Aquaculture Water Quality for Small-Scale Producers - Aquaculture and the Environment: A Shared Destiny - page 133

If low air temperatures are presented, covering the tanks with plastic sheets could be is
useful (Van Gorder, 2003; Crab, 2009). On the other hand, if temperature rises, a packed
aeration column can be built as a chiller (Wheaton, 1982). In both cases (low and high water
temperatures), to add new make-up water can be useful. Is also important to remember that
some fish doesn't growth on winter, like tilapia (Crab et al., 2009)
If fish tanks are used, it could be helpful to cover its walls with heat insulators. Elastomeric
foams are a good choice, because they are generally designed to support extreme insulation
and hard management. Fiber glass and polystyrene foams could be used, too (Alatorre, 2010).
Another option is to consider solar heating water systems. Despite the high initial cost, they
can help to raise the water temperature from 1 to 5 °C. Solar pool blankets, geodesic
structures and active/passive solar collectors have been tested with considerable results
(Fuller, 2007). A practical guide and cases studies is available in www.retscreen.net. A
complete guide to thermosolar processes can be found on Duffie and Beckman (1992).
3.2 pH
A common action to pH control is the addition of chemical substances. When pH is low, it
could be useful adding lime (Wurts and Durborow, 1992). If pH rises, small amounts of
phosphoric acid or acetic acid can help to neutralize water. Some people uses sulphuric acid,
but it can be dangerous if there is no previous experience on dangerous substances
management. Another way to pH control is the enrichment of the biological activity in the
pool (Hargreaves, 2006).
In our experience, many traditional aquaculture managers do not monitoring pH. This can
be a bad choice, because as we discussed previously, a certain combination of temperature,
pH and ammonium can kill entire production stocks.
In the case of aquaponics systems, pH management is fundamental. In this kind of systems
plants, fish and bacteria are cultivated. In general, the nitrogen cycle is completed inside the
culture water, and the final metabolite (nitrate) is assimilated by plants. As a result, the
nutrients provided by fish feed are recycled, and the negative environment impacts are
diminished (Diver, 2006). But there is a problem. The optimum pH value for plants, fish and
bacteria is 6, 7 and 8 respectively. There is necessary reconciling pH in this systems. Tyson
(2008a,b) recommended a pH value of 8 to improve nitrogen assimilation by bacteria.
3.3 Dissolved oxygen
Mechanical aeration is by far the most common and effective way to increasing DO
concentrations in ponds. In semi-intensive aquaculture, aeration is applied in case of
emergency.(Boyd, 1998).
Paddlewheel aerators and propeller-aspirator-pumps are the most common aerators used in
aquaculture. Aeration amounts varies from 1-2 kW ha -1 in extensive cultures, to 15-20 kW
ha -1 in intensive culture of marine shrimp. For every kW of aeration extra, the gains are
estimated over 500 kg fish/crustacean biomass (Boyd, 1998).
All basic types of mechanical aerators have been used in aquaculture, but vertical pumps,
pump sprayers, propeller-aspirator-pumps, paddle wheels, and diffused-air systems are the