Feeds and feeding for fish farming

Fish nutrition is one of the most important aspects of fish farm management; you cannot be successful as a fish farmer if you fail on this point.  Feeding typically represents around 50% of the operational costs on a fish farm, so an inefficiency here results in double the impact on the bottom line.
 
What do we feed fish?
Fish feed is made of a range of potential products.  Traditionally, fish meal and fish oil were primary components, but due to overfishing and environmental concerns, these constituents have been replaced by farmed products including soya, wheat, maize, planktons, algae and insect meal.  It is extremely important to ensure that feed composition contains the correct amino acids in the appropriate ratio for the fish species being produced as these operate as building blocks within the fish cells.  Digestible fats are also essential in fish feed because they provide energy and play a role in a host of physiological activities.  Aquaculture pellets are extruded as this ensures a water stable product in which the components are held together long enough to be ingested by the fish.  Carbohydrates are included in the recipe as the cooking causes them to expand, providing the low density required for the pellet to float, and to become sticky, thereby holding the ingredients together.
 
Fry and fingerlings require greater quantities of protein than do growout size fish of the same species, so juvenile diets include a higher protein content than growout diets.  The size of the feed must also match the size of the mouth of the fish that is eating it, and as such, high protein hatchery diets are supplied as micropellets or crumble.  As the fish grow the pellet size increases and protein content decreases, and due to the relatively high cost of protein, the growout feed price is also lower than that of the hatchery feeds.
 
How often do we feed fish?
Small fish grow extremely quickly and require regular, small meals to fuel this rapid metabolism.  Hatchery fish are typically fed 5 times daily or even more frequently, starting as early as possible each day and feeding until the last possible time.  Growout fish are satisfied with 3 daily meals, although species does play a role in this generalisation.
 
How do we feed fish?
Research shows that the target is to feed fish to about 80% of the satiation requirement.  At this point they have taken in sufficient nutrients to optimally fuel their metabolism and growth, but beyond this point the feed conversion efficiency decreases.  Practically we achieve this by feeding until the aggression with which the fish are feeding decreases sharply, and at this point we stop feeding, the meal is over.
 
Managing feed usage
The exact mass of feed given daily should be recorded, as per individual tank, pond or cage protocol.  Over a fixed period, typically a month, the mass of feed given to that culture facility is compared to the growth achieved by those fish, enabling the farmer to determine how efficiently feed was converted into growth.  This matrix is known as the Feed Conversion Ratio (FCR) and is one of the fundamental records and analyses that is conducted as part of the management of a fish farm.  For tilapia the FCR should be around 1:1.5; in other words, 1.5kg of feed is required to achieve 1.0kg of growth.  If the FCR increases, i.e. more feed is required to achieve the 1.0kg of growth, this indicates a problem somewhere in the production process and the manager can systematically investigate until the problem and an appropriate solution are found.
 
Feed quality
As part of the assessment to improve FCR the manager will consider the quality of the feed being used and compare this to alternative options.  The general principle is to buy the best quality feed available.  Better feed should give faster growth, resulting in less feed being utilised, and usually results in less faecal waste, which has positive implications for water quality and the downstream environment.  Check carefully though that the improved FCR does in fact justify the increased feed cost in financial terms.
 
Feeding fish correctly is a foundational skill that every farmer needs to master.  Fish feed is the biggest single operational cost on a fish farm, so be sure to optimise the conversion ratios to remain profitable.