Stocking density in aquaculture: Tips to consider

When we start our project or begin to work in fish production and our knowledge is basic, we usually have many doubts and concerns, among them how many fish we should plant or how much density (Kg/m3) we can keep in our pond or production unit.

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    Zootechnical aspects

    To determine the density of our production we must know the zootechnical or biological needs of the species we want to cultivate or produce, for example, fish from warm waters support low oxygen concentrations much better. The red Tilapia (Oreochromis sp) survives in waters with oxygen concentrations between 4 – 5mg/l, on the other hand in the culture of trout (Oncorhynchus mykiss) which is a cold water fish, a concentration of 5.5mg/l already begins to generate much stress in the animal and mortalities start to occur. In addition to oxygen, we must also take into account other parameters such as pH and temperature as a starting point. The more information we have about the quality of the water where we want to keep our fish, the easier it will be for us to make decisions.

    Other considerations

    The production density will not only depend on the species we want to produce but also on the stages we are working with, the densities are not the same for producing fry as for fattening fish. Density is one of the factors that will determine growth rate (SGR), feed efficiency (FCR) and feed rate (SFR).

    In our experience linked to primary production, we have participated in projects where we have carried out the conversion process from conventional to organic production under European regulations, going from producing densities of 40Kg/m3 to 25Kg/m3. The first thought that may come to mind is that we are losing money because we are producing less. We share our experience with you, after one production cycle mortality went from 20% to 5%, before the conversion oxygen was applied to the ponds to maintain that higher density, in ecological with lower density oxygen consumption was reduced by 90%, the fish had a better FCR, This was because the fish were less stressed, there was less competition for food and this was also reflected in better growth, going from an SGR of 0.75 to 2, there was less size dispersion, this resulted in less management, as the number of classifications was reduced. The occurrence of pathologies was reduced, the fish had more space to swim, they went from having a higher percentage of visceral fat to more muscle and more intramuscular fat, which gave better quality meat.

    Conclusions

    In conclusion, often less is more, we can have our ponds with very high densities, injecting oxygen or aerating the water with different systems, but it is very likely that our fish are stressed, which affects their immune system and therefore have a higher probability of developing a pathology and we have to medicate them. It is also very possible that we are overfeeding and affecting the quality of the water and loading the bottom with nutrients. That is why it is important to find the balance point and for this it is necessary to have data, if our FCR, SGR, SFR coefficients are good and we have a low mortality, I would say that we are on the right track.

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