The oft-overlooked water quality parameter: pH

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The oft-overlooked water quality parameter: pH

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Farmers are aware of the importance of monitoring levels of dissolved oxygen in their production systems and of providing supplemental aeration in intensive fish and shrimp ponds. However, other water quality parameters – as simple as they may look – are often overlooked. One such parameter is pH, which in chemistry refers to a numeric scale used to specify the acid or alkaline condition of an aqueous solutions.

In a practical sense, water pH may range from 0 to 14 and is related to the concentration of hydrogen ion (a strong acid) in pond water. Pond water may be acid (pH < 7.0), neutral (pH= 7.0) or alkaline (pH > 7.0). In general, farmed fish and shrimp exhibit better production performance and health at water pH values ranging from 7.5 to 8.5, as these values match the pH of their blood and hemolymph (Fig. 1).

Fig. 1: Guidance for pH monitoring for cultured freshwater fish and marine shrimp. The “Warning” ranges indicate potential harmful effects on growth, FCR, immunity and survival of the cultured animals. Aquafarmers should routinely monitor water pH in their production ponds.

Nonetheless, as with dissolved oxygen, water pH values can experience wide fluctuations during the day in green water ponds (Fig. 2). Values of pH near or above 9.0 are quite common during afternoon hours, due to the intense photosynthesis activity by microalgae (phytoplankton), even in ponds with well buffered waters (i.e., waters that are rich in carbonates and bicarbonates and, thus, of high total alkalinity titration and capable of maintaining more stable pH values). Extreme pH, by itself, depresses feeding activity, reduces growth, negatively affects FCR and suppresses the immune response of cultured fish and shrimp.

Fig. 2. Illustration of pH variation during the day according to the abundance of phytoplankton in pond water. Phytoplankton abundance can be indirectly assessed by using Secchi Disk visibility. The more abundant the microalgae population is, the wider the pH fluctuation can be expected during the day.

See more at: https://www.aquaculturealliance.org/advocate/the-oft-overlooked-water-quality-parameter-ph/

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