What Does the Skeleton of a Malawi Cichlid Look Like?

Alizarin skeletal preparation of Melanochromis auratus

ntire specimen of Melanochromis auratus, an endemic Lake Malawi haplochromine cichlid of the mbuna species flock, cleared and stained using the technique of Dingerkus & Uhler, 1977. Bones are stained purple using Alizarin Red S and cartilage is stained blue with Alcian Blue; muscles have been digested using trypsin enzyme, rendering the entire (skinned, eviscerated) specimen transparent once it is placed in glycerine. It is now straightforward to dissect and draw the skeletal units and compare them with those of other species to obtain comparative osteological data for use in deriving phylogenetic hypotheses and classifications.

Skull bones of
Heterochromis multidens, a basal African cichlid from the Congo basin Neurocranium (skull) of a phylogenetically basal African cichlid, Heterochromis multidens from the Congo River. Abbreviations: B, blind cavity, not connected with lateral-line system; BOC, basioccipital; BS, basisphenoid; CC, external aperture of carotid canal; EO, epioccipital (epiotic); EOC, exoccipital; EOF, epioccipital facet for articulation with dorsal arm of posttemporal; F, frontal; IC, intercalar; IX, foramen of glossopharyngeal nerve; LE, lateral ethmoid; N, nasal; NLF_1-5, lateral-line foramina; PA, parietal; PRO, prootic; PS, parasphenoid; PTO, pterotic; PTS, pterosphenoid; PV, vomer; SOC, supraoccipital; SPH, sphenotic; X, foramen of vagus nerve. Compare with next drawing. [From Oliver, 1984.]

Below: Neurocranium (skull) of a Lake Malawi endemic haplochromine cichlid of the "Hap" flock, Placidochromis milomo, in left lateral and dorsal views. [From Oliver, 1984.]

Skull of
Placidochromis milomo from Lake Malawi

Below: Bones of the jaws and suspensorium of the left side in Otopharynx lithobates (87.2 mm SL) of the Malawi "Hap" flock. Abbreviations: AA, anguloarticular; DN, dentary; ECT, ectopterygoid; END, endopterygoid; HM, hyomandibular; MPT, metapterygoid; MX, maxillary; PAL, palatine; PM, premaxillary; POP, preopercular; Q, quadrate; RA, retroarticular; SYM, symplectic. The upper jaw consists of the premaxillary and maxillary; the lower jaw consists of the dentary, anguloarticular, and retroarticular. [From Oliver, 1984.]

Jaw bones and
suspensorium of Otopharynx lithobates from Lake Malawi

Below: Lower pharyngeal bone (fused fifth ceratobranchials) of Exochochromis anagenys (200 mm SL holotype), a Lake Malawi endemic haplochromine cichlid of the "Hap" flock, in (a) occlusal (anterodorsal), (b) left lateral, and (c) posterior views. A cichlid feeds by first obtaining a food item, such as a small fish, with its jaws (shown in drawing above). The fish then passes the food back into the throat where there is, in effect, a second pair of jaws — the lower pharyngeal bone (seen in this drawing) in the floor of the throat, with teeth pointing upward, and the upper pharyngeal bones (see next drawing) in the roof of the throat, with teeth pointing downward. In cichlids, unlike most other fishes, it is this second pair of pharyngeal "jaws" that actually chew the food. [From Oliver, 1984.]

Lower pharyngeal bone of Exochochromis anagenys from Lake Malawi

Below: Upper gill arch elements of the right side in another Malawi haplochromine of the "Hap" flock, Nimbochromis venustus, 119 mm SL. Dorsal view shown in left half of drawing, ventral view of same elements in right half. Cartilage is stippled densely, bone lightly. Abbreviations: C-EB₂, cartilaginous extension of second epibranchial; EAC, epibranchial accessory cartilage; EB_1-4, epibranchials; GR, uppermost gill raker of first arch; PB_1-3, (infra)pharyngobranchials; TP_2-3-F, tooth plates fused with the associated pharyngobranchials; TP₄, fourth tooth plate (unfused). [From Oliver, 1984.]

Upper gill arches
of Nimbochromis venustus from Lake Malawi

Below: Caudal skeleton of Cyrtocara moorii, 35 mm SL, showing elements found, with some individual variation, throughout the Malawi haplochromines. Cartilage is stippled densely, bone lightly. Abbreviations: EP, epurals; H_1-5, hypurals; HPU_2-3, hemal spines of preural centra; NPU_2-3, neural spines of preural centra; PH, parhypural; PU_1-3, preural centra; U₁, ural centrum; UN, uroneural. [From Oliver, 1984.] Caudal skeleton of
Cyrtocara moorii from Lake Malawi

Caudal skeleton of
Cyrtocara moorii from Lake Malawi

The Cichlid Fishes of Lake Malawi, Africa: MalawiCichlids.com