Astaxanthin: five factors influencing fillet colouration
Feed costs represent a significant proportion of total production costs in the farming of salmonids. Therefore, it is important to use feeds which promote the best fillet quality possible. For quality and marketing purposes, diets containing astaxanthin are fed during the grow-out phase when pink flesh is desired.
What is Astaxanthin?
Astaxanthine is a lipophilic pigment which accumulates in oils and fat and which is found naturally in many species, such as lobsters, shrimps and salmonids. Initially, it is synthesized by organisms such as marine phytoplankton or other microorganisms; it then follows a path upwards through the food chain. For instance, wild salmon have pink flesh because they eat crustaceans which contain astaxanthin originating from lower trophic levels. When an intense pink colouration is desired in farmed fish, astaxanthin is added to the diet.
1. Feeding
Feeding period, feed intake and feed conversion ratio (FCR), but also the concentration of astaxanthine in the feed all affect pigmentation of the fillet. We recommend starting an astaxanthin-containing feed at half of the targeted harvest weight. For example, when harvest weight will be 500 grams, start feeding an astaxanthin-containing diet from 250 grams onwards. In addition, keep in mind that salmonids cannot deposit astaxanthin well at an early age. Therefore, the effect of astaxanthin will be expressed more as the fish grows, until the onset of maturation. This advice is based on rainbow trout and brown trout; char species lay down astaxanthin much more slowly, which means astaxanthin should be fed at an earlier stage.
2. Maturation stage
At maturation, astaxanthin is redirected, together with other nutrients, from the meat to the eggs. This gives the meat a pale colour and decreases its firmness. This is a pity, as much of the astaxanthin fed is lost, and it takes substantial time to bring back fillet colour after reproduction. Ideally, fish are harvested before maturation, preventing these changes.
3. Shelf-life of the feed
Astaxanthin is very sensitive to oxidation with other compounds, such as vitamins and minerals, which results in reduced colouration. This process can be accelerated by inappropriate feed storage conditions.
Short storage periods and appropriate storage conditions are vital for the preservation of astaxanthin. Optimal storage conditions are detailed below.
4. Trace minerals
Dietary minerals should be present in a stable form and with a high bioavailability to make sure they are utilized effectively by the fish. In addition, stable mineral forms lower the pro-oxidative effect seen with other compounds, such as astaxanthin and vitamins. This stability and bioavailability, will therefore preserve the nutritional quality of the feed.
5. Genetics
For larger harvest sizes of salmon trout, late-maturing or triploid strains are the best choices, as this lowers the risk of de-colouring of the fillet due to redirection of the astaxanthin from the meat to the eggs.
Feed storage recommendations
Proper storage can significantly influence feed quality, mitigating the deterioration of nutritional value within the shelf-life period. Several actions can be taken to protect your feed and its macronutrients, pigments, vitamins and mineral concentration:
- Keep storage areas dry and cool, with a stable temperature.
- Keep storage areas sheltered to protect the feed from rain, direct sunlight and extreme conditions.
- Prevent vermin/pests on the farm, since they can damage or destroy feed bags.
- Keep some space between the feed and the floor.
- Follow shelf-life recommendations.
What do we offer?
Through research with salmonids at the Alltech Coppens Aqua Centre and on-farm with our customers, we have created nutritional formulas and solutions that will ensure an ideal start on all types of farms. Our formulations and production technologies create astaxanthin-containing solutions with just the right palatability and nutritional profiles, enhancing uptake by the animal and promoting optimal digestion of all vital nutrients.
The Alltech Coppens Grower feeds that contain astaxanthin are Supreme Astax, Royal Star Astax, Royal Fario Astax, and Crystal Astax.