Ageneiosus marmoratus EIGENMANN, 1912

Bottlenose Catfish

Etymology

Ageneiosus: from the Ancient Greek ἀ- (a-), meaning ‘without’, and γένια (génia), meaning ‘beard’, in reference to this species’ very small barbels.

marmoratus: from the Latin marmoratus, meaning ‘marbled’, in reference to the species’ colour pattern.

Classification

Order: Siluriformes Family: Auchenipteridae

Distribution

The holotype was collected from a creek below the settlement of Potaro Landing in the Potaro-Siparuni region of central Guyana which almost certainly refers to a tributary of the Potaro River, itself an affluent of the much larger Essequibo system.

Current knowledge suggests it to occur over a huge area since its also been recorded from the Courantyne/Corantijn basin in western Guyana and Suriname, the upper Amazon region in Peru and Ecuador, and there is also a questionable record from the Paraná drainage in Argentina.

Habitat

Given its enormous natural range this species is likely to be something of a habitat generalist, but most records we’ve seen pertain to the lower sections of river channels and larger tributaries.

Maximum Standard Length

Given as 185 mm by most sources though some hobbyist reports suggest it can grow larger.

Aquarium SizeTop ↑

Minimum base dimensions of 150 ∗ 60 cm cm are required for long-term care since this active species can sometimes behave skittishly and may injure itself by swimming into aquarium glass.

Maintenance

Ideally a soft, sandy substrate should be used though it is not essential. Additional furnishings are as much a case of personal taste as anything else but the most favoured set-ups tend to feature relatively dim lighting plus some chunks of driftwood and scattered tree roots/branches.

Some water-worn rocks can also be included if you wish, but be sure to leave plenty of room for swimming as this species tends to spend a significant amount of time in open water once settled.

Efficient filtration is a must when keeping predatory species due to the amount of waste produced so install one or more external canister filters and/or a sump system, organising the return in such a way that some surface movement and a degree of flow is created.

Weekly water changes of 30-50% should be considered mandatory as this species can be sensitive to organic pollutants, and therefore must never be introduced to biologically immature set-ups.

Water Conditions

Temperature: 22.5 – 26 °C

pH: 6.0 – 7.0

Hardness: 54 – 179 ppm

Diet

Larger Ageneiosus spp. are obligate carnivores by nature feeding on invertebrates and other fishes, and capable of consuming surprisingly large prey.

Newly-imported specimens thus often refuse to accept anything but live fishes though most can be weaned onto thawed frozen whitebait, shellfish or similar once they recognise them as edible. Some individuals even learn to accept dried foods such as pellets designed for carnivorous species.

Like the vast majority of predatory fishes this species should not be fed mammalian/avian meat such as beef heart or chicken, and similarly there is little benefit in the long-term use of ‘feeder’ fish such as livebearers or small goldfish which carry with them the risk of parasite or disease introduction and at any rate tend not have a high nutritional value unless properly conditioned beforehand.

Behaviour and CompatibilityTop ↑

Surprisingly peaceful with anything too large to swallow and can be maintained in a community provided tankmates are chosen with care.

Aggressively territorial or very competitive species should be avoided with the best choices being placid fishes which feed from the substrate such as Geophagus spp., Acarichthys heckelii, comparably-sized doradid or loricariid catfishes and characids from genera like Ctenolucius, Mylossoma or Myloplus.

This species is not aggressive towards conspecifics and exhibits loosely gregarious behaviour in the aquarium given the opportunity, so the purchase of four or more specimens is recommended if feasible.

Sexual Dimorphism

Adult males of Ageneiosus spp. all display marked, seasonal, sexual modifications, with the area between head and dorsal fin origin (nuchal region) exhibiting a much more acute angle than in non-breeding individuals. The maxillary barbel also becomes ossified and extended inbreeding males with tooth-like odontotes apparent on the dorsal and medial surfaces, while the first branched dorsal fin ray is significantly extended giving the fin an enlarged, curved appearance with sharp odontotes appearing along the anterior margin.

