Post-larval growth and quality are crucial for the long-term success of China’s shrimp hatcheries and the entire shrimp farming industry. Optimizing these critical parameters hinges on the significance of larval and post-larval nutrition. Premium nutrition during the early-life stages ensures synchronized molting, post-larval growth, enhances disease resistance, and stabilizes production. An INVE Aquaculture field trial in a prominent hatchery in the Hainan region demonstrated how using quality products can boost post-larval quality without incurring extra costs for the hatchery.
Importance of larval nutrition for post-larval performance
The zoea stage is a critical juncture in a shrimp’s life cycle as the nauplius shifts from relying on internal energy reserves to becoming an actively feeding organism (Figure 1). Adequate nutrition from this stage is crucial for developing robust and healthy post-larvae. Proper nutrition tailored to each development stage is vital for synchronized molting, ensuring a successful transition to the post-larval stage. Furthermore, early PL stages benefit from diets containing highly digestible protein sources, helping mitigate an enzyme crisis around PL3.
|Figure 1: Healthy zoea individual (stage 1)
The practice and pitfalls of cocktail feeding
In China, the color of a young post-larvae’s hepatopancreas (PL) often determines its quality, with a black color preferred as a sign of good performance. To balance quality and cost-efficiency, many Chinese hatcheries create their own feed cocktails, often using a mix of low-cost local brands upgraded with additives.
We advocate using qualified diets and probiotics for several reasons:
- Complete and consistent nutrition: Quality diets provide balanced feed with high digestibility, including marine protein sources, vitamins, minerals, amino acids, and astaxanthin. Preparing feed cocktails can lead to mistakes.
- Homogeneous feed particles: Ensuring uniform feeding for all larvae promotes synchronized molting.
- Feed particles of adequate size: Reduces feed waste, organic matter levels, and the risk of Vibriosis.
- Micro-encapsulation technology: Micro-encapsulated diets efficiently deliver nutrients to larvae and prevent leaching into the water, reducing Vibrio growth.
- Easier traceability: Using fewer products simplifies warehouse management and traceability.
Furthermore, the application of high-quality products should align with the specific needs of each hatchery, following a tailor-made protocol known as ‘Best Balance’ by INVE Aquaculture, which was implemented in a prominent L. vannamei hatchery in Hainan.
Set-up of the trial
INVE’s Best Balance protocol was executed in 5 replicate tanks and compared with the hatchery’s standard protocol in 5 replicate tanks. Each tank was stocked with 3.8 million nauplii in 9 MT water and reached a final volume of 18 MT water at harvest. The objectives were to compare production parameters, survival, growth, post-larval quality, and evaluate protocol cost.
Cocktail feeding versus “Best Balance”
The hatchery’s approach to shrimp nutrition was to mix diets from several producers and further ‘upgrade’ them by adding black flakes, minerals, enzymes, vitamins, and other additives. INVE’s Best Balance protocol proposal included micro-encapsulated diets FRiPPAK® FRESH #1 CAR designed as a partial algae replacement for zoea stages, and FRiPPAK® FRESH #2 CD to meet the nutritional needs of mysis stages. Lansy-Shrimp ZM was later introduced to the protocol to answer different market needs.
FRIPPAK® PL+ ULTRA 150 was used to cover the needs of early-stage PL for highly digestible protein sources. Finally, the health booster Sano® S-PAK 0/2 was included to strengthen the PL’s immune system, and Sanolife® MIC, a probiotic mix, was used for optimal vibrio control.
Larvae following the Best Balance protocol molted faster and had better water quality and lower turbidity. In contrast, fouling, necrosis, and Zoothamnium growth were observed in the standard hatchery tanks (Figure 2). Zoothamnium is a genus of ciliate protozoan that typically attaches to plants, animals, or any solid substrate. Although they do not cause histological damage, they can compromise the ability of the gills to pass on oxygen to the other tissues. Post-larvae from the Best Balance tanks did not suffer from these issues and showed higher levels of lipid droplets in their hepatopancreas (Figure 3).
|Figure 2: Appearance of Zoothamnium on the shrimp post-larvae – microscopic observation
|Figure 3: Lipid droplets in the hepatopancreas (dorsal view – PL4)
Evaluation of culture performance and protocol cost
Growth and survival rates were similar between the two protocols. When evaluating protocol cost per million PL5 produced, there was no significant difference (Table 1), indicating that using quality diets from a trusted supplier does not necessarily result in higher protocol costs.
|Table 1: Survival, product, and production cost at the level of the individual tanks. Costs are in Chinese Renminbi (RMB)
Sampling to determine success
An essential aspect of this field study was the method used to assess the post-larvae at PL4-5. The traditional visual assessment method used by Chinese hatcheries for PL quality was enhanced in this study. Microscopic observations provided a holistic understanding of post-larvae’s nutritional status, stress levels, and overall well-being. PL on the INVE diets showed higher lipid droplet counts, even with paler hepatopancreas color, challenging the traditional assessment based solely on hepatopancreas color.
In summary, the field trial demonstrates the significance of high-quality nutrition and tailored protocols for post-larval shrimp, highlighting the potential benefits of a holistic approach to quality assessment.
The use of quality diets and probiotics following the Best Balance approach can leverage post-larval quality in Chinese hatcheries to implement safer, more traceable, and more consistent feeding strategies with:
- PL of higher quality at a similar production cost
- Cleaner, healthier tank water conditions (less pathogens, less organic waste and ammonia)
- Better performance (survival rate) downstream
PL quality assessment based on microscopic inspection of shrimp gills, body, and the hepatopancreas in addition to visual inspection by eye can:
- Give a more complete evaluation of the PL’s health and nutritional state
- Prevent the potential loss/rejection of good PL
Authors: Prateep Saengpeng (K. Den), Chai Yu, Qunxiong Mo, Jiahui Wu, Amir-Antoine Khalil, Andrew Shinn, Ratchakorn Wongwaradechkul, Alfredo Medina, Frederic Jozwiak, and Eva Werbrouck.
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