Ecological stoichiometry and nutrient reduction strategies for sustainable but intensive hybrid pond systems – concepts for regenerative aquaculture

Using fish-free pond-water mesocosms, we examined the response of algal growth to additions of fish feces and carbonaceous material under realistic or challenging dilution scenarios during both dynamic and steady states (Experiments I-II). Using pond living labs observational study, we examined uncertainties in zooplankton body composition under variable bottom-up and top-down pressures, mediated by nutrient stoichiometry and fish stock index (FSI), respectively (Experiment-III). In experiment-I, the objective was to assess graded levels of N and P inputs via fish feces at the expense of organic C on the dynamic and steady states of mesocosms containing pond water. In experiment-II, the objective was to assess the behavior of pond water mesocosms at graded levels of stoichiometric effects from C:P and N:P molar ratios. For this purpose, two isonitrogenous fish feces and two isocarbonaceous feeds were used, with low and high C:P or N:P ratios, respectively. In experiment-III, using temperate carp ponds across the vegetative season as aquatic living labs, the objective was to explore the relative variability of amino acid and fatty acid contents in zooplankton (additionally, body condition factor) under highly variable water nutrient stoichiometries (molar DIN:TP, DOC:DIN, DOC:TP) and fish stock index (FSI). It was done to understand any hidden sensitivities in zooplankton’s nutritional ecology (exerting top-down control on algae) to variable nutrient inputs and predation pressure in its environment.