Received: 26 January 2018 | Revised: 28 June 2018 | Accepted: 7 July 2018 DOI: 10.1111/are.13792 ORIGINAL ARTICLE Dietary krill meal inclusion contributes to better growth performance of gilthead seabream juveniles Reda Saleh1,2 | Lena Burri3 | Tibiabin Benitez‐Santana3 | Serhat Turkmen1 | Pedro Castro1 | Marisol Izquierdo1 1Aquaculture Research Group (GIA), Institute of Sustainable Aquaculture and Abstract Marine Ecosystems (ECOAQUA), There is a need to find sustainable alternatives to fishmeal (FM) and fish oil (FO) in Universidad de Las Palmas de Gran Canaria, Telde, Spain feed formulations to support the continued growth of aquaculture. FM is mostly 2Oceanography Department, Faculty of produced from mass‐caught pelagic species, but the production has been relatively Science, Alexandria University, Alexandria, constant for several decades. The aim of this study was to investigate the potential Egypt 3Aker BioMarine Antarctic AS, Lysaker, of dietary krill meal (KM) inclusion as a sustainable alternative to FM. In view of Norway that, a feeding trial with gilthead seabream juveniles was conducted to evaluate Correspondence whether dietary KM at 3%, 6% and 9% inclusion improves growth performance in Lena Burri, Aker BioMarine Antarctic AS, comparison with a control diet. At the end of the study, fish in the 9% KM group Oksenøyveien 10, NO‐13327 Lysaker, Norway. showed significantly higher body weight (32.76 g) compared with fish fed the con- Email: [email protected] trol diet (30.30 g). Moreover, FM replacement by 9% KM indicated a reduction in the accumulation of lipid droplets in the hepatocytes and around the pancreatic islets. In summary, this study suggests that FM can be reduced in diets for seab- ream without negatively affecting growth performance, when KM is added. On the contrary, KM enhances gilthead seabream growth and reduces lipid accumulation and damage of hepatocytes, which will open an interesting innovation line to com- pletely replace FM by alternative terrestrial protein sources and the partial inclusion of KM. KEYWORDS fishmeal replacement, growth performance, krill meal, seabream juvenile 1 | INTRODUCTION are required for the further expansion of aquaculture. FM can be partially replaced in the diets of many fish species, but in most cases, Fishmeal (FM) and fish oil (FO) used to be the principal ingredients high or complete replacements have detrimental effects mainly due in formulated marine species and salmon feeds, but high prices and to imbalanced amino acids and the presence of toxins or antinutri- sustainability concerns have stimulated the search for novel feed tional factors. Another key factor is lower feed intake (FI) of fish, ingredients. In 2008, the aquaculture industry used 68% and 88% of because of decreased diet palatability or acceptability as the level of the world’s production of FM and FO respectively (Tacon & Metian, alternative protein sources increases, especially plant proteins 2008). The availabilities of FM and FO for feed inclusion are (Chatzifotis, Polemitou, Divanach, & Antonopoulou, 2008; Kissil, decreasing or at best stagnating (Food of Agriculture Organization of Lupatsch, Higgs, & Hardy, 2000; Kubitza, Lovshin, & Lovell, 1997). United Nations [FAO], 2016). However, an increase in the size of Considerable progress has been made in replacing FM with a variety the global aquaculture industry and the fact that FM production is of plant protein ingredients such as soybeans, lupins, peas and limited have resulted in raising prices, as high as $2,000 per ton. canola (Gatlin et al., 2007; Torrecillas et al., 2015, 2017 ). Almost Therefore, alternative sources of protein and lipids derived from fish | Aquaculture Research. 2018;1–7. wileyonlinelibrary.com/journal/are © 2018 John Wiley & Sons Ltd 1 2 | SALEH ET AL. complete replacement can be achieved by a balanced supplementa- promote the reduced use of FM and FO in commercial feed for the tion of specific micronutrients and feed attractants (Torrecillas et al., further sustainable development of aquaculture. 2017). Such an attractant is Antarctic krill (Euphausia superba), with a high protein content, favourable amino acid and fatty acid profiles, 2 | MATERIALS AND METHODS as well as enhanced palatability properties. It was suggested that the low molecular weight soluble compounds of krill meal (KM), such as 2.1 | Feeding trial nucleotides, amino acids and high levels of trimethylamine N‐oxide, all act together to make KM an effective attractant and flavouring Gilthead seabream juveniles were obtained from the hatchery at the agent (Ogle & Beaugz, 1991; Shimizu, Ibrahim, Tokoro, & Shirakawa, GIA facilities (Grupo de Investigación en Acuicultura, Las Palmas de 1990). This has been confirmed in various species, such as seabream Gran Canaria, Spain), where the experiment was carried out. A feed- (Pagrus major; Shimizu et al., 1990) and largemouth bass (Micropterus ing trial was conducted testing 9% dietary KM versus a control diet salmoides; Kubitza & Lovshin, 1997). In addition, freeze‐dried krill, for fingerlings with an initial body weight of 12.71 ± 0.11 g