CIRCULAR FEED INGREDIENTS AND ENHANCEMENT OF NUTRIENT DIGESTIBILITY IN Cyprinus carpio POND AQUACULTURE
Introduction
Common carp ( Cyprinus carpio ) contributed 8.6% (4.2 million tonnes, live weight) to total inland finfish aquaculture in 2020, ranking it fourth after grass carp, silver carp, and Nile tilapia
. More than 90% of common carp production from Europe comes from Russian Federation, Poland, the Czech Republic, Ukraine, Hungary, Belarus, Serbia, Germany and France
. In European carp fishponds, three different diet scenarios exist: an abundance of zooplankton compared to cereals in April-May, a balanced amount of zooplankton and cereals in June-July, and a deficiency of zooplankton compared to cereals in August-September. Experimental simulations of the 3 dietary scenarios demonstrated that when the carp’s diet consisted of either a low or high amount of zooplankton , it resulted in nutritional imbalances and high digestive and metabolic losses (nitrogen (N) and phosphorus (P)) compared to scenarios where the diet was somewhat balanced
.
This research is therefore, aimed at evaluating locally available feed ingredients (circular) through digestibility trials. This will serve as the basis for selecting the best (highly digestible) ingredients for formulating balanced and cost-effective diets for C. carpio in ponds. Additionally, more circular feed ingredients in aquafeeds means more phytates in aquafeeds. Therefore , pond-associated microbes were also isolated and evaluated for their ability to hydrolyse phytate and other nutrients.
Results
Digestibility
The apparent digestibility coefficient of protein (nitrogen) (ADC-N) , phosphorus (ADC-P), nitrogen free extracts (NFE+fibre), and energy of the 12 ingredients (circular) are present ed in Table 1. The ADC-N of all ingredients tested were above ~75 % except for malt sprout waste and pea, whereas ADC-P of all ingredients were above 25 % except for lupine sprout, rapeseed expeller, and sunflower expeller.
Characteristics of the isolates
Nineteen (19) out of the 25 isolates had the ability to hydrolyze a t least one of the substrates. All the four substrates were hydrolyzed by 11 isolates with HG1 showing the highest hydrolysis (Figure 2).
Discussion
Aside from lupine and pea, all the ingredients investigated in this study are ‘waste’ from local bakery, brewery, oilseed processing, and other industries. This study shows the potential of valorising waste into fish meat and lipid for humans. I ngredients such as noodles-pasta, unsold bread, sugar beet discards, and extruded morning cereals (EMC-discards) have high protein sparing potential with low N and P content (data not shown), thus are best suited for beginning-of-season diets to spare zooplankton (reduced grazing pressure from carp as a result of satiation). The other ingredients are best for formulating complete balanced diets for the end-of-season (when zooplankton are depleted)
.
Plant feed ingredients are high in phytate-P but fish are unable to digest phytate-P effectively
. Isolates such as PW2 especially is best suited for the external hydrolyses of phytate in feed ingredients. Other potential isolates for bioprocessing of feed ingredients include HG1, FG1, FG 3, FG5, PW1, PW3, PW4, PW5, PW6. Further safety studies are however, recommended.