Have you ever had trouble feeding or keeping baby fish? Mortality in marine larval fish (such as clownfish) is high for many reasons, but a main culprit is the lack of appropriate food. In the wild, the diets of larval fish are mainly made up of copepods, which with their different forms provide suitable prey as a fish grows. Although they are the prefered prey type of many larval fish, copepods are some of the most evasive zooplankton.
Copepods possess sensors on their antenna which are sensitive to movement in the water, providing them with a warning system for approaching predators and allowing them time to escape. This escape response is the least developed in the nauplius form and becomes more effective as the copepod reaches the copepodid and adult forms.
As fish larvae grow, their feeding success increases as they are able to attain faster swimming speeds, with their approach being less likely to trigger an escape response in their prey. Because feeding efficiency is low during a fish’s first few days as a larvae and copepods have a good escape mechanism, higher concentrations of copepods may be required to provide nutrition to young fish. The less mobile, smaller rotifers help to supplement food intake during this stage of the fish’s life.
Clownfish hatch carrying a yolk sac which provides them sustenance for their first three days while their capture rates of prey are low The larval phase of clownfish lasts for about two weeks, during which they feed on copepods, rotifers, and phytoplankton, with their predatory success increasing with age as they are able to incorporate larger and more evasive prey, while also capturing previous prey types with more efficiency. By eight days post hatch, clownfish larvae have incorporated all three copepod types into their diet, preferring larger copepod types as their own bodies grow larger.