Introduction
Fishmeal (FM) is a cornerstone of aquafeed, but its sustainability and cost challenges necessitate the search for alternative protein sources. Black soldier fly larvae (BSFL, Hermetia illucens) meal has emerged as a promising substitute due to its high protein content and efficiency in converting organic waste into valuable biomass. However, its high fat content, particularly saturated lauric acid, and the presence of chitin can negatively impact nutrient digestibility and growth performance in fish. Recent studies highlight that the nutritional quality of insect larvae, especially their fatty acid profile, can be improved by altering their diet during rearing. Spirulina, a microalga rich in protein, vitamins, minerals, and essential fatty acids, is known to enhance the nutritional value of insect meals for aquaculture. Given that BSFL can bioaccumulate fatty acids from their growth substrate, enriching their diet with spirulina can significantly improve their nutritional value for aquaculture. This study aimed to investigate the effects of replacing fishmeal with conventional BSFL meal and spirulina-enriched BSFL meal on the growth performance, whole-body proximate composition, and plasma biochemical parameters of juvenile Asian seabass (Lates calcarifer). While previous research on various fish species has shown mixed results regarding insect meal inclusion, our study represents the first comprehensive investigation into the combined effects of BSFL meal and spirulina enrichment on Asian seabass. The findings highlight that 25% replacement with spirulina-enriched BSFL (+BSFSP25%) provides optimal growth performance while higher inclusion levels (50%) may have negative effects on growth and biochemical indices.
Methodology
The 56-day feeding trial was conducted using 300 juvenile Asian seabass with an average initial weight of approximately 8.6–8.7 g. The fish were randomly distributed into five experimental groups with three replicates each, housed in 300-liter tanks. All tanks were supplied with filtered saltwater and continuous aeration. Water quality parameters, including temperature (28–30°C), dissolved oxygen (5–7 mg/L), pH (7.5–8), and salinity (45 g/L), were monitored daily. Fish were fed to apparent satiation twice per day with five experimental diets: a control diet (FM) containing 100% fishmeal, and four diets where fishmeal was replaced by black soldier fly larvae meal (BSF) at 25% (BSF25%) and 50% (BSF50%) levels, and by spirulina-enriched BSFL meal at 25% (+BSFSP25%) and 50% (+BSFSP50%) levels. All diets were formulated to be isoproteic (~40% crude protein) and isolipidic (~9% crude lipid). At the end of the trial, samples were collected to measure growth performance indices, whole-body proximate composition, and plasma biochemical parameters. Growth performance was assessed using Final Body Weight (FBW), Weight Gain (WG), Specific Growth Rate (SGR), Feed Conversion Ratio (FCR), and Survival Rate (SR). Whole-body proximate analysis determined the content of protein, lipid, moisture, and ash. Blood samples from two fish per tank were used for plasma analysis of total protein, glucose, cholesterol, and triglycerides. All data were analyzed using one-way ANOVA followed by Duncan's test at p < 0.05.
Results
Dietary treatments significantly influenced the growth performance and feed utilization efficiency of the fish (p<0.05). The most pronounced growth outcomes, including final body weight (FBW; 57.4 ± 0.1 g), weight gain (WG; 572.7 ± 0.1%), and specific growth rate (SGR; 3.4 ± 0.0% day⁻¹), were achieved in the +BSFSP25% group. Conversely, the lowest growth metrics were observed in the BSF50% and +BSFSP50% cohorts, both of which exhibited a significant decline compared to the other treatments. While the BSF50% group recorded the highest feed conversion ratio (FCR), this difference remained statistically non-significant. Notably, the survival rate was markedly compromised in the BSF50% treatment compared to all other experimental groups. Proximate composition analysis of the whole body revealed that crude protein levels peaked in the BSF25% and BSF50% treatment groups. In contrast, the highest crude lipid content was recorded in the +BSFSP50% group. A significant reduction in moisture content was observed in the BSF50% and +BSFSP50% cohorts (p<0.05). Furthermore, ash content reached its maximum level in the +BSFSP50% group, whereas the control (FM) group exhibited the lowest ash values. Dietary treatments exerted a statistically significant influence on the plasma biochemical profiles of the fish (p<0.05). Total protein concentrations were markedly elevated in the BSF25% and BSF50% cohorts compared to the other experimental groups. Regarding glucose metabolism, the highest values were recorded in the +BSFSP50% group, while the BSF25% treatment yielded the lowest levels. Furthermore, a clear trend was observed in the lipid profiles, with cholesterol and triglyceride concentrations peaking in the +BSFSP50% and +BSFSP25% groups, respectively. Conversely, the most reduced cholesterol levels were found in the BSF50% group, whereas the BSF25% group exhibited the lowest triglyceride concentrations.
Discussion
The outcomes of the present study are congruent with prior research, highlighting that the partial substitution of fishmeal with black soldier fly larvae (BSFL) meal, especially when enriched with Spirulina platensis, exerts a substantial influence on the growth performance, carcass composition, and physiological status of Asian seabass. The superior growth metrics observed in the +BSFSP25% cohort underscore the efficacy of this hybrid dietary strategy. This synergistic improvement may be attributed to the well-balanced amino acid and fatty acid profiles of BSFL meal, augmented by the diverse bioactive compounds and potent antioxidative properties of spirulina. Such a nutritional combination likely optimizes metabolic pathways and enhances nutrient assimilation, thereby promoting superior growth. In conclusion, these findings suggest that integrating spirulina-enriched insect meal at a 25% replacement level offers a sustainable and high-performance alternative to conventional fishmeal in Asian seabass aquaculture. Conversely, the growth retardation observed at the 50% substitution level highlights that high dietary inclusion of BSFL meal may exceed the physiological tolerance of Asian seabass. This decline is potentially attributable to the presence of anti-nutritional factors (ANFs), specifically chitin, alongside an imbalanced essential amino acid profile. These findings corroborate that the optimal replacement threshold for fishmeal in this species remains below the 50% mark. Furthermore, the concomitant increase in carcass adiposity and hyperlipidemia observed in the +BSFSP50% group suggests a significant metabolic perturbation, necessitating a more precise calibration of the dietary lipid matrix in high-inclusion formulations.
Conclusion
In summary, this research offers a viable and sustainable framework for modern aquaculture. The strategic substitution of 25% of fishmeal with spirulina-enriched BSFL meal not only bolsters growth performance and optimizes carcass quality but also enhances the overall physiological resilience of Asian seabass. This dietary intervention represents a significant advancement in the development of eco-friendly and cost-effective aquafeeds, effectively mitigating the industry’s heavy reliance on finite marine-derived proteins. Ultimately, these findings facilitate the transition toward more circular and resource-efficient production systems, promoting the long-term sustainability of the global aquaculture sector.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgment
The authors would like to thank the South of Iran Aquaculture Research Centre for providing the experimental facilities and technical support throughout the study.