The focus is on the advantages of a micro-encapsulated diet – from ensuring biosecurity during hatchery operations to its economics
By Mark Rowel Napulan, Peter Van Wyk and Ramir Lee
Artemia nauplii have been a critical live diet for penaeid shrimp larvae in commercial marine shrimp hatcheries since the 1960s (Cook and Murphy, 1966). They are rich in essential fatty acids, proteins, and other nutrients required by shrimp larvae for optimal growth and development. Artemia nauplii have several attributes that have contributed to their widespread use in commercial shrimp hatcheries. The size of Artemia nauplii is highly suitable for shrimp larvae. The cysts can be easily stored with a long shelf-life and can be hatched on demand. Despite all these advantages, Artemia nauplii do not epitomise as a perfect feed.
Issues with Artemia nauplii
The nutritional value of Artemia nauplii can be highly variable. It is at its maximum immediately after hatching. The nutritional value of the Instar 1 nauplii declines continuously with time after hatch as the nauplii deplete the nutrients stored in the yolk sac. The nutritional value of Artemia nauplii varies considerably between different geographic strains and from one year to the next.
A common practice in commercial shrimp hatcheries is to parboil and then freeze Artemia nauplii prior to feeding. Feeding frozen nauplii makes it easier for shrimp larvae to capture them, reducing the risk of overfeeding and preventing tanks from becoming over-populated with adult Artemia. However, the process of parboiling and freezing nauplii leads to the degradation of some proteins and further loss of nutritional value.
The biggest weakness associated with the use of Artemia nauplii in hatcheries is that they present a major biosecurity risk. Hatched nauplii are an important vector for the introduction of Vibrio into larval rearing tanks (Lavilla-Pitogo et al., 1990; Lopez-Torres et al., 2001). Glycerol released by the cysts during the hatching process provides an ideal culture medium for Vibrio (Van Stappen et al., 2024). As a result, Vibrio loads in both the hatching water and in the nauplii themselves can be extraordinarily high (Table 1). Decapsulation of the cysts prior to hatching reduces Vibrio loads, but only slightly. Disinfection of hatched nauplii prior to feeding reduces Vibrio counts but is not 100% effective.
| Vibrio counts | |||
| Capsulated cysts | De-capsulated cysts | ||
| Water (x 106 CFU/mL) | Artemia (x 109 CFU/mL) | Water (x 106 CFU/mL) | Artemia (x 109 CFU/mL) |
| 6.20 ± 0.45 | 1.20 ± 0.90 | 2.00 ± 1.50 | 0.45 ± 0.24 |
Table 1. Vibrio counts isolated from Artemia hatching water and Artemia nauplii from hatching tanks stocked with non-decapsulated and de-capsulated cysts (Interaminense et al., 2014).
Figure 1. Results of challenge trials where the survival of juvenile shrimp fed with feed top coated with Rescue is compared with survival of shrimp fed with feed without Rescue. The graph on the left shows results when challenged with Vibrio harveyii, while the graph on the right shows results when challenged with Vibrio parahaemolyticus.
Replacing Artemia with a liquid micro-encapsulated diet
In 1997, Zeigler developed a biosecure liquid micro-encapsulated diet called EZ Artemia to replace live Artemia nauplii. This diet was formulated with marine protein and lipid sources to exceed the nutritional value of enriched Artemia nauplii. The marine protein sources are PCR-tested to guarantee the final product is free from Vibrio and all World Organisation for Animal Health (WOAH)-listed shrimp pathogens. In addition, this diet contains Vpak, a blend of ingredients promoting improved larval immune function.
In 2021, EZ Artemia Ultra was launched after nearly 25 years of continuous R&D. Compared to the original EZ Artemia, this product has a higher nutrient density and improved ingredient digestibility. The microcapsules are almost neutrally buoyant and will remain suspended in the water column nearly indefinitely with minimal aeration. The microcapsules contain 1.0 x 107 CFU/g of Rescue, a proprietary blend of four species of Bacillus bacteria selected for their ability to control the most pathogenic species of Vibrio. The liquid fraction of EZ Artemia Ultra contains 1.0 x 107 CFU/g of Remediate, a blend of Bacillus species selected for their ability to digest organic matter and control ammonia.
In studies conducted at the University of the Philippines Visayas, it was demonstrated that Rescue administered in the feed effectively colonised the gut and provided significant improvement in challenge trials with Vibrio parahaemolyticus and Vibrio harveyii (Figure 1).
