Taxonomy & naming
Chaetostoma trimaculineum was formally described by Lujan, Meza-Vargas, Astudillo-Clavijo, Barriga-Salazar, and López-Fernández in 2015. The Catalog of Fishes (Eschmeyer, CAS) recognises this as a valid species within the large and diverse genus Chaetostoma, subfamily Hypostominae, family Loricariidae. Voucher specimens are deposited at the Royal Ontario Museum (ROM 93894, from the upper Santiago River, Ecuador) and Auburn University Museum (AUM 45524, from the middle Marañón River, Peru).
Phylogenetic analysis by Meza-Vargas et al. (2022) placed C. trimaculineum within a polytomy that includes C. breve, C. dermorhynchus, C. dorsale, C. formosae, C. orientale, and an undescribed Orinoco species. Biogeographically it is considered part of a cluster of seven Chaetostoma species centred on the Huallaga River drainage of central Peru, a hotspot for Andean loricariid diversity.
Morphology
Adults reach up to 6.5 in standard length (SL), making C. trimaculineum a moderately large member of its genus. The body follows the typical Chaetostoma plan: dorsoventrally flattened with robust bony scutes, a broad depressed head, and a ventrally positioned sucking disc mouth well adapted to attaching to smooth rock surfaces in fast current.
The diagnostic character that gives the species its name is immediately apparent: three to four linear rows of distinct, round, nostril-sized black spots run along the trunk plates and extend onto the head. These spots are clearly defined against the lighter background coloration and are of a consistent, almost measured regularity. Four branched anal-fin rays are recorded. This black-on-pale spot pattern contrasts directly with the pattern of the closely related and recently described Chaetostoma sacramento, which bears white spots on a dark background.
Habitat
Chaetostoma trimaculineum is known from the upper Santiago River in eastern Ecuador and the middle Marañón River in northern Peru — both fast-moving Andean and sub-Andean river systems draining the eastern slopes of the Andes into the Amazon basin. These rivers are characterized by high dissolved oxygen from turbulent flow, cool-to-moderate temperatures influenced by Andean altitude, and substrates of exposed bedrock, cobble, and boulder.
Like other members of the genus, C. trimaculineum is a rheophile: its flattened body and adhesive disc mouth are adaptations to holding position in fast current, and it almost certainly inhabits riffles and rapids where water is cleanest and most oxygenated. No formal water parameter data from collection sites have been published for this species. General conditions inferred from similar Andean Chaetostoma habitats suggest cool, clean, well-oxygenated water with moderate-to-low conductivity.
Feeding
As with all Chaetostoma, C. trimaculineum is primarily an aufwuchs and algae grazer. The ventral sucker mouth, equipped with fine teeth suited to rasping, is pressed against rock surfaces to scrape periphyton — the biofilm of algae, diatoms, and associated microorganisms — from boulders and bedrock. In the fast-flowing rivers it inhabits, this food source is continually replenished by turbulent, nutrient-bearing water.
In aquarium care, the diet should emphasise algae-based foods: spirulina wafers, high-quality algae discs, blanched vegetables such as courgette (zucchini) and cucumber, and occasional pieces of softwood for biofilm. Animal protein should form only a minor supplement. Consistent access to surfaces colonised by natural algae or biofilm, whether on rocks or driftwood, supports both nutrition and natural foraging behaviour.
Mating
No specific courtship observations for C. trimaculineum have been published. Based on the reproductive biology of the genus broadly, males of Chaetostoma typically establish territories around suitable spawning sites — crevices, caves, or undercut rock faces in areas of moderate to strong current. Males develop interopercular odontodes (cheek bristles) during the reproductive season, which are used in male-to-male displays and in tactile courtship. Gravid females appear noticeably broader-bodied than males of equivalent size.
Breeding
No breeding records for C. trimaculineum in captivity are known from the available literature. Chaetostoma species generally follow the loricariid cave-spawning mode with paternal brood care: eggs are deposited in a sheltered cavity and the male fans and guards them until hatching. Replicating the cool, highly oxygenated, fast-flowing conditions of the species' native Andean rivers would be the logical starting point for conditioning attempts, including strong water flow from powerheads or circulation pumps and a gradual temperature drop to simulate seasonal cues.
In the aquarium
Chaetostoma trimaculineum's rheophilic origins mean that water quality and oxygenation are non-negotiable. Strong circulation, high dissolved oxygen, and pristine water conditions — zero ammonia and nitrite, low nitrate — are the fundamental requirements. Temperature should be kept on the cooler side relative to typical tropical community tanks, reflecting the species' Andean provenance.
The aquarium should be furnished with smooth and rough rocks, flat stones, and slate to provide both grazing surfaces and hiding spots. Powerful filtration and regular water changes are essential; the fish will not tolerate stagnant or poorly oxygenated water. At up to 6.5 in SL this is not a small fish — a tank of at least 40 US gal with robust filtration is appropriate for an adult.
Chaetostoma are generally peaceful toward other species but may be intolerant of conspecifics or similar-looking plecos in confined spaces. Tankmates should be chosen from species tolerant of the same strong-current, well-oxygenated conditions — hillstream loaches and robust rheophilic danionins can coexist, though typical soft-water community fish may find the required current levels uncomfortable.
Conservation
Chaetostoma trimaculineum has not been assessed by the IUCN Red List and carries the status Not Evaluated. The species was described in 2015 from a limited number of voucher specimens representing two river systems — the upper Santiago in Ecuador and the middle Marañón in Peru — and its full range and population status have not been formally surveyed.
The eastern Andean slopes that this species inhabits face ongoing pressures from deforestation, agricultural encroachment, and gold mining, all of which cause sedimentation that can degrade the clear, fast-flowing habitats on which rheophilic loricariids depend. A formal IUCN assessment drawing on targeted field surveys would be a valuable step toward understanding whether this recently described species faces any meaningful conservation risk.