Intensive fish culture is a practice in aquaculture systems; however, it can produce negative environmental impacts due to the accumulation of organic nitrogen from feeding procedures, but also from fish wasting products. Recirculating aquaculture systems have emerged as one strategy to reduce these impacts, maintaining a healthy environment for fish. These reduce toxicity level through nitrifying biofilters, which use a microbial consortium to convert ammonia into nitrate. The main component of bacterial consortium is comprised by aerobic ammonia‐oxidizing bacteria and aerobic nitrite‐oxidizing bacteria, which are part of the whole nitrification process. These nitrifying bacteria grow in suspension or in fixed form, the latter characterized by a biofilm formation where bacteria adhere to a physical substrate in a self‐produced polymer matrix. The biofilm formation requires tight communication among bacteria to regulate the transcriptional circuits underlying the production of chemical signal molecules (e.g. N‐acetyl‐homoserine lactones) that control biofilm formation. This coordination is known as quorum sensing and can be considered as a mechanism that contributes to the coupling and maintenance of nitrification rate among bacteria by regulating expression levels of relevant genes associated with nitrification process. Therefore, the control of this process is crucial in recirculating aquaculture systems and its incorrect manipulation can produce a detriment of water quality. We here present an overview of the nitrification process in recirculating aquaculture systems. Subsequently, we describe nitrifying biofilters and nitrifying bacteria. Finally, we discuss how quorum sensing controls the efficiency of nitrifying bacteria and potential applications of nitrifying biofilters in intensive aquaculture systems.

Among brooding species, passive and active means to provide oxygen to embryos can be observed. Among passive oxygen providers, lower oxygen availability in the center than at the periphery of embryo masses seems to delay development of inner embryos. We investigated the differences in patterns of oxygen supply to the periphery and the center of embryo masses in two active oxygen providers, the brachyuran crabs Cancer setosus and Homalaspis plana, and evaluated the consequences on: (1) the proportion of time that earlyand late-stage embryos were exposed to low or high oxygen partial pressure (PO 2 ), (2) oxygen consumption of the embryos from the center (inner) and the periphery (outer) of the embryo mass at those PO 2 levels that the embryos experience throughout development, and (3) development of inner and outer embryos. We found that oxygen availability in the embryo masses of brachyuran crabs exhibited dramatic contrasts between the periphery and the center during early development and that these differences decreased throughout embryonic development. These dissimilar patterns of oxygen availability produced differences in the proportion of the time that the embryos were exposed to high and low PO 2 levels throughout development. PO 2 affected oxygen consumption of the inner and outer embryos in the same fashion, but the oxygen demand of inner embryos was lower. Furthermore, development of inner embryos was delayed, in comparison to outer embryos of the same female. We suggest that the asynchrony in the development of inner embryos, in comparison to outer embryos, is due to oxygen limitation, since oxygen availability affects embryonic oxygen consumption. The differences between development of inner and outer embryos is relatively small, when compared to other marine invertebrates, probably because female crabs are able to adjust oxygen supply to the embryos according their needs, while passive oxygen providers are not. However, active oxygen provision may affect investment in reproduction. Our results could have important implications both on studies of larval development and survival and in understanding the life-history tradeoffs of aquatic invertebrates.

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The current study describes the taxonomic and functional composition of metagenomic sequences obtained from a filamentous microbial mat isolated from the Comau fjord, located in the northernmost part of the Chilean Patagonia. The taxonomic composition of the microbial community showed a high proportion of members of the Gammaproteobacteria, including a high number of sequences that were recruited to the genomes of Moritella marina MP-1 and Colwellia psycherythraea 34H, suggesting the presence of populations related to these two psychrophilic bacterial species. Functional analysis of the community indicated a high proportion of genes coding for the transport and metabolism of amino acids, as well as in energy production. Among the energy production functions, we found protein-coding genes for sulfate and nitrate reduction, both processes associated with Gammaproteobacteria-related sequences. This report provides the first examination of the taxonomic composition and genetic diversity associated with these conspicuous microbial mat communities and provides a framework for future microbial studies in the Comau fjord.