellas (and also my glowlight tetras). Some are large and some don't seem to grow as big, despite being in the tank for 6 months and feeding fine. I found the smaller individuals could be more aggressive too. I started a thread about this ages ago and Byron said he had the same experience. I can only conclude that the fish are genetically different from one another - and therefore are different physicaly (unless it's a parasite, which seems unlikely as I'd expect it to spread to all individuals). A possible explanation for the genetic difference is that the wild stock might have been collected from different locations... who knows
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post #3 of 8 Old 02-02-2011, 12:50 PM Thread Starter
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It makes enough sense I suppose. And you're right. I'd expect a parasite to spread to everyone.

30g SE Asian Tank
15 Lambchop Rasbora
2 Gold White Cloud Minnows
3 Dwarf Chain Loaches
2 Powder Blue Dwarf Gourami

55g Amazon Tank
2 Wild Type Angels
1 Marble Angel
1 Black Angel
1 Koi Angel
2 Bolivian Rams
14 Pristella Tetra
10 Dwarf Pencilfish
2-3 Twig Catfish (to come)
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post #4 of 8 Old 02-02-2011, 06:35 PM
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As sik80 mentioned, I do have this with Pristella, actually several other fish species too. Some seem to grow fast, some grow much slower, very little at all. As long as they are normal I don't worry. If they develop black blotches or white patches or something, that's very different. But healthy fish...not to worry.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #5 of 8 Old 02-03-2011, 06:22 PM
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I have not kept the Pristellas but could it be that the larger, deeper bodied ones are the females and the smaller, slimmer ones are the males?

150 Gallon - Mostly American Cichlids
135 Gallon - Angelfish Community
75 Gallon - Odd couple (Polleni/Angelfish)
55 Gallon - African tank
20 Gallon Long - QT
10 Gallon - Empty
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post #6 of 8 Old 02-03-2011, 06:33 PM
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Quote:
Originally Posted by jeaninel View Post
I have not kept the Pristellas but could it be that the larger, deeper bodied ones are the females and the smaller, slimmer ones are the males?
I had initially thought much the same jeaninel, but as I observed this over time there seem to be males and females among the 10 "larger" fish judging by their girth and behaviours. The two smaller fish are about half the size of the rest.

Byron.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #7 of 8 Old 02-03-2011, 07:36 PM Thread Starter
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I had also thought of this, but the mathematical odds that in my school of fourteen I come out with a ratio of 12:2 is pretty low.

Incidentally, what sort of behavioral differences are there between fish of different sexes in the Pristellas?

30g SE Asian Tank
15 Lambchop Rasbora
2 Gold White Cloud Minnows
3 Dwarf Chain Loaches
2 Powder Blue Dwarf Gourami

55g Amazon Tank
2 Wild Type Angels
1 Marble Angel
1 Black Angel
1 Koi Angel
2 Bolivian Rams
14 Pristella Tetra
10 Dwarf Pencilfish
2-3 Twig Catfish (to come)
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post #8 of 8 Old 02-03-2011, 07:57 PM
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Quote:
Originally Posted by burnsbabe View Post
I had also thought of this, but the mathematical odds that in my school of fourteen I come out with a ratio of 12:2 is pretty low.

Incidentally, what sort of behavioral differences are there between fish of different sexes in the Pristellas?
The males display, not a lot, but I find all characins do to some extent. Sort of sidling up side by side and turning a bit on one side, sometimes with a slight quiver. Then there is the male "nudging" of females, presumably trying to push her into a plant thicket.

I've observed rummynose doing the above, and my Pretty Tetra do too.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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