Auburn University - Bruce and Kelly Labs
Auburn University - Bruce and Kelly Labs
Dr. Tim Bruce and Dr. Anita Kelly
Uthpala M. Padeniya, D. Allen Davis, Timothy J. Bruce
Auburn University, School of Fisheries, Aquaculture and Aquatic Sciences, Auburn, AL 36849
Applying probiotics in aquaculture has been a common way of controlling diseases that arise with the intensification of aquaculture production. The present study aimed to examine the effects of the dietary inclusion of commercial yeast products on growth performance, resistance against Flavobacterium oreochromis, and innate immunity in Nile tilapia (Oreochromis niloticus). A basal diet containing 32 % crude protein and 8% lipid was considered as a control (Con), and two other diets were produced by including DVAQUA® (Diamond V Mills, Inc., IA, USA) at 2% inclusion rate and NutriTek® (Diamond V Mills) at 1g kg-1. At trial initiation, nine polyethylene tanks (3750L) were randomly assigned to one of the three dietary treatments in three replicates (190 fish per tank; 570 fish per treatment). The trial was carried out in biofloc water in an aquaponics greenhouse setting. The fish were fed 5% body weight with the test diets twice daily for 16 weeks. Fish were subjected to a disease challenge (immersion) after 16 weeks of the feed trial against the Gram-negative bacterium Flavobacterium oreochromis (R18-27).
At the end of the trial, growth parameters, including final tank biomass, mean weight, weight gain, FCR, or survival, were not different between the treatments. For the F. oreochromis challenge (3.9 x 106 CFU mL-1 immersion dose; 8 days), each treatment diet had three tank replicates, and one mock tank was used as the control. The challenge trial was conducted for eight days. At the end of the challenge, cumulative percent mortality was measured. The fish fed with DVAQUA® (33%) and NutriTek (24.3%) had significantly higher endpoint mortality than the control group (63%; P=0.048). Kaplan-Meier survival analysis with a log-rank test detected differences between the control and DVAQUA® (P<0.001) and control and NutriTek® (P<0.001), the two diets with fermented yeast products. Serum lysozyme activity (pre- and post-challenge) was analyzed using two-way ANOVA, but no differences were found for Treatment or Time effects with no significant interaction. It is evident from this experiment that the inclusion of fermented yeast products as a form of probiotics to fish feed increases the resistance to Flavobacterium oreochromis in Nile tilapia when reared in biofloc systems. Gene expression analyses of pre-challenge and post-challenge samples are underway to further confirm the mechanisms of the fish immune response in the spleen and kidney tissues. The challenge trial data shows that fermented yeast products as probiotics protect against F. oreochromis infection in Nile tilapia.
Jamison L. Semla1, Ian A.E. Butts1, Donald A. Davis1, Benjamin R. LaFrentz2, Timothy J. Bruce1
1School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, 36849, USA
2USDA-ARS Aquatic Animal Health Research Unit, Auburn, AL, 36830, USA
Largemouth bass (LMB) is an important sportfish and culture practices have led to the potential of this species as a foodfish. For aquafeeds, many industry segments heavily on fishmeal (FM) as a primary source of protein in dietary formulations. Although an excellent protein source, FM is subject to supply shortages, increased consumer demand, and variable pricing. New dietary protein sources, such as soy products, have the potential to replace FM but may also influence growth performance and health in several aquaculture species. To evaluate the potential of soybean process variants in largemouth bass diets, a feeding trial was conducted using three experimental diets with a thirty percent replacement of fishmeal with soybean meal, a soy protein concentrate, or fermented soybean meal. The study evaluated growth performance, gastrointestinal health, and disease susceptibility to columnaris disease in Florida LMB fingerlings. Sixteen individual tanks within a recirculating aquaculture system (RAS) were stocked with fifty LMB fingerlings (6.1 ± 0.1g), and the fish were fed the three experimental diets or a basal (fishmeal-based) diet for 14 weeks. At the conclusion of the trial, fish were sampled for blood (sera lysozyme and chemistry), intestines (gene expression), and intestines (microbiome and histological examination) to assess health parameters. Quantitative histological differences were found in the height (P < 0.001) and thickness of folds (P = 0.002), and the thickness of the lamina propria sections (P = 0.004). Qualitative histological differences were not found in the thickness of the lamina propria (P = 0.858), connective tissue beneath folds (P = 0.588), and vacuolization (P = 0.344). Gene expression analysis of targeted cytokines in the intestine found no differences for il-1b (P = 0.611), il-8 (P = 0.813), il-10 (P= 0.347), and tgf-b (P =0.349). At the end of the feeding trial, LMB were subjected to an immersion challenge with a low dose of Flavobacterium columnare (ARS-LMB-23-5, 4.98 x 106 CFU mL-1). Endpoint CPM model, there was no statistical difference (P = 0.999), but there was a statistical difference in Kaplan-Meier survivability (P <0.001). All diet groups were susceptible to infection and experienced mortality, but the soy protein concentrate diet displayed the most significant survivability during the immersion bacterial challenge. This study demonstrates the potential of partially replacing FM with soy protein in LMB fingerlings. The evaluated diets showed comparable growth performance, with only some mild effects on the gastrointestinal system. Thus, LMB producers can potentially reduce feed costs to maximize profits.
