Thus far, sustainable production of copepods in captive is still unachievable, possibly due to the use of unsuitable feed, and the cost-effective production protocols are relatively underdeveloped. As a result, wild copepods are still widely used to raise larval fish and invertebrates in commercial hatcheries albeit their poor biosecurity. This study thus aimed to select, culture, manipulate, and engineer local microbiota to create a beneficial microbial consortium for producing bio-secure and high-quality copepods fed with waste-grown microheterotrophs.
A total of 177 indigenous marine isolates comprising bacteria, thraustochytrid protists, and yeasts had been screened for probiotic properties, bioremediation capabilities, and alternative feeds for copepods. Of which, Bacillus subtilis and Alteromonas macleodii were effective in mitigating a magnitude of Vibrio species, notably V. harveyi and V. parahaemolyticus. Interestingly, B. subtilis had better adaptation to a multitude of temperature, salinity, and pH ranges, i.e., 28°C-80°C, 5ppt-35ppt, and pH 3-11, respectively than that of A. macleodii. Among the selected microheterotrophs tested for bioremediation assays, Qipengyuania flava was highly efficient in remediating high-nutrient aquaculture wastewater. The immobilisation of Q. flava cells in beads had further improved their efficiency in wastewater treatment.
Irrespective of brewery wastewater (BW) or food wastewater (FW)-based microbial feeds, the marine cyclopoid copepod, Oithona sp. thrived well when they were fed with Aurantiochytrium sp. as compared to B. subtilis, Rhodotorula mucilaginosa, Tetraselmis sp., only autoclaved wastewater, and no feed. In addition, the inclusion of immobilised bacterial beads did not impair the growth and reproduction of Oithona. Regardless of bead treatments, copepods fed with FW-grown Aurantiochytrium registered 1.5 times greater population densities than those fed with BW-grown Aurantiochytrium albeit BW-grown Aurantiochytrium contained significantly higher protein (43.2%) and polyunsaturated fatty acids (PUFA: 31.35% of total fatty acids) (p<0.05) than FW-grown Aurantiochytrium (protein: 24.0%; PUFA: 7.14%). Irrespective of feeds, Vibrio counts in the Oithona cultures containing immobilised B. subtilis beads were significantly lower (p<0.05) than Oithona cultures with immobilised Q. flava beads or empty beads (without bacteria).
The inclusion of both B. subtilis and Q. flava beads in Oithona cultures fed with FW-grown Aurantiochytrium not only improved water quality, but also significantly reduced Vibrio loads (p<0.05) as compared to Oithona cultures containing either beads of B. subtilis or Q. flava. Nonetheless, copepod populations in all the bead treatments were not significantly different (p>0.05). In conclusion, this study has clearly demonstrated that sustainable production of bio-secure copepods fed with waste-grown microheterotrophs could be achieved through precise microbiome engineering.