Microminerals are essential nutrients for fish and play key roles in their normal metabolism. Among these elements, iron is related to several biochemical processes including oxygen transport, electron transfer, and energy metabolism. As an alternative approach to the use of bulk minerals, the use of elemental nanoparticles in animal nutrition has gained attention due to their increased surface area, which can potentially improve their bioavailability. In addition, acidifiers are commonly supplemented in fish feeds to improve weight gain, and they can synergistically interact with minerals, thereby enhancing their bioavailability. Commercial catfish feed mills have been supplementing feeds with high iron concentrations to mitigate idiopathic catfish anemia. Therefore, the aim of this study was to better understand the effects of high iron concentrations in catfish feed, the supplementation of iron nanoparticles, and the possible interaction between the nanoparticles and calcium propionate on catfish growth and health parameters.
Two different sources of iron, bulk iron (FeSO4.H2O) and nanoparticles (Fe 60 to 80 nm, 99.7% purity) at 1000 mg/kg, and two levels of calcium propionate supplementation (with and without calcium propionate, at 0.25%) were evaluated using a 2x2 factorial design. An additional control diet without iron or calcium propionate supplementation was included in the feeding trial which was conducted in a recirculating aquaculture system for 9 weeks. A total of 750 catfish fingerlings (average weight 1.9 ± 0.1 g) were distributed in 25 aquariums (110 L; 30 fish/tank). At the end of the feeding trial, growth performance, whole-body proximate, blood parameters, intestinal microbiota, and intestinal histology were evaluated. The remaining fish were subjected to a bacterial challenge using a virulent strain of atypical Aeromonas hydrophila (ML09-119) and survival was monitored for 72 hours. A separate digestibility trial was carried out for 5 weeks. Three hundred juvenile catfish (average weight 50.3 ± 2.3 g) were distributed in five tanks (400 L), operating as a recirculating aquaculture system. Each experimental diet was assigned to one tank for one week, and the assigned experimental diet of each tank alternated every week until all tanks receive all experimental diets. Fecal material was collected using a modified Guelph method. For the growth study, calcium propionate supplementation negatively impacted fish weight gain, and the interaction between nano iron and calcium propionate reduced catfish RBC. Hematocrit was significantly affected by dietary iron sources, where fish fed bulk iron (43.7 ± 3.6%) had higher values to fish fed nano iron (40.6 ± 2.3%). The intraperitoneal fat was higher in fish fed the nano iron-containing diet (3.4 ± 0.4%) compared to bulk iron (2.9 ± 0.2%). There were no differences in iron digestibility, whole-body proximate composition, protein conversion ratio, intestinal microbiota, or survival after bacterial challenge. In conclusion, dietary calcium propionate negatively affected the weight gain and RBC of channel catfish. Furthermore, iron nanoparticles decreased the blood hematocrit, negatively interacted with calcium propionate for RBC, and increased the visceral fat index. The histology of the intestine is currently being analyzed and will be presented during the conference.