Traditionally , the nutrients present in Artemia cysts (protein, fat, minerals, etc.) are provided to young shrimp larvae by the use of recently hatched living Artemia nauplii. This involves a time consuming operation: decapsulation; disinfection; hatching; separation and rinsing. Hatching typically takes 24 hours, requires the use of chemicals and is not totally efficient, since the hatching percentage is variable. But recent research has shown that this is not necessary the only way Artemia cysts can be fed. It is well known that Artemia cysts contain an embryo whose development has been arrested at gastrula stage (Clegg et al., 1996). This embryo is composed of a small number of cells and is surrounded by a huge number of very tiny packed granules of nutrient reserves called yolk platelets (Clegg, 2005). Yolk platelets are very regular, well defined bodies measuring 3 £gm in width x 5 £gm in length and present a disk like structure at both ends (Figure 1). These yolk platelets are extremely stable in water and contain virtually all the nutrients needed by the Artemia embryo to continue its development (Figure 2). When properly extracted and processed into the right particle size, these yolk platelets show nutritional properties similar or better than the live Artemia nauplii, when fed to shrimp larvae under commercial hatcheries conditions. The conditions of pH and temperature are key to preserving the integrity of the yolk platelets.

Yolk platelets are the most perfect micro-capsules that nature has produced - or man has invented. It is extremely stable in the slightly acid pH (<6.5) found in diets and spontaneously dissolves at alkaline pH prevailing in the shrimp larval gut (8.5) (Utterback and Hand, 1987). Yolk platelets are therefore the ideal nutrient supply to the young shrimp larvae since its digestion does not rely uniquely on shrimp larval enzymes, but is endogenous to the yolk platelet. Several experiments carried out in hatcheries have shown that Litopenaeus vannamei shrimp larvae fed with yolk platelets particles, replacing fully the use of live Artemia nauplii, grow better and survive better than the shrimp larvae fed with live Artemia nauplii. The water quality of culture tanks and the bacteria load of the water remained similar in both treatments.

Table 2 presents the detailled results of the experiment carried in Mexico in August 2009. Results indicate that Vitellus has produced shrimp post larvae of equal size and quality (CV, Stress test survival and pigmentation) as compared to live Artemia nauplii. The variability of the results in all tanks was well in line with the average of the hatchery.

These pictures show the digestive track of PL3 sampled to evaluate their feeding behavior. Feed can be found in animals from both treatments. The coloration found in the shrimp digestive track fed with Vitellus is more intense probably because the shrimp has ingested more feed.

References:

James S. Clegg (2005): Desiccation Tolerance in Encysted Embryos of the Animal Extremophile, Artemia. INTEGR. COMP. BIOL., 45:715–724 (2005)

Paul J. Utterback and Steven C. Hand (1987): Yolk platelet degradation in preemergence Artemia embryos: response to protons in vivo and in vitro. Am J Physiol 1987, 252:R774-R781.

James S. Clegg, Laurie E. Drinkwater and Patrick Sorgeloos (1996): The metabolic status of Siapause Embryos of Artemia fransciscana (SFB). Physiological Zoology 69(1): 49-66.

This article is reproduced with permission from the Aquafeed.com magazine: Autumn 2010 issue of AQUAFEED - Advances in Processing & Formulation