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The Current State of Plant-Based Proteins in Aquaculture Feed

Changing global demand for fishmeal affects its availability for use as an ingredient in diets for various aquaculture species. Such uncertainty cannot always be tolerated, so suitable alternative sources of protein are being investigated and used. The most common alternative protein sources are plant-based proteins such as soybean meal.


Anwar HasanJustin Tan

+ Predicted levels of fishmeal use in aquaculture feeds will fall from up to 50% inclusion as seen in 1995 to below 10% in various species by 2020.
+ Plant-based protein sources are still the preferred alternatives for replacing fishmeal in aquaculture feeds.
+ The limitations of using plant-based protein sources such as mycotoxin contamination and high phytate content must be managed to maintain health and performance.

Changing global demand for fishmeal affects its availability for use as an ingredient in diets for various aquaculture species. Such uncertainty cannot always be tolerated, so suitable alternative sources of protein are being investigated and used. The most common alternative protein sources are plant-based proteins such as soybean meal.

Using plant-based protein in place of fishmeal comes with some challenges, including:

  • amino acid profile
  • phytate presence
  • mycotoxin contamination

Various functional feed additives are now able to reduce or eliminate these challenges, making plant-based protein sources a viable solution for aquaculture producers.

The aquaculture industry uses 70% to 80% of all fishmeal produced

Aquaculture production

The FAO reported in its ‘The State of World Fisheries and Aquaculture, 2018’ review that total global aquaculture production in 2016 was 80 million metric tons (MT), with 61.9 million MT coming from finfish and crustaceans (FAO, 2018). This did not include aquatic plant production for that year which was approximately 30.1 million MT. The global capture fisheries production in 2016 was 90.9 million MT, slightly lower in comparison to the previous two years.
 

Fishmeal production expected to rise

World fishmeal production in 2015 was 4.7 million MT, down from a high of 6.8 million MT in 1988; production has decreased each year since. However, it is predicted that in 2022, global fishmeal supply will rise to 5.4 million MT (Figure 1).

The aquaculture industry uses 70% to 80% of all fishmeal produced. If predictions are correct and total fishmeal production reaches approximately 5 million MT in 2020, this suggests that 3.5 million MT of fishmeal will be used in aquaculture in 2020.

World fishmeal production in 1988, 2015 and predicted level in 2022
Figure 1. World fishmeal production in 1988, 2015 and predicted level in 2022
For some aqua species, diets are already formulated without any fishmeal

Inclusion rates decline

Tacon and Metian (2008) predicted that the use of fishmeal in aquaculture feeds will drop to below 10% in various species (Figure 2). Carp, catfish and tilapia diets will contain 1% to 2% fishmeal whereas penaeid shrimp, marine fish, salmon and trout will contain 5% to 10% fishmeal. For some aqua species, diets are already being formulated without any fishmeal.

Fishmeal has become a strategic raw material in aquaculture feeds. The demand for fishmeal and fish oil for aquaculture use is predicted to increase, consequently reducing its availability and increasing its price.

For decades, studies on fishmeal replacements have been conducted in many aquaculture species. These studies assess not only the digestibility of feed and effects on growth with amino acid supplements, but they also assess health status and flesh quality.

Percentage of fishmeal used in aquaculture feeds from 1995 to 2020
Figure 2. Percentage of fishmeal used in aquaculture feeds from 1995 to 2020.
Source: Tacon & Metian, 2008

Fishmeal substitutes

There are several factors to consider when using feed ingredients to replace fishmeal including:

  • Nutritional value
  • Customer acceptability
  • Availability
  • Price or cost
  • Effects on growth
  • Effects on health status

Figure 3 shows a number of feed ingredients which can substitute fishmeal. 

Alternative ingredients to substitute fishmeal
Figure 3. Alternative ingredients to substitute fishmeal
Plant-based protein sources are still the preferred alternatives for replacing fishmeal in aquaculture feeds.

Plant-based ingredients

Plant-based proteins are widely used as ingredients for aquaculture diets. Different types of plant-based ingredients have been assessed in a number of nutritional studies for aquaculture, including many kinds of legumes, cereal grains and leaf meals. Plant-based ingredients are used not only as protein sources but also for other nutritional and functional requirements, for example starch used as a binder.

Soybean meal is a widely used plant protein source in the aquaculture industry and is the most-studied ingredient in terms of fishmeal replacement. Other soybean-based products are shown in Table 1.

Table 1. Other soybean-based products and their crude protein contents

Soybean productPercentage crude protein
Fermented soybean48%
Defatted soybean meal50 - 54%
Soybean protein concentrate (SPC)67 - 72%
Soy protein isolate (SPI)90 - 92%

Source: BIOMIN, 2019

These other soybean-based products can be used to reduce fishmeal inclusion, either on their own or in combination with other plant-based ingredients such as vegetable blends, with good results. However, the soybean meal market is unstable as there are many other industrial uses that can increase demand and therefore prices. As such, focused research efforts are ongoing to assess the suitability of other plant sources.

Limitations of plant-based ingredients

There are several limitations and challenges to using plant sources in aquaculture diets including:

  • Anti-nutritional factors (ANFs)
  • Amino acid profiles
  • Fatty acid profiles
  • Mineral profiles
  • Palatability
  • Mycotoxin contents

All these factors can affect growth and health status, even causing high mortality in extreme cases.

