Partial fish meal replacement by soy protein concentrate, squid and algal meals in low fish-oil diets containing Schizochytrium limacinum for longfin yellowtail Seriola rivoliana

Highlights

• 80% of fish meal can be replaced by a mix of soybean protein concentrate, squid and algal meals without affecting yellowtail growth.

• Yellowtail intestine integrity was not affected by reduced-fish meal diets supplemented with methionine, lysine, taurine.

• Blends of fish oil, Schizochytrium limacinum meal, and canola oil appear to support acceptable growth in longfin yellowtail.

Abstract

Fish meal (FM) was partially replaced by soy protein concentrate (SPC), squid meal and a defatted algal meal from Haematococcus pluvialis in low-fish oil (FO) diets for longfin yellowtail (Seriola rivoliana). A 50% protein/15% lipid, FM-based diet (FM100) was used as a Control, and four experimental diets were formulated replacing FM with SPC, squid and H. pluvialis meals at levels of 25% (FM75), 40% (FM60), 60% (FM40) and 80% (FM20). Dietary lipid was supplied by blends of FO, a docosahexaenoic acid (DHA)-rich algal meal from Schizochytrium limacinum, and canola oil. With exception of FM100, all diets were supplemented with methionine and lysine. Taurine was supplemented in all diets to achieve a dietary concentration of 1.5%. Diets were fed twice daily for nine weeks to triplicate groups of 20 fish (initial mean weight 2.5 ± 0.1 g) kept in 1000-L circular tanks in a flow-through seawater system. The effects of diet treatment on fish growth, feed utilization, body proximate composition, nutrient retention, fillet fatty composition, and intestinal integrity were evaluated. Growth rate and feed conversion ratio of longfin yellowtail fed the SPC-algal diets were largely comparable to that of fish fed the FM100 diet. Small, but significant differences in nitrogen retention were observed, with fish fed the FM100 diet outperforming those fed the FM 40 and FM 20 diets. Lipid retention was highest in fish fed the FM20 diet and the lowest in the FM75 diet treatment. Fillet fatty acid profile reflected dietary composition and was altered by the level of FM replacement. Lower n − 3 and long-chain polyunsaturated fatty acid (LC-PUFA) levels, higher n − 6 fatty acid levels, and reduced n − 3:n − 6 ratios were associated with increasing FM replacement. Incorporation of the S. limacinum meal partially attenuated dietary and tissue loss of DHA, however, EPA levels declined with increasing FM sparing. No major histological differences or signs of enteritis were observed in any dietary treatments. Results indicate that up to 80% of FM can be replaced by SPC and algal meal, even in low-FO diets, without significantly affecting performance or intestinal integrity of longfin yellowtail.

Statement of relevance

It is shown that FM can be substantially reduced using blends of SPC, squid and algal meals in diets for longfin yellowtail with no significant effect on fish growth and intestinal tissue integrity. The results contribute to the knowledge to improve the sustainability of aquafeeds by using blends of terrestrial and aquatic plant ingredients.

Introduction

Aquaculture production has surpassed capture fisheries as the main source of seafood for human consumption, with farm-raised fish and shellfish production expected to exceed the total fisheries landings within the next ten years (OECD/FAO, 2015). The aquaculture industry is growing and simultaneously becoming more intensive and reliant on industrially compounded aquafeeds (Tacon et al., 2006). As a result, demand for raw materials to produce commercial aquaculture feeds is growing (FAO, 2014) and, in some cases, outpacing growth of the aquaculture industry itself (Tacon and Metian, 2008). Fish meal (FM) and fish oil (FO) obtained from marine forage fish species have been the key protein and lipid sources used in formulated feeds, particularly those made for high value carnivorous marine fish that demand protein-rich, energy-dense diets (Tacon and Metian, 2008, Olsen and Hasan, 2012). Like many other capture fisheries, reduction fisheries landings have been relatively static; though some stocks are predicted to support modest increases in the future, recent observations have indicated declining trends in the global production of FM and FO (Tacon et al., 2011). Complicating the issues of availability are the average prices of FM and FO, which have increased substantially over the past decade (FAO, 2014). Therefore, the sustainable growth of the aquaculture industry is dependent on the availability of alternative sources of protein and lipid. A wide range of ingredients derived from land animals and plants have been tested as alternatives to FM and FO in aquafeeds, and contemporary formulations contain considerably more terrestrial-origin ingredients than those used 10–20 years ago (Tacon et al., 2011). Among these alternatives, soy products have been thoroughly tested as alternative sources of protein, and to a lesser extent, lipid. Despite known limitations related to antinutritional factors that can induce intestinal irritation and damage in some species, soy proteins are widely used in aquafeeds due to their nutritional quality, availability and cost-effectiveness (Gatlin et al., 2007). In contrast, little is known about the value of algal products in formulated diets for carnivorous fish. Defatted or whole cell meals from various species of microalgae, including Spirulina platensis (Nandeesha et al., 1998), Spirulina maxima (Olvera-Novoa et al., 1998), Nannochloropsis sp. and Isochrysis sp. (Walker and Berlinsky, 2011), Tetraselmis sp. (Kiron et al., 2012), Navicula sp. (Patterson and Gatlin, 2013), Desmochloris sp. and Nannofrustulum sp. (García-Ortega et al., 2015) have proven viable protein sources in diets for fish. Other algal products, such as meals from the DHA-rich marine heterotroph Schizochytrium limacinum, have been tested as lipid sources and proven effective in feeds for gilthead seabream (Atalah et al., 2007), cobia (Trushenski et al., 2012), and giant grouper (García-Ortega et al., 2016). Despite these studies, there is a lack of information available regarding the compatibility of terrestrial-origin feedstuffs and algal products used in conjunction to spare FM.

The longfin yellowtail Seriola rivoliana is considered an excellent candidate for intensive marine aquaculture due to its fast growth rate, high flesh quality, and adaptability to intensive culture conditions. The species is found world-wide in subtropical to warm water seas and can reach up to 60 kg in weight (Randall, 2007). S. rivoliana has been commercially farmed in Hawaii and marketed as a sashimi-grade product for more than a decade (Laidley et al., 2004). There is also growing interest in culturing this species in the Mediterranean region (Roo et al., 2014). Yellowtails from the genus Seriola are carnivorous fish reared primarily in net cages and fed either fresh fish or pelleted diets high in FM and FO (Nakada, 2008). Yellowtail culture would benefit greatly from identification of alternative ingredients or ingredient blends that can effectively spare or replace dietary FM and FO. Thus, the aim of this study was to evaluate the use of soy protein concentrate (SPC) and algal meals to partially replace FM in low-FO diets for longfin yellowtail in the context of fish growth, feed utilization, fillet fatty acid composition, and intestinal cell and tissue integrity.