Why is male parental care especially common among some fish?

In the context of animal social behavior, male parental care is notably more common in fishes than in many other animal groups, though it remains a subject of ongoing research to fully understand why the cost-benefit ratio favors males in these specific instances.1

Several factors contribute to this prevalence:

• External Fertilization: Male parental care is most common in fish species that utilize external fertilization. In many of these species, males release sperm after the female has deposited her eggs, which may place the male in closer proximity to the eggs at the time care is required.1
• Proximity and Timing: The likelihood of a parent providing care is often linked to their proximity to the offspring. If a female lays eggs immediately after copulation, the male is often already present, making it more feasible for him to assume guarding duties.1
• Evolutionary Trade-offs: Because parental care is costly, a conflict of interest exists between the sexes. In some species, the ratio of benefits to costs for males—such as protecting a nest or brooding young in the mouth—is apparently higher than that of females, leading to the evolution of male-only care in groups like sea horses and giant water bugs.1

While some hypotheses suggest that the order of gamete release dictates which sex deserts, this does not fully explain why males provide care even when gametes are released simultaneously. Ultimately, the specific environmental and physiological constraints of each species play a critical role in determining which parent provides care.1