How shrimp are distributed within the pond and why this alters both your sampling and feeding strategies

It is six in the morning at a shrimp farm in the Gulf of Guayaquil. Rowing slowly across the pond, a technician casts a cast net over the same spot as always—near the feeding areas where “everyone knows” shrimp congregate—and pulls up a full pocket. He records the weight, estimates the total pond biomass based on that handful of animals, and uses this figure to determine the feed ration for the coming days. This is the routine at thousands of shrimp farms across Ecuador and every other producing nation. Yet, according to a new study conducted in 5-hectare commercial ponds, this routine may be yielding highly inaccurate figures.

Because shrimp do not distribute evenly within a pond. Instead, they concentrate in specific zones and consistently avoid others; ignoring this spatial behavior distorts every subsequent management decision: population sampling, feed rationing, aerator placement, and even where to focus monitoring when water quality begins to deteriorate.

Key Findings of the Study

• Aggregated Distribution: Juvenile shrimp exhibit a clustered or aggregated distribution rather than random dispersal across the pond, forming schools and occupying specific zones more heavily throughout the culture cycle.
• The “Borrow Pit” Avoidance: The “borrow pit”—the deeper channel along the pond dikes—harbors the lowest concentration of shrimp, with significantly fewer animals captured there compared to the flat bottom (“mesa”) or the feeding zones.
• Depth as a Predictor: Water depth is the strongest predictor of shrimp spatial distribution, showing an inverse relationship: the deeper the water, the lower the shrimp density.
• Size Segregation on the “Mesa”: The largest shrimp were caught on the “mesa” (the vast, flat central area of the pond), where the average body weight was significantly higher than in the borrow pit.
• Sampling Bias: Sampling consistently in the same locations heavily biases biomass estimation; understanding the actual spatial mapping of shrimp is key to optimizing sampling, feeding, and aeration strategies.

A problem as old as earthen ponds

Anyone managing an earthen shrimp pond in Ecuador is familiar with its anatomy. There is the “mesa” (the broad, flat surface spanning most of the pond area), the feeding zones where feed is distributed or automatic feeders are installed, and the “cuneta” or borrow pit—the deep perimeter trench resulting from excavating soil to build the dikes, where organic sludge naturally accumulates due to water dynamics.

For years, it was assumed that shrimp roam everywhere and crowd around feeders during feeding times, a premise that determined where to sample, place aerators, and calculate feed rations; yet, almost no one had measured if shrimp actually behave this way in commercial-scale ponds rather than laboratory tanks. This is where this study comes in, as a team from the Technical University of Machala (UTMACH) and the Federal University of Santa Catarina in Brazil monitored Kishor S.A. shrimp farm in Isla Inglesa for 50 days to answer two simple yet critical questions: do shrimp disperse randomly or form aggregates, and which pond parameters dictate where they settle?

How they found out: Cast nets, stakes, and patience

The methodology was as artisanal as it was rigorous: selecting three neighboring ponds (4.9, 5.2, and 5.5 hectares) and dividing each into 24 quadrants marked with wooden stakes. A cast net was thrown at the center of each quadrant—away from feed trays to avoid biased counts—to count, weigh, and release every shrimp.

This exercise was repeated three times during the production cycle at three target sizes: small (6.86 g), medium (13.47 g), and large (20.94 g), while concurrently measuring temperature, dissolved oxygen, pH, salinity, Secchi disk visibility, light intensity, and depth at all 24 points (yielding 216 net casts per pond). To analyze spatial clustering, they applied the dispersion index: a value of 1 indicates random distribution, less than 1 denotes uniform spacing, and greater than 1 signifies aggregated clustering, with the index consistently exceeding 1 across all trials.

What they found: Shrimp school together and avoid deep areas

The first major finding is that shrimp consistently aggregate across all sizes, zones, and ponds. Rather than dispersing, they exhibit schooling behavior and move as a cohesive group—a trait documented in other penaeids and confirmed here under real commercial farming conditions, suggesting it is an inherent behavioral trait rather than a temporary environmental reaction.

