Pachypanchax arnoulti

Pachypanchax arnoulti – Loiselle, 2006

Arnoult’s Killifish / Zono

Type specimens are F2 descendants of fish collected from a Pandanus-Dracaena swamp draining into a tributary stream of the Ikopa River flowing parallel to RN-4 at Antanimbary Village (17° 10’ 79” S, 46° 50’ 97”E).

PACHY-pan-chax are-NOOLE-tea

Named after the Jacques Arnoult in recognition of his many contributions to Malagasy ichthyology and who first introduced this fish, and other fishes from Madagascar, to science and to the aquarium hobby in the 1950’s

3.14 inches (8.0 cm) captive collections

Pachypanchax arnoulti has the longest head (30.2% ± 1.8% of Standard Length) of any Malagasy Pachypanchax species.  The absence of reduced pectoral squamation differentiates this species from P. sakaramyi and P. sparksorum.  Lack of red colouration in the body and fins, along with its enormous head, distinguishes P. arnoulti from both P. patriciae and P. varatraza.  The combination of more rounded dorsal and anal fins, a longer caudal peduncle, presence of a narrow iridescent white margin along both the anal and lower edge of the caudal fins in males, as well as the absence of discrete metallic lateral spots separates this species from P. omalonotus.

No known population differences observed.  In older specimens the topotypical population can develop amelanic patches on the dorsum which typically appear as irregular areas of coppery or brassy pigmentation. This colouration is more common in captive populations,

A review of the Malagasy Pachypanchax (Teleostei: Cyprinodontiformes, Aplocheilidae), with descriptions of four new species.
In: Zootaxa 1366: 1 – 44 (2006)

 This species has commonly been confused with Pachypanchax omalonotus and most of the literature published since 1950 dealing with various aspects of P. omalonotus biology actually deal with P. arnoulti. (Loiselle, 2006)

Boinakely River:

Namahota River:

Namahota River:

– 1928 by G. Petit.

Also known from:

– Basins of the Mahavavy du Sud and the Betsiboka River.

– Small estuaries that flow into the Mozambique Channel between these two rivers.

– Lake Kinkony and its satellite lakes

– Kamoro drainage

– Tampoketsa highlands

Conservation Status varies over the extensive range of Pachypanchax arnoulti. Within the Betsiboka-Ikopa drainage its numbers have declined significantly over the past half century. Recent efforts to collect specimens from streams near the town of Maevatanana, where Arnoult (1955) found it to be abundant, were unsuccessful. (Loiselle, 2006)

P. arnoulti has also become rare in the Ampijoroa Forest Reserve where it was once found in large numbers. (J.S. Sparks)

This species also appears to be under heavy pressure in it's type locale, and in the lower reaches of the Kamoro River. (P. de Rham)

Population numbers still appear strong in the upper reaches of the Kamoro River and in small streams between the mouth of the Betsiboka and Mahavavy du Sud. (P. de Rham)

N. Raminosoa (2002) reports populations are still strong in the Lake Kinkony satellite lakes.

Loiselle classifies Pachypanchax varatraza as a species of special concern based on WCU criteria (Loiselle, 2006).  This status recommends constant monitoring of populations for conservation purposes.

Pachypanchax arnoulti has been collected from a wide range of habitats. The Pandanus-Dracaena swamp from which type material was collected contained clear, tannin stained waters of low pH and very low general hardness. No aquatic macrophytes were observed at this location.

pH: 6.2 - 7.0

Conductivity: 16 - 34 µS

General Hardness: < 17.1 - 64.4 ppm

Xiphophorus hellerii

Paretroplus kieneri

Paretroplus tsimoly

Oreochromis mossambicus

Glossogobius giuris

Awaous macrorhynchus

North American populations stem from collections by P.V. Loiselle, R. Haeffner and J. Davidson in 1997 from Boinakely River and from the type locality.  Breeding populations existed at the New York Aquarium and at the Denver Zoo; most captive specimens originated from one of these institutions. 

Males compete for access to females and fatalities to both sexes do occur due to aggression.  Pachypanchax arnoulti can be very aggressive in tight quarters and dominant males will often kill females regardless of their readiness to breed.

Spawning in trios or 2:5 ratios can be accomplished in 10 gallon tanks but often results in the eventual death of subdominant males and all females. Increased success has been had in larger enclosures and the author recommends spawning populations of 10 individuals in 30 - 40 gallon aquariums be the norm.

In the wild:

In captivity:

Specimens do not appear overly prone to water chemistry or water quality issues

pH: 6.5-7.5

Temperature: 70-75 °F

dKH and dGH: 0-4°

Undergravel filter with frequent water changes of 20-30% is sufficient for breeding

The author spawns Pachypanchax sp. in trios or 2:5 ratios of males to females (but see note above).

Yarn mops may be supplied, but successful reproduction has taken place with only gravel substrate available.

Eggs can be allowed to hatch in the adult tank; some fry cannibalism by parents is normal, but with a constantly spawning group this behavior appears to wane with time allowing for the rearing of fry in the adult tank.