Introduction
The integrated multitrophic system emerges as a more sustainable alternative to traditional biofloc systems. The purpose of integrating shrimp and fish is to ensure that the fish can consume excess of bioflocs and use the microbial protein for their growth. The present study aimed to evaluate the performance of Litopenaeus
vannamei shrimp and Nile tilapia Oreochromis niloticus in an integrated multitrophic culture with a biofloc system approaching the heterotrophic and chemoautotrophic pathways.
Methodology
The experiment was carried out at the Marine Aquaculture Center, Institute of Oceanography, Federal University of Rio Grande – FURG/ Brazil, for 75 days. Each system consisted of a 17 m 3 tank where the shrimp were allocated (400 shrimp/m2), a 4 m3 tank where the tilapia were allocated (45 fish/m3) and 1 m3 were introduced 3 kg of Ulva
lactuca. These tanks were interconnected and the water circulated between them by submerged pump and the water returned by gravity. There are two treatments: Chemoautotrophic and Heterotrophic, with three replications each. Shrimp had an initial weight of approximately 1g and tilapia 25g.
In the chemoautotrophic treatment was fertilized with inorganic compounds, the system water was matured to stimulate the development of nitrifying bacteria (Ferreira et al., 2021). In the heterotrophic treatment, ammonia was controlled by fertilization with organic carbon (sugarcane molasses) after storage of the animals, when the concentration reached 1.0 mg/L or. The animals were fed twice a day (8:00 am and 4:00 pm), the tilapia were underfed with 1% of the tank biomass to stimulate the consumption of bioflocs (Poli et al., 2019).
Results
The mean values of temperature, dissolved oxygen, pH, alkalinity, total suspended solids (TSS) and settling solids (SS) were equal between treatments. The mean values of nitrite (Figure 2) and ammonia were higher in the heterotrophic treatment. The mean values of nitrate and phosphate were higher in the chemoautotrophic treatment, as well as the clarification time (Table 1). The zootechnical performance of shrimp was better in the chemoautotrophic treatment. Only FCR and survival showed no significant difference between treatments. There was no significant difference in any of the zootechnical parameters for the fish.
The results regarding algae are being processed and could not be incorporated until now.
Discussion
For maturation of the chemoautotrophic system, inorganic fertilizations with ammonium chloride and sodium nitrite were performed for 52 days, with the objective of maturing the nitrite-oxidizing bacteria in the system, before the animals were stored. The objective of the predominantly chemoautotrophic system is for the ammonia excreted by the animals to be converted into nitrate through nitrification. When compared to the predominantly heterotrophic system, which converts ammonia into microbial biomass, this process generates about 40x less total suspended solids (Ebeling et al., 2006). The previous inorganic fertilization in the chemoautotrophic treatment was efficient to keep the levels of nitrite low and this reflected in the better zootechnical performance of the shrimps. With higher biomass, consequently, the feed supply was higher in the system, reflecting higher TSS concentrations. It was not possible to identify a significant difference in the consumption of TSS by the fish, but the FCR lower than 1 in the heterotrophic treatment, without statistically differing from the chemoautotrophic treatment, indicates that the animals used the bioflocs as a food supplement. The chemoautotrophic system showed better shrimp productivity, but the tilapia performance was better in the heterotrophic treatment.
Acknowledgements
This work was developed as part of the ASTRAL (All Atlantic Ocean Sustainable, Profitable and Resilient Aquaculture) project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 863034.
References
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