Taxonomy & naming
Mugilogobius rexi was described by Larson (2001), and the Catalog of Fishes gives the type locality as the mouth of the Batuopa River south of Timampu on Lake Towuti. The name is listed as valid in the Catalog.
Morphology
FishBase gives a maximum of 1.5 in SL. As in other gobies, the pelvic fins are fused into a sucker disc. Colour in life has not been compiled in the sources used here.
Habitat
Lake Towuti is the largest of the Malili Lakes, a deep, clear, alkaline lake in southern-central Sulawesi. FishBase describes the species as hovering just above the substrate in a slightly diagonal posture, in at least a metre of water over silty bottom, near clumps of aquatic plants and the freshwater mangrove Barringtonia racemosa. The genus is noted as facultatively air-breathing. Measured water parameters have not been published.
Feeding
Diet has not been described for this species; small invertebrates are the usual food of the genus.
Mating
Mating has not been described for this species.
Breeding
Breeding has not been described for this species.
In the aquarium
Husbandry has not been documented. A lake endemic from clear, hard, alkaline, stable water should be kept in water of that character, not in soft acidic conditions, with plants and fine substrate to match its habitat.
Conservation
The IUCN lists Mugilogobius rexi as Near Threatened, meaning it is close to qualifying for a threatened category. The species is restricted to a single lake system, and the Malili Lakes are affected by introduced fishes, mining and catchment change.