The mitigating effect of Spirulina (Arthrospira platensis) on the hemotoxicity of gibberellic acid on juvenile tilapia (Oreochromis niloticus)

Abstract

The use of plant growth regulators has led to environmental contamination of water bodies that occur adjacent to agricultural areas. Some of these chemicals are bioactive, not only to plants, but also to non-target exposed biota, namely of the aquatic compartment. Previous work demonstrated the establishment of hepato- and nephrotoxic effects in juvenile tilapia (Oreochromis niloticus) exposed via aquatic media to gibberellic acid (GA₃), which is among the most used plant growth regulators, in agricultural practices. Here, we investigated the effect of GA₃ on hematological indices, poikilocytosis, nuclear abnormalities, and genotoxic indices measured in Nile tilapia (Oreochromis niloticus), as well as the putative protective effects of dietary supplementation of Spirulina (Arthrospira platensis). Fish were evenly assorted into 5 groups: group I served as a control, and groups II-V were fed diets supplemented with Spirulina at rates of 0 g/kg, 5 g/kg, 20 g/kg, and 100 g/kg, respectively, for 2 months before being exposed to 150 mg/L GA₃. The results revealed that GA₃ exposure decreased significantly all hematological indices (P < 0.05), except leucocytes and mean corpuscular hemoglobin concentration (MCHC), compared to the control group (P > 0.05). GA₃ exposure increased significantly the percentage of nuclear abnormalities, altered erythrocytes and the percentages of tail DNA, compared to the control group (P < 0.05). Spirulina supplementation restored the hematological, poikilocytosis, nuclear abnormalities, and the percentages of tail DNA to near normal levels. The 100 g/kg SP treatment was the most effective in attaining such effect, showing concentration-dependency. The present study reinforces our findings of the toxicity of GA₃ on O. niloticus and suggests that the addition of Spirulina to fish diet can mitigate the hemotoxic effects of GA₃.

Keywords: Comet assay; GA3; Poikilocytosis; Spirulina; Tilapia.

Fig. 1

Representative hematoxylin–eosin-stained blood smears collected from juvenile Nile tilapia (Oreochromis niloticus) showing normal erythrocytes (A), deformed erythrocytes after fish exposure to 150 mg/L gibberellic acid (GA₃) for 15 days (B, C), deformed erythrocytes after fish exposure to 150 mg/L GA₃ for 15 days and feed supplemented with 5 g/kg Spirulina platensis (SP) for 2 months (D), deformed erythrocytes after fish exposure to 150 mg/L GA₃, and 20 g/kg SP diet (E), and deformed erythrocytes after exposure to 150 mg/L GA₃, and 100 g/kg SP diet (F). Tr, tear-drop cell; Cr, crenated cell; Ac, acanthocyte; Eco, eccentric nucleus; Hec, hemolyzed cells; Bin, bionuclei; Loc, loped cell; Eli, elliptocyte; Shc, schistocyte; Kn, kidney cell (1000 × magnification)

Fig. 2

Percentages of head DNA and tail DNA in blood cell comet assays of juvenile Nile tilapia (Oreochromis niloticus). Treatments consisted of exposure to 150 mg/L gibberellic acid (GA₃) and/or diet supplementation with Spirulina platensis (SP) for 2 months prior. Group I, control group; group II, 150 mg/L GA₃; group III, 150 mg/L GA₃ and 5 g/kg SP diet; group IV, 150 mg/L GA₃ and 20 g/kg SP diet; group V, 150 mg/L GA₃ and 100 g/kg SP diet.

Fig. 3

Blood cells stained with ethidium bromide after comet assay from control and treated groups of juvenile Nile tilapia (Oreochromis niloticus). Treatments consisted of exposure to 150 mg/L gibberellic acid (GA₃) and/or diet supplementation with Spirulina platensis (SP) for 2 months prior. A Group I, control group; B group II, 150 mg/L GA₃; C group III, 150 mg/L GA₃ and 5 g/kg SP diet; D group IV, 150 mg/L GA₃ and 20 g/kg SP diet; E group V, 150 mg/L GA₃ and 100 g/kg SP diet. Scale bar 25 μm