Astaxanthin: An important micro-ingredient in aquaculture feeds

Astaxanthin: An important microingredient in aquaculture feeds

Terry W. Snell, Matthew Carberry, John Carberry, Tim Wilson, Sustainable Aquatics

Based on 20 years’ experience breeding hundreds of marine species in our Sustainable Aquatics hatchery, we conclude that adding di-esterified 3S, 3’S astaxanthin as a feed micro-ingredient makes fish more resistant to disease, eliminates the need for antibiotics in the hatchery, improves fish survival, increases growth rates, boosts reproduction and provides exceptional color.

We have learned how to produce di-esterified 3S, 3’S astaxanthin from Haematococcus pluvialis oil that is highly bioavailable and low cost. Astaxanthin from the green alga H. pluvialis is synthesized at an end of the green phase to prepare for encystment of cells so that they can survive desiccation (Kobayashi et al. 1997). This encystment converts the algal cell into a 60 µm cyst which is indigestible and resistant to UV. The widely used supercritical CO2 astaxanthin extraction process breaks cysts down to 5 µm, but denatures astaxanthin in the process. Astaxanthin is most bioactive and stable if it is esterified and not exposed to high temperatures.

We have patented a low-temperature extraction process to break H. pluvialis biomass into particles less than 100 nanometers. The hydrophobic astaxanthin naturally associates with fatty acids, becomes esterified, and self-assembles first into micelles and then liposomes. This lipid-rich, nano-emulsion allows astaxanthin to transit the digestive tract and bloodstream, increasing its bioavailability from 48-700 times.

Astaxanthin requirements in salmon

A recent demonstration of the value of astaxanthin as a feed additive in aquaculture is illustrated in our work with Atlantic salmon. Sustainable Aquatics has been developing husbandry, water engineering and nutrition protocols for salmon RAS aquaculture. When attempting to improve salmon feeds, it is important to understand the natural diet of all phases of the salmon life cycle.

Salmon juveniles start exogenous feeding after about 420 degree-days in the gravel of river bottoms (redd) where they were originally spawned (Solberg et al. 2014). In contrast, the industry typically starts exogenous feeding at 840-degree days at 6°C. This feeding regime starves the alevins for about 110 days

Figure 1. Atlantic salmon growth from 5 through 25 weeks post-hatch.

Figure 2. Atlantic salmon growth in Sustainable Aquatics RAS system week 25 through week 53 post-hatch.

compared to natural salmon populations. Starvation during this period of growth and development is particularly damaging because salmon grow allometrically (Fukuwaka, 1996). Allometric growth means that different body parts grow and develop at different rates. For example, the eyes, mouth, gills, liver and tail are the first to develop and become fully functional because these structures are essential for life as salmon emerge from the redd, capturing prey and avoiding predators. The rate of allometric development is genetically programmed, but if nutritional requirements for this growth are not adequate, salmon are handicapped for their entire lives. Smoltification is another critical stage in salmon development that is strongly influenced by astaxanthin in the diet. As salmon leave rivers and enter the sea, they begin to consume large amounts of krill and shrimp. These prey are especially rich in astaxanthin which contributes to salmon’s red flesh color, rapid growth rate, strong immune system, and minimizes deformities. If aquaculture diets do not provide adequate quantities of this critical micronutrient during this developmental stage, salmon will not realize their full growth potential, disease resistance, or flesh color.

Salmon trials in RAS systems

If land-based RAS systems are going to be successful in salmon production, diets need to be adjusted to fully supply all nutritional requirements and satisfy the needs of managing high water quality. Sustainable Aquatics uses a patented micronutrient delivery system called Amplifeed Topcoat that contains the right amounts of highly bioavailable astaxanthin and several other important micronutrients like taurine, folate, and selenium. We have demonstrated that commercial salmon diets coated with Amplifeed Topcoat produce

Figure 3. Salmon growth in Sustainable Aquatics RAS system compared to Atlantic Sapphire and Mowi.

Figure 4. Flesh color of a 500 g, 50-week-old Atlantic salmon raised with Amplifeed ™ Topcoat in Sustainable Aquatics’ RAS system.

salmon with high survival, that grows and matures quickly, resists disease without vaccinations, and has few deformities. Salmon produced on such a diet also has strong, attractive color and excellent taste.

Salmon rearing trials conducted in RAS systems at Sustainable Aquatics hatchery have demonstrated these principles. Salmon fed a diet with TopCoat on this schedule, developed from alevins to smolts to healthy adults with virtually no deformities.

Salmon growth followed an exponential model (y = 0.083e0.190x) from week 5 through week 25 post-hatch (Fig. 1), when we culled about 25% of the population (fish less than 10 g). Average fish size at 25 weeks was 14 g. During this phase, fish were maintained at 14°C in 200-liter tubs and fed a diet of 10:1 coated with Amplifeed Topcoat.

In week 25, salmon were transferred to a 12,000liter pool for continued grow-out. Growth continued according to an exponential model (y = 0.988e0.129x) through week 53 when the average salmon in this cohort weighed more than 600 g (Fig. 2). Lower than predicted growth after week 49 was probably due to increased crowding as stocking density approached 50 kg/m3. Based on this model, we predict the harvest of 5 kg of fish at 64 weeks.

Salmon growth rates in Sustainable Aquatics’ RAS system can be compared to published data from industry leaders (Fig. 3). There are many differences in these systems that contribute to their marked difference in performance. Chief among them is Sustainable Aquatics’ 14°C temperature, early exogenous feeding of fry, and the use of Amplifeed Topcoat on the fish feed.

Salmon feeds with Amplifeed Topcoat produce fish with a strikingly deep red color (Fig. 4). Figure 4 illustrates the flesh color of a 500 g, 50-week-old Atlantic salmon reared in Sustainable Aquatics’ RAS system and fed a diet of standard Skretting salmon feed with Amplifeed Topcoat. This color corresponds to a value of 34 on a salmon color chart. Preliminary taste tests with experienced salmon consumers indicate that they found it difficult to distinguish the taste of these salmon from wild caught.

We have made great progress designing diets for rearing salmon in RAS systems and now can produce an excellent quality product, quickly, reliably, and cost-effectively. Diet, however, is not the only variable contributing to this success. Effective management of water quality through innovative engineering has also played a key role, but this is a topic for another story.

References available on request.

More information: Terry W. Snell

Professor Emeritus Georgia Institute of Technology E: terry.snell@biosci.gatech.edu

John Carberry

CEO Sustainable Aquatics/Nutrition E: johnc@mosseycreekenterprises.com