Abdulmalik A. Oladipupo, Anita M. Kelly, D. Allen Davis, and Timothy J. Bruce
School of Fisheries, Aquaculture, and Aquatic Sciences, 203 Swingle Hall, Auburn University, Auburn, AL 36849
Previously, a commercial humic substance (HS) and protease complex (PC) additives within juvenile channel catfish diets have demonstrated potential for disease resistance and promoting growth in an indoor experiment. These immunomodulatory compounds present an economically feasible disease treatment option for U.S. catfish producers. The efficacy of immunostimulants has often been associated with modulating the intestinal microbiota, which in turn may influence fish growth and health. In addition, environmental imbalance and diverse microbial populations are critically important factors that interact in outdoor production systems, making a controlled indoor trial sometimes challenging to make inferences for commercial production. The current study aimed to investigate the effects of dietary PC or HS on the intestinal microbiota of channel catfish reared in a commercial rearing environment.
In this trial, sub-adult catfish were continuously fed HS or PC-supplemented diets in outdoor pond-fed flow-through tanks in Greensboro, AL. Over a 60-day feeding period, we evaluated the influences of these products on the catfish gut microbiota and health parameters. The feeding trial was conducted using twelve 800 L circular flow-through tanks supplied by water from a 0.4 ha earthen pond. Channel catfish juveniles (67.1±1.0g) were fed a control diet (28%) or supplemented diets (PC or HS; 28%) in four replicates. Blood samples were collected for sera lysozyme activity and gut fecal samples for microbiome evaluation at mid-point (30 d) and end-point (60 d) to discern community differences across time and treatments.
After the 60-day study, both HS and PC catfish groups exhibited higher survival rates than the control group (P=0.006). Using 16S rRNA sequencing and analysis, we discerned that bacterial richness was similar across groups at 30 d (P>0.05) but significantly reduced in the C28+HS after 60 days compared to C28+PC (P=0.015). Conversely, bacterial community evenness significantly increased following 30 days of HS feeding (P=0.043) than C28+PC or C28. The overall composition and beta diversity (Bray-Curtis and Unweighted Unifrac) differed between the PC and HS groups, and Unifrac distances exhibited no correlation with the administration time (P>0.05). In the Bray-Curtis distances comparison, a significant time-treatment interaction was found (P=0.041). However, permutational multivariate analysis of variance showed a significant separation in community composition between C28+HS and C28+PC (P=0.004) or C28 (P=0.004) at 30 d. Bacteria from the phylum Firmicutes were overwhelming in the gut of catfish fed PC after 30 d, while the family Fusobacteriaceae were highly enriched in HS (73%) and control-fed catfish (78%). Sera lysozyme activity was also enhanced in HS and PC diet at 30 d (P=0.024) with no further increase at 60 d. Combined, these results demonstrated that dietary HS or PC could impact intestinal microbial diversity in channel catfish over a short-term application. However, these changes could influence catfish growth, immunity, and survival in catfish production environments.