Capitulo de libro
USE OF YEASTS AS PROBIOTICS IN FISH AQUACULTURE
SUSTAINABLE AQUACULTURE TECHNIQUES
Registro en:
11110414
978-953-51-1224-2
Autor
Navarrete Wallace, Paola Alejandra
Tobar Ramirez, Davier
Institución
Resumen
According to the UN Food and Agriculture Organization (FAO), “aquaculture, probably the fastest growing food-producing sector, now accounts for nearly 50 percent of the world's food fish” [1]. However, production is hampered by unpredictable mortalities that may be due to the negative interactions between fish and pathogenic bacteria. Intensive fish farming has resulted in a problematic growth in bacterial diseases, prompting the necessary and intensive use of antimicrobials for their treatment.
Because of the rapid expansion of aquaculture, a limited supply of fishmeal has the potential to impede the future growth of this industry. Consequently, much effort has been given to studying other protein and oil sources, but finding a suitable alternative has proved to be challenging. Among the alternatives, plant-based formulations are the least expensive, and many such formulations have a suitable protein profile and long-term availability. Oilseeds, in particular soybean and grain products, have great potential as alternative sources of fish feed. Soybeans are rich in protein and represent the most commonly used plant protein source on the world market. Soybean meal (SBM) has already become an important protein source in fish feed. However, the inclusion of some vegetable proteins, such as SBM, in the diets of fish at levels of >20% may induce intestinal disorders including pathomorphological changes in the distal intestinal epithelium accompanied by diarrhea [2, 3], sometimes caused by the anti-
nutritional factors that are present in SBM. The addition of probiotics (acid lactic bacteria) to starter diets appeared to improve SBM utilization in first feeding rainbow trout [4]. In this context, two of the major challenges in fish aquaculture facilities are 1) the control of diseases, especially during the earliest life stages, and 2) the improvement of nutrition by optimizing food utilization, especially for new fish species. It is well recognized that the bacterial microbiota of fish is beneficial to the host and affects
important biological processes, including nutrient processing and absorption, the develop-ment of the mucosal immune system, and angiogenesis, as was demonstrate in gnotobiotic mice. In larval gnotobiotic zebrafish studies, was shown that the microbiota also influences enterocyte morphology and epithelial renewal, host-transcriptional responses to the microbiota regarding epithelial proliferation, nutrient and xenobiotic metabolism, and immune responses [5].
Yeast have been identified as part of the normal microbiota of both wild and farmed fish, and their role in fish health and nutrition has been addressed in the literature, as yeast have been used either alive to feed live food organisms or after processing as a feed ingredient after demonstrating an artificial colonization of the intestinal host.
Even when accounting for less than 1% of the total microbial isolates in the host, yeast can represent a major physiological contribution beyond what has been observed for probiotic bacteria; in fact, cell volumes from yeast may be larger than those of bacteria by a hundredfold [6]. In contrast to bacteria, yeast cells utilize a wide spectrum of simple and more complex organic compounds. This phenomenon results from the extensive metabolic potential of yeast, which is reflected by the production of diverse enzymes. Polyamines secreted by yeasts are also involved in the maturation of the digestive tract of fish larvae. Furthermore, some yeastspecies and their components, such as ?-glucans and mannoproteins, can stimulate the immune and antioxidant systems of the host. Understanding the participation of yeast microbiota in fish health and nutrition may improve both the sanitary conditions and the production performance of fish. The aim of this chapter is to describe the current knowledge regarding the use of yeasts as probiotics in aquaculture systems. The chapter will include a recent review on the presence and diversity of yeast in marine and aquaculture systems, focusing on the yeast diversity found in the fish gut microbiota. The chapter will also include basic information on the molecular methods used for yeast identification. Finally, the chapter will emphasize topics related to the essential role of probiotic yeasts used in disease control and nutritional improvements in aquaculture, with a special focus on the beneficial effects of yeast ?-glucans. FONDECYT 274 FONDECYT