PFK Articles: Breeding Nannostomus mortenthaleri

[AquaticQuotient.com]

Dr Karel Zahradka explains how to keep and breed the stunning pencilfish, Nannostomus mortenthaleri. Here is an extract of the article.

Copyright © Practical Fishkeeping

Several years ago, the aquatic press reported on a fish called Nannostomus sp. "Peru" or "Peru Red", which was the name under which this species had been imported into Europe. Photographs caused great interest, and its arrival was eagerly awaited. Apparently, the fish was found in a remote area of the Peruvian forests, and transporting them to an export station in Lima was difficult.

This probably explained why the fish supplied to the Czechoslovakian market were in poor condition and difficult to acclimatise. They were thin, eating only brineshrimp nauplii, and they seemed to die for no apparent reason. This, combined with a high price, accounted for the first reported breeding, by Bork, being only as recent as 2001.

Originally, the fish was thought to be the red form of Nannostomus marginatus. Paepke and Arendt described it in 2001 as N. marginatus mortenthaleri in honour of a Mr. Mortenthaler, fish hunter and exporter.

However, it differs significantly from N. marginatus, compared to which it is bigger and more robust in general body shape. It shows less sexual dimorphism, apart from when in breeding condition, and is therefore very difficult to sex, except during the spawning period, whilst N. marginatus is relatively easy.

To add to the confusion, exporters started offering another fish under the name of Nannostomus "Peru Red", or N. marginatus "Red". Although the females of this other species are indistinguishable from N. marginatus, the males, although identical to N. marginatus in body shape, are coloured blood red from the middle of their body up to the caudal. I was even told by an importer that both varieties were offered under the name of "Peru Red" and, if ordered, either species might be supplied. However, it appeared not to matter, as there was a high demand for both species despite their high price!

Returning to N. mortenthaleri, they come from forest tributaries of middle and upstream reaches of the Rio Nanay in the northern part of Peru. The distance and difficult access to the locality explains the fishes’ poor condition when first imported.


Watch the males...
I acquired the first ten imported specimens in 2002. The fish were thin, timid, and died one after another, but showed no symptoms of illness. Only now have I discovered my mistake – that the tank in which I had been keeping them was too small. It was only when the last male remained that I realised that males are very aggressive towards each other and can kill each other if kept together within a restricted space. The last remaining male lived with me in solitude for another two years.

This might have been an end to my experiments with this fish had it not been for the fact that almost at the same time, a well-known aquarist living in the town of Pribram, Martin Mates, purchased two pairs. Not only had he kept them alive, but bred them on a limited scale. Thus, it is thanks to him that I was able to own this beautiful species again, and this time it was an F1 generation and, therefore, the further details relate to F1 fish.

The young fish I bought were healthy and accepted brineshrimp, cyclops, gnat larvae and clean, fine tubifex. As a treat, they get Daphnia, which they hunt greedily, and "suck out" the contents, letting the remains fall to the bottom. I have found it wise to put a few live Daphnia in the breeding tank for food, as it reduces the risk of the adults eating their own eggs after spawning. Varying their food is important because what the fish eagerly consume one day will be rejected the next and they could starve. The only exception to this is brineshrimp, which they will happily consume every day, but this does not correspond to the physiological needs of a freshwater fish. Ordinary mains water with a pH of around 7.0 is acceptable.

Intra-species aggressiveness of F1 generation fish is not so high as in wild caught specimens and usually stops short of actual killing.


Complete article by Dr Karel Zahradka here...

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[blackBRUSHalgae]

yes yes the males sure are aggressive among each other, which I witnessed at C328's small little 10cm cube tank that they use to store them.