Choosing the Right Shrimp PL: Genetics, Health and Quality Before Stocking

By Dr. Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Sun Sep 20 2026

Choosing a good PL is one of the most important decisions for successful crop. Once PL are stocked into the pond, farmers have already committed feed, electricity, labour, pond preparation and several months of production time.

L. vannamei PL under microscopePhoto credit: Doctor Shrimp AI-Powered Care, India

Today, L. vannamei PL are available from different genetic programmes. Most commercial genetics can broadly be grouped into three strategies: fast-growing, robust and balanced lines.

1. Fast-Growing Genetic Lines

Fast-growing lines are selected mainly for rapid weight gain and shorter culture periods. These PL are most suitable for farms with good biosecurity, stable water quality, strong aeration, good feeding management and relatively low disease pressure. Commercial performance data from one fast-growth programme report average daily growth of approximately 0.35–0.42 g/day under suitable intensive farming conditions. At an ADG of 0.35 g/day, for example, shrimp could theoretically add about 10.5 g of body weight in 30 days during a strong growth phase. However, fast growth requires the pond environment to support that genetic potential. If DO, water quality, disease pressure or feeding management become unstable, the expected growth advantage may not be fully expressed

2. Robust Genetic Lines

Robust lines are selected with greater emphasis on survival, environmental tolerance and performance under disease pressure. These lines may be more suitable for earthen ponds, farms with recurring disease challenges or environments where temperature, salinity and water quality fluctuate. Published commercial technical information from a robustness-selected line reports approximately 0.21–0.28 g/day ADG, corresponding to around 21–28 g ABW after approximately 100 days under suitable culture conditions. The goal of a robust line is not necessarily to achieve the highest possible growth rate. Its value is maintaining acceptable growth while improving the probability of survival when environmental or disease pressure increases.

Photo credit: Blue Aqua Breeding Center, Singapore

3. Balanced Genetic Lines

Balanced lines are selected for several traits at the same time, typically: growth + survival + feed efficiency + disease tolerance + environmental adaptability. Rather than pushing one trait to the maximum, the objective is stable performance across different farming conditions. Commercial pond data from a balanced genetic programme covering 98 ponds reported:

ADG around 0.20–0.22 g/day, Survival around 79–86%, FCR around 1.19–1.33 across low, medium and high salinity environments. These numbers should not be used to directly rank one genetic type against another because stocking density, feed, salinity, pond management, disease pressure and harvest age were different.

The important message is that genetics should be selected according to the farm environment, not simply according to which PL is advertised as growing fastest.

Check PL Before Stocking Is Mandatory

Photo credit: Doctor Shrimp AI-Powered Care, India

Step 1: PCR Checking for Disease

PL can look healthy while still carrying pathogens. PCR detects the genetic material of specific pathogens in the PL. Depending on the disease, it can identify viral DNA or RNA, bacterial virulence genes or DNA from microsporidian parasites such as EHP. For shrimp PL, an appropriate screening panel can include WSSV, IMNV, IHHNV, TSV, EHP, AHPND, and Vibrio parahaemolyticus.

“How does disease reach the PL?

Some shrimp viruses can be transmitted from infected broodstock to offspring through reproductive tissues, eggs or contamination associated with spawning. Vertical transmission is particularly important when considering pathogens such as IHHNV and WSSV. But EHP behaves differently. EHP is not generally considered a true ovarian or transovarial infection. Instead, its spores can spread through contaminated water, faeces, equipment, tank surfaces and infected animals. PL can therefore become infected during hatchery production even when transmission did not occur directly through the ovary. AHPND-associated Vibrio, other Vibrio infections and many bacterial problems are also mainly acquired horizontally from the environment.”

Sample Size Matters for PCR

PCR results are only as representative as the sample submitted. Testing a very small number of PL may miss an infection when pathogen prevalence is low. For batch-level evaluation, collecting at least around 200 PLs for PL > 10 (300 PLs for PL < 10) from different parts of the population provides a more representative sample than testing only a few animals.

Step 2: Physical Quality Examination

After disease screening, PL should be examined physically under microscope. Each parameter tells us something different about PL development.

PL stage: Confirm that the declared PL age matches its actual development.
Body-to-gut ratio: A good-quality PL should have an approximate body length-to-gut length ratio of 4:1.
Rostral spines: Rostral development helps verify whether the claimed PL stage matches the actual biological stage.
Gut fullness: The gut should be well developed and visible through much of the body. A continuous, well-filled digestive tract suggests active feeding and good nutritional condition.
Size variation: PL within the same batch should be reasonably uniform.
Gill development: Good gill development is important for respiration and osmoregulation, particularly during salinity changes.

Necrosis: Check the body and appendages for blackened, damaged or necrotic tissue. Necrosis can indicate injury, bacterial problems or environmental stress.
Parasite Infection: Check the gills, appendages and exoskeleton for attached organisms or heavy fouling. High ectoparasite levels usually indicate poor water or tank hygiene.
Structural deformity: The rostrum, antennae, abdomen, tail fan and appendages should be properly formed. Bent bodies or abnormal appendages can indicate developmental stress.
Hepatopancreas: The HP should appear well developed and have a healthy appearance (a lot of fat droplets).

Step 3: Survival Test

Salinity stress test: The test helps assess the ability of the PL to handle osmotic stress, which is especially important before transport and stocking into ponds where salinity may differ from hatchery water.
Formalin stresstest: PL are exposed to a controlled formalin concentration for a defined period and then evaluated for survival and activity. This provides another measure of general hardiness.

PL Passport: Turn PL Testing Into a Stocking Decision

Farmers today receive a large amount of information about genetic lines, hatcheries and PL performance. The difficult question is: Should I stock this particular batch?

This is the purpose of the PL Passport Package from Doctor Shrimp Health Center, powered by AI and operated by Blue Aqua.

PL Passport evaluates PL through three important layers:

PCR Disease Screening

Physical Quality Examination

Survival Testing

The information is then evaluated together to provide farmers with a clearer picture of the PL batch before stocking. PL Passport does not replace the farmer's decision and does not guarantee crop success. It provides something more practical, evidence before the decision is made. Because choosing genetics tells you what the shrimp could become. Checking the PL tells you what you are actually putting into your pond.

Good genetics gives potential.

Good PL gives a strong start.

Testing protects the decision.