Commercial trials
Trials conducted at Zeigler’s Aquaculture Research Center (Z-ARC) showed that EZ Artemia Ultra can replace 100% of the nauplii in the larval rearing protocol. Nevertheless, most hatcheries prefer to use the liquid microencapsulated diet to replace 30-50% of the nauplii in the diet. When the diet is used to partially replace Artemia nauplii, many hatcheries reported higher survival rates as compared to when no nauplii were replaced.
In recent trials at an Indonesian hatchery (Figure 2), replacement of 100% of the Artemia nauplii in the diet between zoea 3 (Z3) and post larva 1 (PL1) resulted in survival increasing by 32% . In the second trial at the same hatchery, replacement of 33% of the nauplii fed from PL1 to PL8 improved survival by 33% compared to a control group. In both trials, the final weights of the post larvae harvested were the same for both treatment groups.
Economics of Artemia replacement
Replacing Artemia nauplii in the feeding protocol can potentially reduce production costs. When costs are compared based on equivalent usage rates, the liquid microencapsulated diet is likely to be cheaper than using Artemia nauplii, whether hatched from cysts or purchased pre-hatched as an Artemia nauplii paste (Table 2). Additional costs associated with hatching Artemia cysts should be considered.
Figure 2. Comparison of survival rates in tanks fed with EZ Artemia Ultra replacing a percentage of the Artemia nauplii in the feed protocol. The graph on the left shows the results of a trial in which 100% of the Artemia nauplii were replaced with EZ Artemia Ultra from Z3 – PL1, while the graph on the right shows the results of a trial in which 33% of the Artemia nauplii were replaced with EZ Artemia Ultra from PL1 – PL8.
However, when comparing the economics associated with the use of Artemia nauplii with the use of EZ Artemia Ultra, one must also consider how differences in survival affect hatchery profitability. If improvements in biosecurity and reduced viral loading result in higher survival rates, revenues from the sale of post larvae will increase. The impact of higher survival on revenues will often have a much larger impact on hatchery profitability than the impact of the price differences for different feeding protocols.
| Product | USD/kg | Kg required to equal 100 million Artemia nauplii | Cost/100 million Artemia nauplii equivalent (USD)* |
| EZ Artemia Ultra | 57.00 | 0.76 | 43.26 |
| Artemia cysts* | 95.00 | 0.48 | 45.67 |
| Artemia nauplii paste | 40.75 | 1.23 | 50.31 |
| *Note: The price of Artemia cysts can vary widely based on quality, origin, and annual supply. | |||
Table 2. Cost per kg of EZ Artemia Ultra, Artemia cysts, and Artemia nauplii paste expressed as cost per 100 million Artemia nauplii equivalent amount.
Artemia nauplii have been demonstrated to be a major vector for the introduction of pathogenic Vibrio into larval rearing tanks which causes severe diseases such as acute hepatopancreatic necrosis disease (AHPND) and transparent post larva disease (TPD). These diseases can lead to high mortality rates in hatcheries, significantly impacting hatchery productivity and profitability. When Vibrio infected shrimp are introduced to farms the bacteria can result in outbreaks and major losses for the farms. EZ Artemia Ultra is a biosecure larval diet that can help reduce bacterial loads in larval shrimp tanks and support higher survival rates. This diet is an economical and convenient biosecure alternative to Artemia nauplii.
References
Cook, H. L. and Murphy, M. A. 1966. Rearing penaeid shrimp from eggs to postlarvae. Proceedings 19th Annual Conference Southeastern Association Game and Fish Commissioners 19: 283–288.
Interaminense, J.A., Ferreira Calazans, N., do Valle, B.C., Lyra Vogeley, J., Peixoto, S., Soares, R. and Lima Filho, J.V. 2014, Vibrio spp. Control at Brine Shrimp, Artemia, Hatching and Enrichment. J World Aquacult Soc, 45: 65-74. https://doi.org/10.1111/ jwas.12096
Lavilla-Pitogo, C. R., Baticados, M. C. L., Cruz-Lacierda, E. R. and De la Peña, L.D. 1990. “Occurrence of Vibrio species, including Vibrio harveyi, in Penaeus monodon hatcheries in the Philippines.” Aquaculture, 91(1), 1-13.
Lopez-Torres, M. A. and. Lizarraga-Partida, M. L. (2001). Bacteria isolated on TCBS media associated with hatched Artemia cysts of commercial brands. Aquaculture 194:11–20.
Van Stappen, G., Sorgeloos, P. and Rombaut, G. (eds.) (2024). Manual on Artemia production and use. FAO Fisheries and Aquaculture Technical Papers, No. 702. Rome, FAO. https://doi. org/10.4060/cd0313en