Alleviation of aflatoxin B1 (AFB1) toxicity by calcium bentonite clay: Effects on growth performance, condition indices and bioaccumulation of AFB1 residues in Nile tilapia (Oreochromis niloticus)

Previous research has shown some success using clay-based binders to adsorb aflatoxin in terrestrial animal feeds; however, no adsorbent has been approved for the prevention or treatment of aflatoxicosis. In the present study, growth performance, condition indices, proximate composition and protein retention efficiency of Nile tilapia were evaluated along with analysis of aflatoxin-B1 residuals in muscle tissues of fish fed diets containing AFB1 at 2 and 4 ppm along with either 0.5 or 1.0% calcium bentonite clay (4TX) for a period of 10 weeks. To compare the efficacy of inclusion type of 4TX clay in the diet, it was added as either a dry powder mix (PM) or water dispersed (WD) form. Inclusion of AFB1 at concentrations of 2 and 4 ppm significantly (P < 0.05) reduced weight gain, feed efficiency ratio (FER), hepatosomatic index (HSI), muscle ratio, whole-body crude lipid and protein retention efficiency (PRE), regardless of the inclusion of 4TX in the diets. However, addition of 4TX as PM in the diet improved some of those fish responses. In particular, at the 2 ppm AFB1 level, 1.0% 4TX PM tended to improve % weight gain (831%) as compared to 1.0% 4TX WD (707%) or 0.5% 4TX WD (708%). Also there was a significant difference in HSI when contrasted between basal vs clay PM (P < 0.001) and dispersion type, WD vs PM (P = 0.022). Whole-body % moisture (P = 0.036) and crude lipid (P = 0.014) also were significantly affected by AFB1 in diets at both 2 and 4 mg/kg. Contrast between basal vs clay WD also showed a significant difference (P = 0.046) in whole-body crude lipid content. The AFB1 residues in muscle tissues were only detected in fish exposed to the highest inclusion level of AFB1 (4 ppm). Addition of 4TX in the diets significantly reduced bioaccumulation of AFB1 in muscle of Nile tilapia, especially when included in PM (0.43 ± 0.03 ng/g) compared to WD (1.87 ± 1.32 ng/g) form. Thus, greater efficacy of 4TX clay was observed when included as PM compared to WD in alleviating AFB1 induced toxicity in tilapia.