Finding alternatives to the conventional protein sources such as fish meal and soy meal is crucial to sustain the growth of aquaculture sector in future. While evaluating the alternatives to the conventional protein sources, the impact of the novel feed ingredients on the waste load in the system is often neglected. As the production systems are moving indoors and stricter regulations are enforced on the nutrient discharge limits from the aquaculture systems, it becomes prudent to investigate the effect of novel dietary ingredients on the load of solid and accumulation of organic matter and nutrients. High abundance of fecal suspended solids will have negative impact on the functioning of biofilters as at high COD/N load the efficiency of nitrifying reactors is reduced. This may result in buildup of nitrogenous metabolites in the system over time.  The experiment planned will look at the interactions between feed-fish and fecal axis in a recirculating aquaculture in response to diet with varying fecal characteristics. Results from previous studies indicated that two diets similar in nutrient composition but differing in ingredients resulted in feces which differed significantly in size distribution, stability, recovery and chemical composition. These variations in fecal characteristics can have significant impact on the functioning of the system as feces of small size accumulate in the system over time and are also subjected to further breakdown by the mechanical forces of the system or undergo biological degradation mediated by bacteria. Particles of smaller size also have higher nutrient leaching potential and also offer larger surface area to volume ratio for attachment and multiplication of heterotrophic bacteria. The bacterial activity in the system will also depend on the total solid load and the nature (biodegradability potential) of carbohydrate fraction accumulating in the system as non-recovered feces. In order to test the effect of fecal quality on performance of the system, diets will be fed to the animals restrictively at predetermined fixed rate. The variation in the solid load on the system and other nutrients is expected to arise primarily from fecal quality (impacting recovery) and digestibility of diets. Since the diets selected is expected to have no major variation in DM digestibility, the differences in fecal solid load on the system will be primarily reflective of the variation in the fecal characteristics. Therefore, the current experiment is planned to study the impact of differences in the fecal characteristics on COD load, nutrient load and bacterial activity of the system along with the impact on the growth performance of the fish .

Aim of the experiment- Growth performance of the fish, COD and BOD load of the system, Bacterial activity in the system, Suspended solid load, turbidity and particle size distribution,  COD, Nitrogen and Phosphorus mass balances.

Role of the student- Feeding fish, Determination of water quality parameters, Lab work for estimation of nutrients, Particle size measurement.

Experimental fish- Rainbow trout

Experimental duration- 8 weeks

Type of experiment- Non-invasive trial

Experimental system- 6 Individual RAS with two diets in triplicate