Pond aging: turning back the clock on water quality

Fountain of youth?

Using water to turn back the clock on aging? Sounds great. But is this any more than a myth when it comes to shrimp production? Is it truly possible to reverse pond aging?

Feeding rates are proportionally high at the beginning of a production cycle. However, thanks to low biomass at stocking, feed volume is relatively small. As the days of culture (DOC) pass, more feed volume is applied to the pond to feed the growing shrimp. Resultingly, over time, the pond environment will deteriorate. Increased risk of disease is associated with this environment of poor water and sediment quality.

This situation is considered ‘pond aging’. Pond aging refers to the natural process by which a shrimp pond devolves over time, transitioning through various ecological stages. Consequently, ponds with good water quality could be considered as biologically ‘young’, whereas ponds with poor water quality are biologically ‘old’.

Understanding the dynamics of pond aging

All ponds are different, and all ponds age differently. It is important for producers to understand their pond dynamics to ensure a healthy and steady aging process, for a consistent and predictable harvest.

There are many factors that can influence the pond aging process (Figure 1). Most importantly, nutrient build-up and decomposition of organic materials. Other factors include changes in pond biodiversity (bacterial communities and plankton composition), sedimentation (sludge, run off, dissolved particles) and environmental fluctuations.

Most notably, feed plays a key role in determining the rate of pond aging, specifically feed composition – raw materials and digestibility, as well as feed consumption - uneaten feed.

As well as playing a pivotal role in pond aging, feed can also account for up to 80% of the total environmental footprint of a shrimp farm, so a closer look at optimization is essential.

Three management tools are the secret to slowing down pond aging

It goes without saying that management is of upmost importance in pond aging. While it is difficult to reverse pond aging during the cycle, with proper management it is possible to control (and reduce) the rate at which ponds age (Figure 2).

Specifically, pond aging is managed by controlling nutrient inputs, choosing highly digestible feeds and increasing decomposition efficiency.

Selecting the optimum feed

Protein content is often considered an indicator of good feed quality. Did you know that too much protein, or undigestible protein, can increase the nitrogen and phosphorous waste in a pond? (Figure 3).

Both nitrogen and phosphorous are key drivers of pond aging, and from a sustainability perspective, important indicators of biological change.

High protein feed can also affect phytoplankton profiles, stimulating the growth of harmful algae, such as dinoflagellates and cyanobacteria - which can negatively affect shrimp health.

Optimizing feed efficiency with enzyme additives

How do shrimp producers counter this challenge? Feed enzymes are an effective way to improve feed utilization. Under experimental conditions, the positive impact of both protease and phytase enzymes (standalone and in combination) was demonstrated by reducing nitrogen and phosphorous loading, against control by up to ~20% and ~32% respectively (Figure 4).

These reductions can have a big impact in slowing the pond aging process (Figure 5).

Strategic use of bioremediation probiotics

Probiotics are a standard operating procedure in aquaculture pond management. Bioremediation probiotics can reduce nitrogen waste (ammonia, nitrite & nitrate), break down organic matter, control pathogens and positively influence plankton profiles – all key indicators of pond aging.

However, with many formulations on the market it is no surprise that not all are the same, so strategic choices and applications are needed, such as:

• Formulation: single vs multi species
• Application: direct or pre-fermentation
• Credibility: quality control, trial data

A recent field trial in Indonesia demonstrated the benefit of a multi-genera probiotic, AquaStar® applied directly to the pond, versus a protocol which involved a pre-fermentation step. From observation alone, it was clear that the direct application of AquaStar® is more efficacious - shown by water coloration and biosurfactant (which shows the strains viability) (Figure 6).

What’s next?

Pond aging is an inescapable natural process in the aquaculture ecosystem. Understanding the dynamics involved in pond aging is essential to implement appropriate, robust management practices. Feed and water-based solutions, such as enzymes and bioremediation probiotics are complementary to support reducing phosphorous and nitrogen effluents - whilst having a positive influence on bacterial and plankton communities.

Using these tools to slow pond aging helps to maintain pond health and productivity in the long run. The result is minimal pond down time, increased profitability, both of which are the foundations of more sustainable aquaculture.