Tuesday,17 September 2019, 6 : 51 PM

Ptychochromis onilahy

P ONIHALY
Ptychochromis onilahy
Image Credit: Ian Heart

Introduction



Ptychochromis onilahy is a medium sized fish which has never been seen since its initial description in 1962.
It was initially found in Onilahy river in southwestern Madagascar and has not been sighted since.
However the Onilahy river system is large and there might be small isolated populations.


Taxonomy

(Click for details of Cichlid taxonomy)

Ptychochromis onilahy Ptychochromis onilahy was first described by Stiassny & Sparks , in 2006.
The genus Ptychochromis was described by Steindachner in 1880.
The species name Onilahy is derived from Onilahy river system, the only known sighting of this fish.



Description

Ptychochromis onilahy reaches a length of about 5.1 " (SL).
Body is deep and laterally compressed.
Lateral snout outline is straight.
Predorsal head profile is convex from middle of eye to dorsal-fin origin.
Dorsal body profile from dorsal-fin origin is smoothly convex.
Ventral(lower) body profile is more or less straight.
Caudal peduncle is short, deep, and laterally compressed.
Dorsal-fin origin is located anterior to vertical through pectoral-fin insertion.
Pelvic-fin origin is located well posterior to vertical through pectoral-fin insertion.
Total vertebral count is 26 or 27, with 13 vertrebra located on body and 13-14 located on caudal region.
Lower and upper jaws are similar (isognathous).
Teeth in jaws are bilaterally symmetrical and bicuspid, with crowns some what expanded distally and slightly recurved.
Outer row teeth of both jaws are enlarged and graded in size laterally.
Like all cichlids, P. onilahy have pharyngeal teeth.
Upper and lower pharyngeal tooth plates are well developed with strong teeth.
Body is covered with large, regularly imbricate, weakly ctenoid scales from about level of midorbit to proximal portion of caudal fin.
Scales above upper lateral line to about level of origin of soft dorsal fin are cycloid.
Scales on flanks becoming increasingly ctenoid posteriorly, but at most only weakly so.
Scales on nape and head regionare cycloid.
There are four or five rows of cycloid scales on cheek.
Scales on opercle and subopercle missing in all specimens.
Anterior chest scales are reduced in size and embedded.
Scales on chest are weakly ctenoid, except anteriorly where they are cycloid.
Scales on belly are cycloid.
Snout, and region near eyes does not have any scales.
Scales on caudal fin reduced in size.
Lateral line has 33 or 34 scales.
There are five scales in diagonal from lateral line to dorsal-fin origin.
There are four or five scale rows between bases of pectoral and pelvic fins.
No scale rows present along dorsal- and anal-fin bases.
Dorsal fin is placed vertically above pectoral fin base, slightly anterior and has XII spines, 12 soft rays.
Anal fin has III spines and eight or nine soft rays. First anal spine is very short, second and third spines elongate and of similar length.
All fins in preserved specimens were damaged, making determination of original fin shape impossible.
Pelvic fins are short, and extend to origin of anal fin.



Distribution & Habitat

Ptychochromis onilahy Ptychochromis onilahy was initially found in Onilahy river in southwestern Madagascar and has not been sighted since.
However the Onilahy river system is large and there might be small isolated populations.

Habitat :



Colouration



According to Kiener( 1963) and Kiener and Mauge´ (1966), adults of this species were uniformly gray brown, paler ventrally and lacking any obvious body markings.



Conservation Status & Threats



IUCN lists this as an undescribed species with voucher specimens held at MNHN.
It has not been collected for many years despite targeted efforts within its former range.
Five preserved specimens represent the only known material collected from the Onilahy River in 1962.
The main impacts thought to have caused the decline of this species are deforestation leading to loss of habitat through increased sedimentation, competition from introduced tilapias and overfishing.
This species is assessed as Extinct.

Major Threats:



Tank Size and setup:



Species Snapshot

Species Card


Particulars Details
Scientific Name Ptychochromis onilahy
Common Name
Genus Ptychochromis
Subfamily Ptychochrominae
Geographical Origin Africa: Madagascar.
Diet
Gender Differences
Breeding
Temperament
Con Specific Temperament
Water hardness
Difficulty Level in Aquariums


Morphometric Data


Particulars Details
Total Length(inches)
Standard Length(inches) 3.10

Measurements as % of Total Length


Particulars Details
Body Depth 45.50 %
Head length 33.90 %
Pre Dorsal length 33.60 %
Pre Pectoral length  %
Pre Anal length 74.20 %
Pre Pelvic length 40.40 %
Caudal Peduncle Depth 19.40 %
Caudal Peduncle Length 14.50 %
Fork length  %
Length of Last Dorsal Fin Spine  %
Pectoral Fin Length  %
Pelvic Fin Length  %

Measurements as % of Head Length


Particulars Details
Head Width  %
Snout length 34.30 %
Eye diameter 26.70 %
Pre Orbital Length  %
Inter Orbital Width  %
Pre Orbital Depth  %



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