Prebiotics in Global and Mexican Fish Aquaculture: A Review.

Continued human population growth has resulted in increased demand for products, including those derived from aquaculture. The main challenge in aquaculture is producing more every year. In recent years, environmentally friendly supplements that provide the necessary pathways for optimal production have been emphasized. One of them is prebiotics, selectively utilized substrates by host microorganisms conferring a health benefit. Interest in applying prebiotics in global fish farming has increased in recent years as it has been shown to improve growth, boost the immune system, resist stress conditions, and cause the modulation of digestive enzymes. These effects reflect reduced production and disease costs. However, in Latin American countries such as Mexico, large-scale use of these food supplements is needed as a sustainable alternative to improve fish production. This paper gives a review of the current advances obtained with the application of prebiotics in commercially farmed fish worldwide, mentions the prebiotics to use in the aquaculture industry, and updates the status of studies about the used prebiotics in global commercial fish cultivated in Mexico, as well as freshwater and marine endemic fish in this country. Also, the limitations of prebiotics application in terms of their use and legislation are analyzed.

Internal phosphorus load in a Mexican reservoir through sediment speciation analysis.

Since the sequential extraction of phosphorus (P) in sediment makes it possible to determine the P potentially available for release, in this paper, we evaluate the fractions of P in sediment profiles from Valle de Bravo reservoir, a eutrophic lake in central Mexico to determine the contributions of each fraction to the internal P load (IPL). The P fractionation scheme employs sequential extractions of sediment with O2-free water (MilliQ), bicarbonate-dithionite (BD), sodium hydroxide (NaOH), hydrochloric acid (HCl), and potassium persulfate (K2S2O8-) to obtain five P fractions. A monitoring of redox potential (Eh), pH, and total phosphorus (TP) in the bottom water of the reservoir indicated variations of these parameters during the year, observing that as Eh decreased, the P concentration increased, it was also observed that when increasing pH, P concentration also increased. Analyzing the behavior of fractions of P in sediment profiles, we found that the dominant fractions are those bound to iron and aluminum oxides, corresponding to approximately 50% of total P since P concentrations of these fractions were twice as high in the top 5 cm of the sediment profiles and decreased with increasing depth. Considering the variations of Eh and pH in the bottom water of the reservoir and that these parameters are factors that control the release of P with the fractions of P bound to Fe/Mn and Al/Fe oxides, we concluded that these fractions contribute most to P potentially available for release in the reservoir, representing a possible IPL of 23.5 ± 1.4 t/year.

Internal phosphorus load in a Mexican reservoir: forecast and validation.

To determine the internal phosphorus load (IPL) as a function of redox potential (Eh) in a Mexican reservoir, the results from a phosphorus (P) release experiment were extrapolated to temporal and spatial variations of Eh in sediments, and an IPL-Eh of 24.2 ± 2.5 t/yr was obtained. This result is compared with the P mass balance (MB) in the reservoir, where the IPL-MB is determined as the difference between P inputs to the reservoir and the outputs. Inputs of P are the sum of the external P load from the hydrological basin, the IPL, and P in atmospheric precipitation; outputs of P are the sum of sedimented P, and the removal of P in water and biomass, and the resulting IPL-MB, is 26.4 ± 4.9 t/yr. In addition, P concentrations in sediment cores (SCs) are analyzed, and the historical release of P from sediments determined, resulting in an IPL-SC of 23.5 ± 1.4 t/yr. The different IPL results are similar, as average values are within the standard deviation of IPL-MB. It is concluded that analysis of the variations in Eh in sediments allows determination of the reservoir's IPL. Six-weekly IPL-Eh and IPL-MB values are analyzed, and it can be seen that IPL occurs mainly during the period from May to August, when the water column is thermally stratified.