The importance of brood size, offspring age, and male size for parental care behaviour was studied in the common goby, Pomatoschistus microps. In field observations, the aggression of nest guarding males was measured as attacks towards a finger when disturbing the nest. Attacking males had larger and more developed clutches compared to non-attacking males, but did not differ in body size. In another set of observations nest guarding males were exposed to a predator (eelpout, Zoarces viviparus) and subsequently chased away from their nests. Time away from the nest decreased significantly with egg developmental stage, i.e. with the time the male had spent guarding a particular brood. However, no correlations with male body length or numbers of eggs in the nest were found. We conclude that male common gobies evaluate future reproductive success by using brood age and brood size as cues for making decisions about risk-taking and aggressive behaviour during parental care.
The effects of predation risk on the reproductive behaviour of male and female sand gobies, Pomatoschistus minutus, were investigated in two separate aquarium studies. In the presence of a predator (cod, Gadus morhua), males decreased their courtship activity while females did not alter their level of activity. In the second study, there was no difference between treatments (with and without predator) in the time from when a female was presented to a male with a nest until spawning took place or in the amount of eggs laid. However, pre-spawning behaviour differed between the two treatments. When the cod was in sight, both males and females burrowed in the sand more often. In the absence of a predator, pairs spent longer together in the nest before spawning started, and females also inspected the nest alone, which never happened during predator presence. Hence, both sexes make trade-offs between predator avoidance and behaviours associated with mating. Females, however, seem to take higher risks during the courtship phase in order to find a partner compared to males.