Diet and cannibalism in plainfin midshipman Porichthys notatus

Reduced opportunity to feed has long been recognized as a cost of providing parental care. However, few studies have quantified food availability for parents and compared this to the actual diet. The macroscopic and microscopic diversity of potential food items available in the nests of plainfin midshipman Porichthys notatus (Girard 1854) were quantified and compared to items that were found in the digestive tracts of the guarding males. In this species, males occur as one of two possible reproductive morphs: guarder males that care for young, and sneaker males that parasitize the courtship and care of guarder males. Although it was predicted that guarder males would have fewer feeding opportunities due to their confinement to the nest, they in fact had more food items in their guts than did sneaker males and females. Date in the breeding season (a proxy of care duration) and body condition were not correlated with the amount of food consumed by guarder males. The main type of food consumed was midshipman embryos; 69% of all guarder males sampled had cannibalized offspring. By comparing the diet of both sexes and tactics, this study sheds light on some of the strategies designed to cope with the costs of providing parental care.