and ini- including the soluble protein fraction, stimulated feeding activity of tial fork length of 8.7 ± 0.10 cm. Triplicate groups of fingerlings juvenile Atlantic cod (Gadus morhua) and Atlantic halibut (Hippoglos- were randomly distributed in six experimental tanks (at a density of sus hippoglossus), which resulted in increased growth performance 55 fish tank−1) and were fed manually one of the experimental diets and nutrient utilization (Tibbetts, Olsen, & Lall, 2010). Olsen et al. until visual apparent satiety, three times a day, for 12 weeks. FI was (2006) concluded that KM could fully replace FM in diets to Atlantic calculated by recording diet uptake every day, as well as uneaten salmon (Salmo salar) without negatively affecting growth, feed utiliza- pellets at each feeding point. tion and fish health. Salmon fed diets, where 20% or 40% of the FM All tanks (500‐L fibreglass cylinder tanks with conical bottom and was replaced with KM, had a better specific growth rate (SGR) com- painted with light grey colour) were installed in an open system and pared with the FM group. Similarly, no growth reduction was appar- were supplied with filtered sea water (34 ppm salinity) at an increas- ent when rainbow trout (Oncorhynchus mykiss) were fed a diet with ing rate of 100% h−1 along the feeding trial to ensure good water total FM replacement and the addition of deshelled KM (Yoshitomi, quality. Water was continuously aerated attaining 6.7 ± 0.54 mg/Lto Aoki, & Oshima, 2007; Yoshitomi, Aoki, Oshima, & Kazuhiko, 2006). assure good water quality during the entire trial. Water quality was Moreover, Suontama et al. (2007) described no negative effects on tested daily, and no deterioration was observed. Average water tem- Atlantic salmon reared in sea water, when fed diets where FM was perature along the trial was 19.6 ± 1.0°C, and a natural photoperiod replaced with up to 60% Northern krill (Thysanoessa inermis), 40% was adopted. Antarctic krill or 40% Arctic amphipod (Themisto libellula) respec- Two isoproteic and isolipidic experimental diets (pellet size of 2 tively. The authors found that the Atlantic salmon fed a diet, where and 3.2 mm) were formulated containing different KM levels: 0% 40% of the FM was replaced with Antarctic KM, obtained better (control group) and 3%, 6% and 9% KM (QrillTM Aqua; Aker BioMar- SGR than fish fed a control diet. In red porgy (Pagrus pagrus), FM ine Antarctic AS, Norway) (Table 1). The proximate analysis and fatty substitution by KM had no negative effect on growth or feed utiliza- acid composition of the experimental diets are listed in Table 2. tion (Izquierdo, Kalinovski, Thongrod, & Robaina, 2005). In addition, At the beginning and end of the trial, all fish were weighed and because of its content in esterified astaxanthin, KM gave a natural the fork length was measured. Before sampling, fish were always reddish skin coloration to red porgy, in contrast to the lower pig- submitted to 24 hr of fasting. Biological parameters of the growth mentation of fish fed purified canthaxanthin. In another study, the performance of fish were calculated, namely SGR, FI and feed con- inclusion of krill oil high in phospholipids (PL) in larval seabream diets version ratio (FCR). In addition, the hepatosomatic index (HSI) was improved fish growth and survival more effectively than soybean determined. Samples were kept at −80°C until the analysis of bio- PL. It enhanced omega‐3 polyunsaturated fatty acids (n‐3 PUFA) and chemical composition. particularly eicosapentaenoic acid (EPA) incorporation into larval tis- sues and upregulated the gene expression of bone development 2.2 | Biochemical analysis biomarkers as well as bone mineralization (Izquierdo et al., 2016). Moreover, an increase in dietary krill oil up to 120 g/kg improved Prior to biochemical analysis, samples of 5 fish per tank (in total 15 seabream larval digestive functioning, growth and survival (Saleh fish per treatment) were homogenized (T25 Digital Ultra‐Turrax; et al., 2013). Some environmental NGOs have expressed concerns IKA®, Germany) and analysed in triplicate. Moisture (A.O.A.C., 1995), over the use of KM, which is considered to be essential to all crude protein (A.O.A.C., 1995) and crude lipid (Folch, Lees, & Stan- trophic marine food webs. However, recently the International ley, 1957) contents of fish and diets were analysed. Fatty acid Union for Conservation of Nature has recommended the inclusion methyl esters (FAMES) were obtained by transmethylation of crude of certified krill to reduce the use of FM and FO to produce more lipids as described by Christie (1982). FAMES were separated by sustainable aquafeeds, particularly in larval or broodstock condition- gas‐liquid chromatography (GLC) under the conditions described by ing diets. Izquierdo, Watanabe, Takeuchi, Arakawa, and Kitajima (1990), quan- The objective of this study was to determine the potential bene- tified by a flame ionization detector (FID, Finnigan Focus SG; ficial effects of KM inclusion in feed for juvenile seabream and to Thermo Electron Corporation, Milan, Italy) and identified by SALEH ET AL.