Trace mineral nutrition in fish and shrimp – working towards optimum performance and sustainability in a rapidly evolving industry

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Aquaculture is one of the fastest growing agricultural industries, particularly in Asia. Nutrition, specifically trace minerals, is just one of several key aspects that one must consider in successful, profitable, and sustainable farm management.

Trace minerals, which are required in ‘trace’ amounts, are essential elements that have roles in several physiological and metabolic processes in fish and shrimp. Of particular importance are copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and selenium (Se), which all contribute to maintaining health, fertility, and immunity, as well as improving growth rate and feed efficiency. A summary of the specific functions of these trace minerals is provided in figure 1.

Figure 1: Key trace minerals and their physiological and metabolic benefits in aquatic species

Although the benefits of trace minerals in aquatic nutrition are clear, the exact dietary requirements can be a murky area.

Trace mineral requirements in aquaculture – what needs to be explored?

The exact trace mineral requirements for aquaculture are still being explored and are hence a subject of debate.

According to Lall (2007) a fine balance of trace mineral nutrition is required to maintain homeostasis (maintenance of the internal environment of the animal). Excess mineral intake, either dietary or environmentally, can cause toxicity, while a deficiency can compromise immunity, therefore increasing susceptibility to disease. Lall (2003) has recommended the following ranges of dietary trace minerals in fish (Table 1).

Table 1: Recommended ranges for trace mineral supplementation in fish (Lall, 2003).

However, from the perspective of the National Research Council (NRC), knowledge on trace mineral requirements for farmed fish and shrimp is lacking (NRC, 2011). As a result, their recommendations outlined in Table 2 and 3 appear incomplete. It is worth noting that the NRC provide no differentiation between trace mineral source (organic versus inorganic), which has major influence on mineral absorption, interaction, bioavailability and dietary inclusion rates.

Table 2: NRC recommendations (2011) of mineral requirements for freshwater fish  

Table 3: NRC recommendations (2011) of mineral requirements for shrimp  

Form affects function – feed ingredient sources and mineral interactions

Trace mineral composition and bioavailability can differ markedly in aquatic feed ingredients and complete feeds due to high amounts of fish meal and marine by-products present (Lall 2007; McDowell, 2003). As a result, some trace mineral levels in feed can be exceptionally high. Excess dietary minerals can affect the absorption and bioavailability of other trace minerals within digesta. One example is excess dietary phosphorus which can interfere with the absorption of zinc (Lall 2003).

Although fish meal is considered an adequate source of dietary minerals, supplementation of fish meal-based diets with certain trace elements is necessary for optimum growth and bone mineralization. In diets containing high levels of plant protein, mineral supplementation is necessary to improve growth and bone development in carnivorous salmonid and marine fish.

An example of the relationship between mineral bioavailability and dietary composition is zinc versus protein source. Zinc is better absorbed from animal protein sources than from plant sources such as cereals. Plant feedstuffs contain several substances such as phytate, which can bind to zinc and make it unavailable for absorption in a phenomenon known as antagonism – or negative interactions – between feed components.

If zinc is not supplied at an appropriate level, whole body, intestinal and bone zinc cannot be maintained. A continuous supply of dietary zinc is therefore required. The same holds true for iron –  bioavailability of iron is influenced not only by its chemical form, but also by interactions between other dietary components such as ascorbic acid, which enhances iron absorption, or tannic acid, which can decrease it.

One way that nutritionists counteract antagonistic interactions is to incorporate a mineral program that includes highly stable trace minerals, which must be from an organic source.

Organic trace minerals – how mineral form influences function and productivity

Supplementing aquatic feed with trace minerals in an organic form, such as BIOPLEX^® mineral proteinates and SEL-PLEX^® organic selenium-enriched yeast (Alltech, Inc.), reduces antagonism with other dietary components such as phytates. The chemical structure of BIOPLEX proteinates confer high stability, which results in a trace mineral that is less likely to interact and bind with feed components and more likely to be absorbed and contribute to growth, immunity, and fertility.

Research into the efficacy of BIOPLEX and SEL-PLEX have demonstrated higher bioavailability compared to their inorganic counterparts and warrants the use of lower dietary inclusion rates via reduced wastage of unassimilated minerals.

Rider and Davies (2007) investigated organic zinc and selenium in fish diets and established that organic trace minerals are far more superior in terms of bioavailability and performance when compared to inorganic sources.

Organic trace minerals have several positive effects on animal health and performance, such as increased disease resistance, growth and improved feed conversion (FCR). Such effects have significant benefits in aquaculture, including decreased incidence of disease, better production, increased fillet quality, and increased water quality from less mineral wastage.

