IMTA Lab - Brazil

Federal University of Rio Grande (FURG) have been working in biofloc systems as a sustainable and biosecure alternative to intensive culture systems which rely on expensive filtration systems (RAS) or high-water exchange rates (flow-through systems). The biofloc is composed of uneaten feed, feces, secretions, and their associated algal, bacterial, and microplankton communities. So, this biofloc provides the substrate for microbial nitrification of toxic ammonia to nitrate, in the same production tank, and eliminates the necessity for external treatment or water exchange, improving economic and environmental sustainability. In addition to providing water quality, biofloc particles can be consumed directly by culture species such as shrimp, tilapia and oysters, thereby making more efficient use of the nutrients contained within the feed and subsequently lowering total feed costs. 

The majority of multi-trophic systems combine one or more fed species (high-value carnivores or omnivores) with one or more extractive feeders (bivalves and/or seaweed) that can utilize suspension particles or dissolved nutrients to grow. So, the production of shrimp in high density, as a target species, with tilapia and oyster, as organic matter (biofloc) consumers, and seaweed, as a nutrient consumer, can result in reduced feed costs and minimal or zero waste generation.   

In an inland closed IMTA system proposed by FURG lab, zero-emission of effluents is possible, since the cycling of organic matter and nutrients occurs in the same production units. The shrimp are fed daily, generating waste in the form of uneaten feed and excretion. These residues will enhance the growth of the biofloc, which will be consumed by tilapia and oysters and the nutrients will be consumed by the seaweed. 

Screenshot 2021-09-01 at 12.04.24.png

During the first year FURG developed 3 experiments:

  • Experiment 1 - Nutrient consumption by seaweed (Ulva linza; U. fasciata; U. flexuosa) in different biomass (0.5kg and 1kg/m3)

Screenshot 2021-09-01 at 12.05.24.png

  • Experiment 2 – Biofloc consumption by tilapia in different densities (35 and 70 ind/m3)

Screenshot 2021-09-01 at 12.05.27.png

  •  Experiment 3 – Biofloc consumption by Oysters (C. gigas- left and C. gasar-right) 

Screenshot 2021-09-01 at 12.17.00.png

The results are interesting and indicate that in this system with bioflocs it is possible to integrate some species.

The main results observed were: 

  • Shrimp had excellent performance, even with densities of 450 ind/m2, growing 1.3g per week and with FCR 1.2. The final weight was 14g

  • Tilapia grew between 11 and 13g per week at salinity 18 and had an FCR 0.7

  • The oyster Crassostrea gasar (native to Brazil) had better survival in the biofloc system, possibly because it was adapted to higher temperatures (28 to 30°C) and turbidity. Growth was reduced and it will be necessary to find a new form to control the bioflocs concentration in the system. 

  • Among the different algae species tested, Ulva fasciata showed better performance in the system, especially when kept in the first 5 cm of depth. The luminosity is greatly reduced from 10 cm onwards and algae growth is compromised. 

Figure 1. Water with biofloc Figure 2. Shrimp produced in the system(Author: Luis Poersch, Associate Professor at the Federal University of Rio Grande)

Figure 1. Water with biofloc Figure 2. Shrimp produced in the system

(Author: Luis Poersch, Associate Professor at the Federal University of Rio Grande)