Take some guts, a few bacteria species and throw in some brains while you are at it…and what does that give you? One of the most unexplored interactions that has scientists all riled up: how the bacteria population in the gut, known as the gut microbiome, interacts with the brain to allow the animal to grow and adapt to stress in its environment. And this interaction could not be more relevant than it is for farmed fish, where overcrowding, waste generated by the animals and increasing global temperatures are just some of the stressors that the fish can endure. How can fish farmers increase production in a sustainable way, yet minimize the adverse conditions that the fish may encounter? Is it possible to manipulate the diversity of the gut microbiome to improve the overall health and growth of fish in aquaculture? Can we make them bigger, faster, healthier – and do it at a lower cost?
Victor Alfonso Castaneda-Monsalves from Universidad Nacional de Colombia in Medellin and his colleagues set out to identify the species of bacteria living in the gut of the third most cultured fish in Colombia, the white cachama (Piaractus brachypomus). For their work, the group compared both juvenile and adult fish. Wanting to differentiate between the anterior (mouth to stomach) and the posterior (intestine) gut, the authors separated the sections and compared the bacteria species in each at both life stages. Initially, the team found that bacteria known as Firmicutes, Spirochaetes and Fosobacteria – which are involved in fermentation, breakdown of plant products and immune protection – occur in both life stages of the white cachama. However, Fusobacteria dominated the front section of juvenile intestines, while Spirochaetes dominated in the posterior. In contrast, Fusobacteria and Firmicutes dominated the population of the entire adult gut. As members of the Fusobacteria family produce vitamin B12 during digestion, the authors suggested that their presence could eliminate the need to supplement the fish diet with vitamin B12, therefore cutting down costs to the fish farmer.
In addition, the team found that probiotic bacteria, which boost the immune system to fight infections, occurred in the fish guts, although they were more dominant in the adult intestines than in those of the juvenile fish. However, the researchers also discovered Proteobacteria in the guts of all farmed fish, which can cause infections if the animals are stressed. They suggested that manipulating the ‘good’ probiotic bacteria in the fish digestive systems could allow them to outcompete the ‘bad’ ones, as well as boosting the immune system to reduce infection and promote growth.
The idea of an interaction between the microbiome and the brain is not new, but how they interact and to what degree bacteria in the gut can influence how the brain responds to stress is still a mystery that we are only now beginning to unravel. Exploring this question in the context of aquaculture opens new possibilities for food production. Can we improve the health of the fish by simply manipulating the population of the bacteria growing in their intestines? Can we improve the taste of the meat? Can we make fish grow faster, reproduce sooner and at high rates, to increase production? These are just some of the questions that are worth exploring, as the human population continues growing and the global demand for fish is ever increasing.