Feed additives are one solution to reduce the negative effects of plant-based proteins.
Amino acid barrel theory
Each essential amino acid represented by a slat of a barrel, making up the amino acid barrel to illustrate limiting amino acids

Amino acid profile

The essential amino acid profile is the main concern when using plant-based proteins in aquaculture feed. Any imbalance in essential amino acids resulting from plant ingredient inclusion can negatively affect fish and shrimp growth. Figure 4 illustrates the amino acid barrel theory. When making a barrel, each of the staves must be the same length to ensure the barrel can be filled with water. If one of the staves is too short, the barrel can only be filled to that level. This is also true of amino acid uptake. Each of the essential amino acids (staves), must be provided by the diet. But if one amino acid is insufficiently supplied (a shorter stave), that will limit uptake of all the other amino acids, regardless of their quantity. 

  • Crystalline amino acids have shown positive effects on managing the lack of essential amino acids in plant ingredients. Another strategy is to use the optimal combination of raw materials. For instance, soybean meal or soy protein concentrate is higher in lysine, and corn gluten meal is higher in methionine, or methionine and cysteine.

Molecular structure of phytate with the location of chemical components indicated around the central inositol ring
Molecular structure of phytate with the location of chemical components indicated around the central inositol ring.
Source: BIOMIN

Phytate

Phytate is a common constituent of plant-derived fish feed ingredients. Phytate is also known as phytic acid or inositol polyphosphate and is formed during the maturation of plant seeds and grains. Some major concerns surrounding the presence of phytate in feed are its negative effects on growth performance, nutrient and energy utilization, and mineral uptake.

  • In terms of managing phytate, there have been many studies using dietary phytase enzymes to manage the negative effects of phytate in fish. One such study reported that the use of phytase can increase the total digestibility and apparent digestibility coefficient of protein, and the apparent digestibility of phosphorous from soybean-based feed for Asian seabass.

Interacting factors influencing the effects of mycotoxins in fish and shrimps
Figure 6. Interacting factors influencing the effects of mycotoxins in fish and shrimps

Mycotoxins

Mycotoxins are secondary metabolites produced by fungi, commonly referred to as molds. They are produced by fungi when they grow on agricultural products before or after harvest or during transportation or storage. Since plant-based ingredients are more susceptible to mycotoxin contamination, the impact of mycotoxin contamination will increase as inclusion levels of plant-based ingredients in aqua feeds goes up (Figure 6).

Most of the mycotoxins that have the potential to reduce the growth and health status of shrimp and other farmed animals consuming contaminated feed are produced by Aspergillus, Penicillium and Fusarium spp. These toxic substances and their effects are shown in Table 2.

Table 2. Origins of mycotoxins and their effects

Mycotoxin effectMycotoxin types
CarcinogenicAflatoxin B1
Ochratoxin A
Fumonisin B1
EstrogenicZearalenone
NeurotoxicFumonisin B1
NephrotoxinOchratoxin
DermatotoxicTrichothecenes
ImmunosuppresiveAflatoxin B1
Ochratoxin A
T-2 toxin

Source: BIOMIN, 2019

The consequences of mycotoxin contamination in aquaculture feeds are largely unknown due to the lack of information on the impact of different mycotoxins in crustacean culture. Although information is limited, several studies have been conducted on the toxicity of mycotoxins in aquatic animals including shrimp.

Aflatoxins

It has been reported that dietary aflatoxin B1 (AFB1) adversely affected growth performance, feed conversion, apparent digestibility coefficients, and caused physiological disorders and histological changes, in particular to hepatopancreatic tissue. Another study reported that AFB1 levels below 20 ppb (20 µg/kg) caused reductions in weight gain and slightly increased mortality, after only 10 days.

Fumonisins

Another study reported the negative effect of fumonisin B1 (FB1). Total hemocyte count and phenoloxidase activity decreased by the 18th day in shrimp exposed to FB1 on tested dosages of 0, 0.5, 0.75 and 1.0 μg/g of FB1. Marked histological changes in the hepatopancreas of shrimp fed diets containing FB1, at all the FB1 levels tested, as well as the presence of necrotic tissue were observed.

 

  • As for managing the mycotoxin risks in aquaculture feed, some studies reported the benefits of using mycotoxin binders or deactivators. In shrimp, a study reported that mycotoxin binders could manage the negative effects caused by feeding aflatoxin-contaminated diets to white shrimp (L. vannamei) juveniles.

Managing the limitations of plant-based ingredients

Feed additives are one solution to reduce the negative effects of plant-based proteins. Many studies have been conducted to prove that the use of feed additives increases performance.

With so many ways to manage the limitations of including plant-based ingredients in aquaculture feed, the risks of replacing fishmeal have been reduced significantly in some species without any significant impact on growth performance, mortality and health status.

References

Food and Agriculture Organization of the United Nations (FAO). (2018). The state of world fisheries and aquaculture. [Online]. Available from: www.fao.org/3/i9540en/I9540EN.pdf. Accessed 07.11.19.

Tacon, A.G.J. and Metian, M. (2008). Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: Trends and future prospects. Aquaculture. 285 (1-4). 146-158.