Exploring the nutritional potential of Monoraphidium littorale and enriched copepods as first feeds for rearing Nile tilapia (Oreochromis niloticus) larvae

One of the challenges in the aquaculture industry is providing nutritionally balanced and environmentally sustainable live food for fish larvae. Therefore, the rearing techniques of fish larvae with preferred starter food should be given importance for obtaining optimal hatchery production. Nile tilapia, Oreochromis niloticus larvae just after yolk absorption (body length 0.950 ± 0.004 mm; body weight 6.00 ± 0.02 mg) were reared in laboratory conditions for 16 days, feeding with 6 different diets to know their effect on survival and growth. The diets were live Monoraphidium littorale (T1), live enriched copepods with M. littorale (T2), powdered M. littorale (T3), powdered enriched copepods (T4), live M. littorale + live enriched copepods (T5), and powdered M. littorale + powdered enriched copepods (T6). The proximate composition, amino acid profile and fatty acid content of both M. littorale and copepods were analyzed. The biochemical analysis of the dried powder of enriched copepods and M. littorale revealed that both of them are excellent sources of protein, amino acids, and lipids, especially with monounsaturated and polyunsaturated fatty acids. The O. niloticus larvae fed the T2 diet exhibited the most favourable outcomes, with significantly higher larval gain in weight and percent weight gain, in comparison to the larvae fed other diets (p < 0.001 for all comparisons). The LG% and SGR of the larvae were also significantly higher in T2 in comparison to the T1, T3, T4, and T6 (p < 0.001 for all comparisons) except T5. In addition, the highest percent survival rate of the larvae was observed in T2 (95 %) followed by T4 (93 %), T6 (93 %), T3 (82 %), T5 (73 %) and then T1 (43 %). Based on the present findings, it is recommended that live copepods enriched with M. littorale can be utilized as a starter food for the rearing of Nile tilapia, O. niloticus larvae in hatcheries because of its enriched nutritional profile.

Whey permeate as a phosphorus source for algal cultivation

Microalgal cultivation for biodiesel and feed requires recycled nutrient resources for a sustainable long-term operation. Whey permeate (WP) from dairy processing contains high organic load (lactose, oils, and proteins) and nitrogen (resources tested for microalgal cultivation) and organic phosphorus (P) that has not yet been tested as a P source for microalgal cultivation. We explored the potential of green algae strains (brackish) and polyculture (freshwater) in exploiting P from WP added to a medium based on either seawater (7 psu) or landfill leachate. Both strains showed a capacity of using organic P in WP with equal growth rates (0.94-1.12 d^-1 ) compared with chemical phosphate treatments (0.88-1.07 d^-1 ). The polyculture had comparable growth rate (0.25-0.57 d^-1 ) and biomass yield (152.1-357.5 mg L^-1 ) and similar or higher nutrient removal rate in the leachate-WP medium (1.3-6.4 mg L^-1  day^-1 nitrogen, 0.2-1.1 mg L^-1  day^-1 P) compared with the leachate-chemical phosphate medium (1.2-4.7 mg L^-1  day^-1 nitrogen, 0.3-1.4 mg L^-1  day^-1 P). This study showed that WP is a suitable P source for microalgal cultivation over a range of salinities. To date, this is the first study demonstrating that raw WP can replace mineral P fertilizer for algal cultivation. PRACTITIONERS POINTS: Whey permeate is a comparable phosphorus source to standard fertilizers used in algal cultivation. Green algae removed phosphorus effectively from whey permeate. Microalgal cultivation is a good approach for treatment of whey permeate in combination with a nitrogen-rich wastewater.