The influence of BIOPLEX and SEL-PLEX organic trace minerals on the productive performance of shrimp and fish

Immunity, survivability, and growth

[1] BIOPLEX minerals (zinc, manganese, copper, iron and cobalt) are trace minerals that are bound to amino acids and a range of peptides and are co-factors in enzymes critical to the animal’s defense system, growth and reproduction.

[1] SEL-PLEX by Alltech, is a proprietary form of selenium-enriched yeast and is the first European Union-approved and only U.S. Food and Drug Administration-reviewed form of selenium-enriched yeast.

BIOPLEX and SEL-PLEX supplementation, either separately or combined with other feed technologies, have demonstrated many immune and growth benefits to a variety of aquatic species in field trials around the world.

In pacific white shrimp, Reyes et al. found that BIOPLEX supplementation increased total hemocytes, plasma protein, phenoloxidase enzyme levels and tissue mineral concentration. Positive trends towards copper were observed in tissue, as well as improved FCR and average shrimp weight.

Sea bream supplemented with 100 mg/kg BIOPLEX Iron achieved the highest antibacterial activity in serum and respiratory burst activity compared to 200 mg/kg of inorganic iron sulfate over 12 weeks (Rigos et al., 2010).  Russian sturgeon fed technologies incorporating BIOPLEX and SEL-PLEX demonstrated a slight reversal in the effects of temperature-induced stress on immunity (Castellano et al., 2017).

Trials have also shown a reduction in fish morality rate when BIOPLEX and SEL-PLEX were provided.  Atlantic salmon smolts receiving 150 ppm of BIOPLEX Zinc showed a 33.4% reduction in mortality compared to the control group (Gatica, Chile). Red hybrid tilapia that were fed Aquate Defender™, a feed technology that incorporates BIOPLEX and SEL-PLEX, showed reduced morality, improved growth and improved feed utilization after being exposed to S. agalactiae and A. hydrophilla (Arifin et al., Malaysia) (Figure 2).

Figure 2: Effect of an Alltech feed technology that incorporates BIOPLEX and SEL-PLEX on the survivability of red hybrid tilapia after an immune challenge (Arifin et al.)

In rainbow trout fingerlings receiving BIOPLEX and SEL-PLEX at 66% of the level of the inorganic trace mineral group, FCR, weight gain, mortality and immunity (via lysozyme activity) were all improved (Staykov, 2005).

Growth and efficiency

When post smolt Atlantic salmon were reared in conditions with suboptimal oxygen, supplementation of BIOPLEX Zinc and SEL-PLEX selenium-enriched yeast improved FCR and growth rate compared to those supplemented with inorganic trace minerals (Figure 3). By the end of the trial, salmon from this group also exhibited firmer filets (Kousoulaki et al., 2016).

Figure 3: Effect of trace mineral source (inorganic vs. organic) and level (commercial levels vs. 2/3 commercial levels) on final body weight and FCR in Atlantic salmon reared in low oxygen conditions (Kousoulaki et al., 2016).

IM; inorganic mineral, OM; organic mineral (BIOPLEX and SEL-PLEX)  

Rainbow trout supplemented with BIOPLEX trace minerals as low as 50% of NRC recommendations were able to maintain optimal performance. When supplemented at 75% of NRC recommendations, performance was significantly improved compared to those fed higher levels of inorganic trace minerals (Filer et al., USA).

When combined with other feed technologies such as proprietary nucleotides, Amazonian pirarucu given BIOPLEX and SEL-PLEX had improved FCR and weight gain compared to the inorganic mineral group. FCR in the organic versus inorganic group was 1.1 versus 1.5, while weight gain in the organic group was 1.5 kg heavier compared to the inorganic group (Silva et al., 2010).

Yellowtail fingerlings fed lower levels of fish meal and lower levels of BIOPLEX and SEL-PLEX showed improved weight gain, FCR and final weights (Fukada and Kitagima). The authors concluded that lower levels of dietary organic trace minerals improved performance, and these levels could also reduce the amount of trace mineral excreted into the environment, contributing to more sustainable aquaculture production.

In summary, research shows that when substituting inorganic trace minerals for BIOPLEX and SEL-PLEX, it can often be done at lower inclusion rates without compromising performance. Lower dietary trace minerals in an organic form can also reduce environmental mineral output, therefore contributing to sustainable aquaculture production systems.

Appropriate mineral management is key to optimum health and performance across several aquatic species, and the incorporation of an organic trace mineral program can have an important role in maximizing fish production and profitability.

References to this article are available upon request. If you have any questions, please contact the Alltech Mineral Management team at KnowYourMinerals@alltech.com

An article by the Alltech Mineral Management Technical Team