The anterior portion of the anal fin in sexually-active males also exhibits seasonal modifications with the unbranched and first few branched rays becoming thickened, elongate and fused together, forming a structural support for the intromittent organ which itself becomes displaced in such a way that the genital pore is situated at the tip of the modified rays. The interradial membranes and surrounding inclinator/erector muscles also become enlarged. In adult females, the unbranched and first few branched anal-fin rays are much longer than the other rays.

Reproduction

Unrecorded in aquaria although some brief reports of apparent courtship behaviour do exist. What is known is that fertilisation occurs internally via the modified genital papillae in males described above, with the ossified and extended maxillary barbels and dorsal fin ray used to court and physically manipulate females.

Since a seasonal spawning strategy is highly likely to be adopted in nature, and induced by the onset of the rainy season, simulation of such via a period of warmth followed by several large, cool water changes may prove useful in captivity.

NotesTop ↑

This species may also be seen on sale as ‘Guyana slopehead catfish’ ‘dolphin catfish’ or ‘hammerhead catfish’. The attractive juvenile patterning is largely lost as the fish grow but this nevertheless remains an impressive predatory species for the larger aquarium.

The genus Ageneiosus was at one point classified in the family Ageneiosidae alongside the genus Tetranematichthys, but this was not accepted by all authors.

The group remains poorly-studied but following the last major revision (Walsh, 1990) A. marmoratus can be told apart from congeners by the following combination of characters: body, head and fin patterning comprising large, irregular, and sharply contrasting black blotches; head large and robust; snout broad and parabola-shaped with a wide gape; caudal fin emarginate with 8+10 principal rays; lepidotrichia of the first dorsal and pectoral fins flexible, segmented and unserrated; gill rakers short and conical; pectoral rays, branchiostegals and ribs relatively numerous.

The genus is separated from other auchenipterids by a combination of absence of mental barbels in adults, and the presence of enlarged, tooth-like odontodes formed by outgrowths of the maxillae on the dorsal margin of the maxillary barbels inbreeding males. The larger-growing members are often utilised as food fishes in their native countries.

The family Auchenipteridae is itself distinguished from all other catfishes by the following: body lacking bony plates except on dorsal surface between head and dorsal fin origin which is covered by a row of such plates joined together and clearly visible beneath a thin epidermis; no nasal barbel(s); adipose fin small, occasionally absent; eye covered by adipose tissue and lacking a distinct orbital rim; anterior anal fin rays enlarged and thickened in adult males; maxillary barbel fits in a specialised groove below the eye when drawn towards the body; maxillary barbel directed laterally and dorsally when drawn into said groove.

References

1. Eigenmann, C. H., 1912 - Memoirs of the Carnegie Museum 5(1): 1-578
   The freshwater fishes of British Guiana, including a study of the ecological grouping of species, and the relation of the fauna of the plateau to that of the lowlands.
2. Ferraris, C. J., Jr., 2007 - Zootaxa 1418: 1-628
   Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types.
3. Reis, R. E., S. O. Kullander, and C. J. Ferraris, Jr., 2003 - EDIPUCRS, Porto Alegre: 1-729
   Check list of the freshwater fishes of South and Central America. CLOFFSCA.
4. Ribeiro, F. R. V. and L. H. Rapp Py-Daniel, 2010 - Neotropical Ichthyology 8(1): 97-104
   Ageneiosus uranophthalmus, a new species of aucheniperid catfish (Osteichthyes: Siluriformes) from river channels of the central Amazon basin, Brazil.
5. Schraml, E., 2004 - Today's Fishkeeper, November 2004: 32-34
   'Gotta Lotta Bottle'.
6. Sullivan, J. P., J. G. Lundberg and M. Hardman, 2006 - Molecular Phylogenetics and Evolution 41: 636–662
   A phylogenetic analysis of the major groups of catfishes (Teleostei: Siluriformes) using rag1 and rag2 nuclear gene sequences.
7. Walsh, S. J., 1990 - Unpublished Ph.D. Dissertation, University of Florida, Gainesville: 1-363
   A Systematic Revision of the Neotropical Catfish Family Ageneiosidae (Teleostei: Ostariophysi: Siluriformes).