A study on the Trahira, or wolffish, Hoplias malabaricus, has shed new light on how the species breeds and cares for its offspring.
A group of ichthyologists from Brazil studied the toothy erythrinid predator living wild in the southern Pantanal in the Brazilian state of Mato Grosso do Sul, and found that the when the species breeds, it is usually the male who looks after the brood, although biparental care is sometimes also seen.
Prado, Gomiero and Froehlich, who announced their findings in the latest issue of the Brazilian Journal of Biology, observed 11 nests and found that eight were guarded by the male, while three were guarded by both parents - leading them to conclude that parental care is primarily paternal.
The study showed that H. malabaricus in the Miranda river spawned around thirty days after the flood waters arrived. The fish breeds in clean, shallow water at depths of just 12-24cm and constructs a nest by excavating a 10cm wide depression in the bottom sand near aquatic vegetation. The number of eggs recorded was very high, with 6000-12,000 yellow eggs laid in a compact mass in each nest.
During spawning, the fish positioned their bodies side by side while facing in the same direction, while the male tried to push its vent towards the females vent. When the eggs had been deposited, the female left the nest, while the male remained to guard the clutch.
As you would expect from a species with a reputation for being aggressive, the males defended the clutch ferociously from both other fish and the scientists studying their reproduction.
The Hoplias genus is one of three genera in the Erythrinidae family - the other two being Hoplerythrinus and Erythrinus. All are external fertilising egg layers which build nests and exhibit some form of nest-guarding, usually by the males.
For more details on the study see the paper: Prado CPA, Gomiero LM and O Froehlich (2006) - Spawning and parental care in Hoplias malabaricus (Teleostei: Characiformes: Erythrinidae) in the southern Pantanal, Brazil. Brazilian Journal of Biology, 66(2B): 697-702.