In aquaculture, feed is amongst the most important factors that can impact fish growth rates. Most commonly found in pellet form, feed must be able to provide all of the required nutrients, offer the highest possible conversion rates, and of course be economically viable for commercial use. There are many aspects to creating the optimal pellet - including the pellet size.
As a general rule of thumb, pellet are generally considered optimal at sizes 25% – 50% of the fish’s mouth width. However, as with anything, the relationship between pellet size and growth rate is not entirely straight forward.
Pellet size is clearly important from one key physiological perspective – the individual’s mouth. Give a fish a pellet larger than its gape, and not only may it have trouble eating that pellet, but it could even choke. The way a fish eats is also an important factor in considering what size pellet to offer. Gilthead sea bream (Sparus aurata), for example, essentially “chew” large pellets before swallowing them. During chewing, some feed is lost into the water, and with it precious nutrients that could otherwise be used for growth. Recent work from scientist Mateo Ballester Moltó (Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario, Spain) demonstrated that feeding pellets smaller in size than manufacturer recommendations to gilthead sea bream reduced the need for chewing, reducing the loss of up to 42 grams of feed per kilogram of fish.
Smaller pellets may seem the obvious answer, but they also have their issues...
This article was written for (and can be read in full on) The Fish Site.