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In the aquaculture industry, 60-70% of the production cost comes from fish feeds; therefore, choosing a commercial feed for cultured fish must not be taken for granted. 

Nutrient Requirements

The nutrient requirement of the fish to be fed must be known first and should be comparable with the nutritional value of the feed. Note that some fish may differ in their nutrient requirements in some areas of their life stages.

Every fish species has their own required nutrients (% protein & % lipid/fat)  in order to grow and function well. To support optimum growth of fish in aquaculture, especially if the fish are being fed with artificial feeds only (meaning fish solely rely on feeds given to them by fish farmers), the feeds that should be given to them must meet the requirement of the fish for protein and lipid. If we already know the nutritional requirements of the fish then we can purchase a feed based on that data. Protein sources in fish feed for example could be animal, poultry by-products or plant protein sources like fish meal, insect meal, feather meal, soybean meal and corn gluten meal. Lipid sources are oils which could be fish oil, plant oils or combination.

Usually commercial feeds put labels on their packaging which includes values of proximate composition such as protein, lipid, moisture and ash.

Consider the following scenario: Rainbow trout need 40-42% protein and 12-14% lipid/fat.

Based on this information, we should buy a feed that contains 40-42% protein and 12-14% lipid/fat. These are the values we should check on the label of the container of the feeds we will buy in the market or feed mill.

Also we must take note that, in some fish at different life stages, their nutrient requirement differs. Juvenile fish require higher protein than adult ones since they need more protein for growth. In this case,  there is specific feed for juveniles and another one for adult fish. Sizes of pellets also differ based on the life stages of fish.

Choosing the Optimal Feed to Avoid the Protein Sparing Effect

Choose the feed which shows a label with proximate composition in it. Proximate composition must include values pertaining to macronutrients such as crude protein, fat/lipid and also moisture and ash.

Crude lipid/fat together with carbohydrates are energy sources. In choosing feeds to buy for the cultured fish, the values  for lipid must be the same with the requirement level of the fish to avoid protein sparing effect. Protein must be reserved for growth and cell repair and not as an energy source. Energy sources are lipids and carbohydrates. However, if the lipid content of the feeds is below the requirement of fish, some proteins will be converted to lipids to produce energy. We should avoid this from happening. Thus,  if the lipid requirement of the fish is 15% then the feeds you must buy should also contain 15% lipid.

Protein sparing effect happens when the lipid/fat content of the feed is not enough or below the requirement of the fish.

If that happens, in order for the fish to function normally, protein will be  used and converted to lipid to be used up as an energy source. In that scenario, protein will be spared for lipid. This means, protein in feeds which should be allocated for fish growth has been reduced thus fish growth will be negatively affected. We do not want this to happen in our cultured fish, this would mean longer culture period since fish are not growing at an expected time frame; of course this would also mean economic loss in the business aspect.

Also, moisture must be below 12% so as not to allow microorganisms to grow in the feed while in the feed/storage room. Ash must also be low because higher ash would mean low digestibility of the det. 

Managing Your Feed

For feed management, make sure to store your feeds in a dry cold room (below 16°C) and must be placed away from the wall to avoid rodents and insects' manifestation as well as possible moisture absorption coming from the wall of the storage room.

Observe first in first out basis. The first batch of feed bought must also be the first batch to be used to feed the fish.  For example in your schedule, you specified to order feeds every 3 months. In January 2020 you will buy 10 sacks of trout feed so that is the first batch (first in) of orders and it must also be the first ones to be used up (first out). Then, the next orders will be on March 2020 (2nd batch). Before using the 2nd batch of feeds, make sure to use up first the 1st batch of feeds. Feeds must be used up before it reaches 6 months after buying.

Rena Santizo-Taan

PhD in Fisheries Nutrition

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