The second finding directly impacts your bottom line: the deep borrow pit harbors significantly lower shrimp density. While densities hovered around 6.3–6.5 shrimp per square meter on the flat “mesa” and feeding zones, they dropped to nearly 5 in the borrow pit, with depth emerging as the strongest predictor (a clear inverse relationship: every additional centimeter of depth led to lower shrimp abundance).

Why? Although the study did not measure sediment directly, it points to a well-known phenomenon: deep areas accumulate organic matter and develop less favorable conditions, such as benthic oxygen depletion and the accumulation of toxic metabolites like ammonia and hydrogen sulfide, which shrimp actively avoid.

Beyond depth, temperature and individual weight also played significant roles with direct relationships; warmer water hosted higher shrimp concentrations, which is expected for cold-blooded animals whose metabolism and activity are temperature-dependent. Interestingly, even small temperature variations within commercial ponds moved the needle, despite being below ideal laboratory-reported feeding ranges, while variables like dissolved oxygen, pH, and light showed no clear effect—likely due to active aeration maintaining uniform oxygen levels and high water turbidity diminishing the role of sunlight on these bottom-dwelling animals.

The “Mesa”: Where the Big Ones Grow

There is a crucial detail no producer should overlook: the flat “mesa” does not just host more shrimp—it hosts the largest ones. The average weight of the animals caught there was significantly higher than that of those in the borrow pit. The “mesa” behaved as a stable, homogeneous environment, likely with more natural food available and better overall conditions, making it the preferred “residential neighborhood” for larger individuals.

The feeding zone occupied a middle ground and, surprisingly, showed more variable occupancy. In other words, while commercial feed is a key resource, it is not the sole factor determining shrimp distribution. The animals move between zones seeking food, environmental stability, and physiological safety concurrently, rather than remaining glued to the feeders as is often assumed.

Practical Implications for Your Shrimp Farm

This is where science turns into practice. If shrimp avoid deep areas and concentrate on the flat bottom, sampling consistently in the same spot—or worse, right next to the feeders—provides a highly skewed snapshot of your biomass, which is the very metric used to calculate feed rations. A stratified sampling protocol covering all three functional zones yields a far more representative figure.

The same logic applies to feeder and aerator placement: positioning them where the animals actually reside, rather than where we assume they are, maximizes the efficiency of every bag of feed and every hour of motor operation. Furthermore, since the deep borrow pit has both the lowest shrimp density and the highest susceptibility to degradation due to sludge accumulation, it is precisely the area that warrants the closest environmental monitoring throughout the cycle.

A point of honest clarification is warranted, as noted by the authors: while the tendency to aggregate was clear, they did not detect a statistically stable, perfect aggregation pattern across every single observation. Science rarely provides absolute certainty; it offers well-founded directions. And the direction of this study is crystal clear: depth dictates distribution, the borrow pit repels, and the “mesa” hosts the giants.

Back to the Canoe

Let us return to the technician at six in the morning. If, instead of repeatedly casting his net in the same spot near the feeder, he distributed his casts across the “mesa,” the feeding area, and the borrow pit, he would obtain a biomass estimate that truly reflects what is swimming beneath the surface. He would adjust rations based on data, not assumptions. He would inspect the deep trench not because shrimp are there, but precisely because they are not—which, in an earthen pond, is often the first warning sign of benthic deterioration. The shrimp, it turns out, have been telling us where they live all along. We just needed to cast our nets a little wider to listen.

Contact
Marco Shizuo Owatari
Laboratory of Algae Cultivation, Aquaculture Department, Federal University of Santa Catarina
Florianópolis, Brazil
Email: marco.owatari@ufsc.br

Reference
Blacio, W. A. M., Agila, E. D. A., Owatari, M. S., & Arana, L. A. V. (2026). Spatial distribution of juvenile Penaeus vannamei cultivated in earthen ponds: Effect of functional zoning and water quality parameters. Aquacultural Engineering, 115, 102783. https://doi.org/10.1016/j.aquaeng.2026.102783

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.