Genetic Assessment of the Mating System and Patterns of Egg Cannibalism in Atka Mackerel

The mating system and patterns of gender-specific egg cannibalism in Atka mackerel Pleurogrammus monopterygius were examined through genetic parentage analysis of embryos in egg clutches produced in captive and wild populations. Like other hexagrammid fishes, Atka mackerel exhibit polygynandry, which is characterized by serial matings by both genders within a breeding season. Most matings in captivity were pairings of females with nest-attendant males, although parentage analysis of clutches produced in a small tank with limited nesting substrate revealed that 31% contained contributions by non-nest-guarding males. In contrast, all egg clutches produced in a large exhibit tank were sired by guardian males. Multiple parentage, sometimes involving both genders, was detected in 35% of egg clutches collected in the field or retrieved from the guts of adult male and female cannibals. Half-sib and unrelated full-sib embryos were found in several putative clutches, indicating that the reproductive output from multiple males and females may be combined sequentially and fused into a single clutch. These results suggested that nest takeovers, combined with alloparental care of existing broods, represent common reproductive tactics in males. Egg cannibalism is a significant seasonal factor in the diets of male and female Atka mackerel. Analysis of loose eggs and partial egg clutches ingested by 4 female and 15 male cannibals showed that nearly all conspecific predation represented heterocannibalism. One instance of partial filial cannibalism was documented in a male that was one of multiple sires for the clutch.