Abstract
Practical diets containing PP sources were elaborated. Increasing levels of di-calcium phosphate were added to diets leading to five different dietary available P levels: 2.5, 3.2, 6.0, 6.5 and 8.0 g kg−1 dry diet. The dietary treatments were tested in 13.5 g Senegalese sole juveniles throughout an 82-day experimental period. Dietary P content had no effect on the productive parameters, while nutrient intake was also similar among dietary treatments, except P intake. Dry matter ADC ranged between 54.9% and 64.0%, and the highest P ADCs value (47.2 ± 0.7%) was achieved in fish fed AP6.0. Dietary phosphorus level significantly influenced body lipid and P compositions. Regression analysis performed on whole-body P and ash contents fitted to quadratic models. Vertebral bone P content was low but increased significantly with increasing dietary P levels. Bone density and deformities occurrence were, however, similar between experimental conditions. An altered status of bone formation–resorption processes in soles fed the lowest P content diet might be inferred from ALP and TRAP activities. In conclusion, overall results state a high tolerance of Senegalese sole to low P content diets and support the utilization of practical diets with high plant protein content.
Highlights
Phosphorus (P) is an essential mineral element in aquafeeds and a major structural constituent of fish skeletal tissues in the form of hydroxyapatite (Lall & Lewis-McCrea 2007)
Other relevant consequences associated with such deficiency conditions are decreased voluntary feed intake (VFI) and body lipid accumulation, as reported in aquaculture produced species as gilthead sea bream (Sparus aurata) (Pimentel-Rodrigues & Oliva-Teles 2001), black sea bream (Sparus macrocephalus) (Shao et al 2008), Japanese sea bass (Lateolabrax japonicus) (Zhang et al 2006), haddock (Melanogrammus aeglefinus) (Roy & Lall 2003), large yellow croaker (Pseudosciaena crocea) (Mai et al 2006) and rainbow trout (Oncorhynchus mykiss) (Rodehutscord et al 1995)
There is limited information concerning flatfish P requirement, but reduced bone mineralization and increased vertebral abnormalities were reported in Atlantic halibut (Hippoglossus hippoglossus) (Lewis-McCrea & Lall 2010), whereas decreased growth was observed in Japanese flounder (Paralichthys olivaceus) (Wang et al 2005) fed dietary total P content below 4–5 g kgÀ1 diet
Summary
71% crude protein (CP), 8% crude fat (CF), EXALMAR, Peru. 2 CPSP 90: 84% CP, 12% CF, Soprope^che, France. 3 Super Prime squid meal: 80% CP, 3.5% CF, Soprope^che, France. 4 Lysamine GP: 78% CP, 8% CF, ROQUETTE, France. 5 VITEN: 85.7% CP, 1.3% CF, ROQUETTE, France. 6 Tubermine GP: 78% CP, 1.5% CF, ROQUETTE, France. 7 Corn gluten feed: 61% CP, 6% CF, COPAM, Portugal. 8 Soycomil P: 65% CP, 0.8% CF, ADM, The Netherlands. 9 Solvent extracted dehulled soybean meal: 47% CP, 2.6% CF, SORGAL SA, Portugal. The vertebral columns (free of soft tissue) of 4 fish per tank were collected and kept at À80 °C until subsequent X-ray analysis for bone density and deformities, determination of vertebrae P content and activity of bone metabolic enzymes. The remaining fish of each treatment were distributed by 2 tanks to determine the ADC of experimental diets using 1% chromic oxide as a dietary inert tracer (Maynard et al 1979). Total P content in feed, whole body and vertebrae samples was determined by spectrophotometry (820 nm) after mineralization and acid digestion, following the molybdateblue/ascorbic acid method (Murphy & Riley 1962). Density of vertebral bone in fish fed the experimental treatments was calculated according to Liu et al (2013), considering the mean grey value as a value of integrated optical intensity (IOD). No significant differences could be observed among dietary treatments (Table 2); AP3.2 and AP8.0 groups pre-
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