This study was conducted to investigate the effects of dietary fructooligosaccharides (FOS) on the growth, survival rate, digestive enzyms activity, and the expression of intestinal barrier function genes in tropical gar (Atractosteus tropicus) larvae. A total of 960 larvae (0.030 ± 0.006 g) were fed three diets supplemented with increasing FOS concentrations (2.5, 5, and 7.5 g kg⁻¹) and a control diet for 15 days. Results revealed that a 7.5 g kg⁻¹ FOS supplementation improved weight gain, specific growth rate, and survival rate (p < 0.05). Furthermore, 5 g kg⁻¹ FOS supplementation increased alkaline protease and amylase activities and induced an upregulation of the claudin-17 gene expression (p < 0.05). Meanwhile, the inclusion of 7.5 g kg⁻¹ FOS induced the upregulation of mucin 2 (muc-2), and the tight junction genes zo-2 and claudin-3 (p < 0.05). In addition, 2.5, 5, and 7.5 g kg⁻¹ FOS promoted the downregulation of the claudin-15 gene expression (p < 0.05). At the same time, FOS inclusion did not increase the pro-inflammatory cytokine il-8 expression. We can conclude that 7.5 g kg⁻¹ FOS supplementation improves growth performance, survival rate, and digestive capacity, and could contribute to the reinforcement of the intestinal barrier function of Tropical gar larvae.

Probiotics in aquaculture hold promise for enhancing fish health and growth. Due to their increased specificity and affinity for their host, indigenous probiotics may offer isolated and potentially amplified benefits. This study investigated the effects of Lactococcus lactis PH3-05, previously isolated from adults of tropical gar (Atractosteus tropicus), on the growth, survival, digestive enzyme activity, intestinal morphology, expression of barrier and immune genes, and intestinal microbiota composition in the larvae of tropical gar. Larvae were fed with live L. lactis PH3-05 concentrations of 10⁴, 10⁶, and 10⁸ CFU/g for 15 days alongside a control diet without probiotics. Higher concentrations of L. lactis PH3-05 (10⁶ and 10⁸ CFU/g) positively influenced larval growth, increasing hepatocyte area and enterocyte height. The 10⁶ CFU/g dose significantly enhanced survival (46%) and digestive enzyme activity. Notably, the 10⁸ CFU/g dose stimulated increased expression of muc-2 and il-10 genes, suggesting enhanced mucosal barrier function and anti-inflammatory response. Although L. lactis PH3-05 did not significantly change the diversity, structure, or Phylum level composition of intestinal microbiota, which was constituted by Proteobacteria, Bacteroidota, Chloroflexi, and Firmicutes, an increase in Lactobacillus abundance was observed in fish fed with 10⁶ CFU/g, suggesting enhanced probiotic colonization. These results demonstrate that administering L. lactis PH3-05 at 10⁶ CFU/g promotes growth, survival, and digestive health in A. tropicus larvae, establishing it as a promising indigenous probiotic candidate for aquaculture applications.

The effect of adding inulin to balanced diets for tropical gar (Atractosteus tropicus) larvae on growth, survival, digestive enzyme activity, and antioxidant activity was evaluated. The diets were supplemented with 0.5, 1.0, 1.5, 2.0, and 2.5% inulin in addition to a control diet (0% inulin). A total of 1800 larvae of A. tropicus distributed in 18 tanks were used; the larvae were fed five times a day (8:00, 11:00, 13:00, 15:00, and 18:00) with Artemia nauplii from the absorption of the yolk (from 3–7 days after hatching, DAH) up to 10 DAH, which was mixed with the experimental feeds from 8–11 DAH (co-feeding) and exclusively with the balanced diets from 12 DAH to 21 DAH. Larvae fed the control diet (0% inulin) had the highest growth in weight and length, followed by fish fed the 2.5 and 2.0% inulin inclusions. However, survival showed that the fish fed with the inclusion of 2.5% inulin had the highest percentage (34.7%) compared to the rest of the treatments. On the other hand, the highest digestive enzymatic activities (acid and alkaline proteases, amylase, and lipase) were recorded in the larvae fed with 2 and 2.5% inulin. Likewise, catalase (CAT) and superoxide dismutase (SOD) activities were higher in larvae fed the control diet with 0% inulin. Supplementation of 2.0% to 2.5% inulin in the diet is recommended for A. tropicus larvae as it improves survival and digestive enzyme activity during this early stage of life.

Mannan-oligosaccharides (MOS) are non-digestible carbohydrates, and their use in aquaculture as prebiotics is well documented. The objective of this work was to test whether MOS supplemented in the diet of A. tropicus larvae (2, 4, and 6 g kg⁻¹) influence growth parameters, the activity of digestive enzymes, and the expression of genes related to the intestinal barrier. The highest total length was observed in larvae fed 6 g kg⁻¹ MOS compared to control larvae. Trypsin activity increased with the addition of MOS to the diets, but leucine aminopeptidase activity only increased with 6 g kg⁻¹ MOS. Lipase and α-amylase activities increased in larvae fed with 2 and 4 g kg⁻¹ MOS. The expression of zo-2 was higher with the 6 g kg⁻¹ MOS treatment. The cl-3 transcripts were lower with 2 g kg⁻¹ MOS but higher with 6 g kg⁻¹ MOS. All tested concentrations of MOS increased the expression of muc-2. In this study, incorporating mannan-oligosaccharides into the diet of A. tropicus larvae had a positive effect, and the concentration of 6 g kg⁻¹ produced the best results. Therefore, including this prebiotic in the diets for the culture of A. tropicus larvae is suitable.

Mexico is responsible for the protection and management of a large number and variety of aquatic bodies of national and international importance. Environmental pollution by so-called persistent and bioaccumulative toxic substances (PBTS) poses significant risks for all of the world's aquatic ecosystems, especially in countries with emerging economies, where environmental regulations are often poorly implemented. In Mexico, the development of industrial projects and the deficient application of environmental regulations, together with the rapid increase in population and the inefficient disposal of urban waste, have generated a severe problem of water pollution in the country. National environmental protection programs have not included the monitoring of PBTS, even though researchers have been monitoring the main aquatic ecosystems of the country for nearly three decades, generating valuable information that could help improve the protection and exploitation of these ecosystems. The present work reviewed a large portion of the available literature (~150 articles) on aquatic biomonitoring of the main PBTS (Hg, Cd, Pb, POCs, and PCBs) in Mexico. This work aims to collect, synthesize, and facilitate the management and interpretation of the reported data to improve the country's aquatic ecosystems' protection and management.