Marine larval fish production: a nutritional perspective

Introduction Many of the marine species that are currently being produced on a commercial basis are members of the group of fishes known as pelagic spawners. The reproductive strategy employed by these fishes involves the production of large numbers of small, buoyant eggs which, after being released into the water and fertilized, drift freely in surface currents with no further parental attention. Newly hatched larvae typically carry an elliptical yolk sac containing an oil globule. Although, the yolk and oil globule function as nutrient stores for further development of the newly hatched larvae, these stores tend to be small and influenced by a variety of factors. Upon initiation of feeding the larvae often have minimal nutrient reserves and a small mouth gape which limits the type of prey that they can consume. As a result, larvae do not do well on foods of sub-optimal nutritional value. Survival through the larval stages is quite tenuous and is generally considered the most critical period affecting marine fish recruitment as well as aquaculture development. Finding prey items of appropriate size and nutritional characteristics is a difficult challenge in the wild and one of the primary concerns in the culture of larvae. Successful feeding is dependent on larvae locating appropriate food items, ingesting the items and assimilating nutrients from the food source. This process is complicated by a number of factors which include: 1) limited and variable energy reserves giving a relatively small window of opportunity prior to starvation, 2) small size of the larvae reducing the effective distance the larvae can travel, as well as the size of the particle that can be consumed, 3) extremely fast growth rates and minimal nutritional reserves, and 4) undeveloped