Use of probiotics in aquaculture
Probiotics are well known and routinely used additives in the main livestock species. They claim to improve gut health by stabilizing gut flora being their effect reflected in a better overall health status, welfare and performance of the animals.
In aquaculture, probiotics are administered by feed and/or as a water additive. The supplementation of probiotics through feed is a better method to ensuring the efficiency of the probiotic bacteria in the GI tract of fish. However, their use in fish feed production is still scarce.
Different factors might be behind the lack of this type of products for aquaculture: (i) The digestive system of fishes differs between cultured species, and gut microbiota may vary considerably among individuals of one specie, under the same rearing conditions;(ii) Probiotics used in monogastric and ruminants available nowadays are mainly based on bacteria or yeast that need enough warm temperature to develop in the animals’ gut. It can be difficult to reach taking into account that fish are poikiloterms and in some specific productions water temperature is extremely low; (iii) Up today, it is not well known if the microorganisms from probiotics can develop, multiply as well as modify fish gut flora in these environmental and gut conditions and, (iv) Feed fish processing is extremely hard in terms of temperature and pressure so, how to apply this alive microorganism to fish pellets is still being studied. Their inclusion by coating after pelleting can be the solution, although the stability of this microorganism in this oily solutions as well as once reach water in tanks or sea need still to be demonstrated.
Despite all this, the application of probiotics in aquaculture practices has already gained momentum, and nowadays, numerous microorganisms, both from indigenous and exogenous sources, are used as probiotics. The commonly used probiotics in fish culture practices belong to Saccharomyces, Clostridium, Bacillus, Enteroccus, Lactobacillus, Shewanella, Leuconostoc, Lactococcus, Carnobacterium, Aeromonas and several other genera.
In the European Union, there is still only one probiotic based on the lactic acid bacteria strain Pediococcus acidilactici that has been agreed as aquafeed supplement, after demonstration of beneficial effects on salmonids and shrimps. In some other countries, especially in Asia, many other probiotics are available for aquaculture.
The expected benefits may vary. For example, increased survival and production of channel catfish (Ictalurus punctatus) by Bacillus species, improved growth and immunity of Nile tilapia (Oreochromis niloticus) by Bacillus subtilis and Rhodopseudomonas, and protection of rainbow trout (Oncorhynchus mykiss) against Vibrio anguillarum by Pseudomonas fluorescens have been demonstrated. More generally, probiotics have shown that they can help to increase fish growth by enhancing the feed conversion efficiency, as well as confer protection against harmful bacteria by competitive exclusion, production of organic acids (formic acid, acetic acid, lactic acid), hydrogen peroxide and several other compounds. They can also effectively trigger the piscine immune system. For all this reasons, their use will definitively increase in the near future.