End-of-season supplementary feeding in European carp ponds with appropriate plant protein and carbohydrate combinations to ecologically boost productivity: Lupine, rapeseed and, triticale

Abstract

The present study investigated end-of-season (July–September) supplementary feeding strategies for European fishponds (carp farming), which suffer from collapsed natural food base (protein availability). Treatment ponds receiving white lupine ( Lupinus albus ), resulted in higher polyunsaturated fatty acids (PUFA) content (276.1 mg n − 3 PUFA 100 g −1 ) in skinless fillet of Cyprinus carpio than control ponds receiving triticale (179.5 mg n − 3 PUFA 100 g −1 ). Despite lupine being richer in nitrogen (N) and phosphorus (P) than triticale, eutrophication was likely suppressed in treatment ponds. Treatment ponds (∼120 g acid detergent fiber, ADF kg −1 lupine) had higher water transparency and lower water column P than control ponds (∼31 g ADF kg −1 triticale). Surprisingly, triticale (8.5% digestible protein ; low DIAAS LYS 36%) resulted in similar yield (∼1 ton ha −1 ) as lupine (26.5% digestible protein; higher DIAAS LYS 52%, but low DIAAS MET 32%). Therefore, protein quality (methionine) deficiency in lupine was investigated. It was balanced iso‑nitrogenously (38% crude protein) with rapeseed expeller meal ( Brassica napus ): diets T1 (only lupine; Met 0.9% of protein) → T2 (75% lupine: 25% rapeseed; Met 1.2% of protein) → diet T3 (50% lupine: 50% rapeseed; Met 1.4% of protein). A gradual improvement in yield, N and P retention values was observed from T1 to T3 but it did not exceed a low protein (16% crude protein) ‘control’ diet (only triticale; Met 1.9% of protein). Nutrient conversion to fish biomass (protein efficiency ratio and P: N retention ratio) seemed highest in ‘control’ followed by ‘T3’. This could be attributed to starch-mediated protein sparing effect or high organic matter digestibility of triticale (ADC NFE 76%; ADC OM 72%). Which is lacking in either lupine or rapeseed (ADC NFE ≤ 1%; ADC OM ≤ 34%) due to predominance of fibrous carbohydrates (non-starch polysaccharides , NSP). However, in ponds, they may still enhance the food web. In absence of starch, higher ADF influx in pond carp gut may halve absorption of n-3 PUFA from zooplankton. The study concludes end-of-season supplementary feeding with high DIAAS MET, LYS protein combinations (e.g., lupine-rapeseed) and inclusion of starch sources (e.g., triticale) could achieve higher yield and nutrient efficiency in ponds. Most proteinaceous plant feedstuff are rich in NSP or ADF and may contribute to improving pond water quality or food web. Balanced supplementary feeds (e.g., 50% triticale +25% lupine +25% rapeseed expeller), that feed both fish (starch, optimum DIAAS protein ) and pond (NSP, ADF) are suggested.

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