Use of seaweed Ulva lactuca for water bioremediation and as feed additive for white shrimp Litopenaeus vannamei

Introduction

In the last decades, aquaculture has been one of the fastest growing industries of food production. By 2015, farmed shrimp represented an estimate global production of 4.8 million metric tons, with a value of US$24.96 billion (FAO, 2017). Some of the challenges for this growing activity are the reduction of coastal water pollution impact (Herbeck et al., 2013) and the search for non-conventional ingredients to produce high quality feeds (Little, Newton & Beveridge, 2016). In the case of seaweeds produced by aquaculture, it has been estimated by 2015 a worldwide production of 28.5 million metric tons valued in US$4.46 billion (FAO, 2017). For Ulva lactuca seaweed, research interest has increased due to their rapid vegetative growth in the presence of high nutrient levels and has been adapted to culture in tanks (DeBusk, Blakeslee & Ryther, 1986), with various industrial applications including human and animal nutrition (Ortiz et al., 2006; Yaich et al., 2011).

The use of seaweeds in integrated multi-trophic aquaculture (IMTA) has been proposed as an alternative for environmental-sustainable expansion of aquaculture, serving as primary food source and also for water bioremediation due to their high capability of removing inorganic nutrients from wastewater (Neori et al., 2004; Neori, 2008; Fleurence et al., 2012). Benefits of integrated aquaculture of shrimp and green seaweeds has been documented for Ulva clathrata that showed high efficiency in removing the inorganic nutrients from water effluents (Copertino, Tormena & Seeliger, 2009), in addition as an improvement of feed utilization in white shrimp Litopenaeus vannamei (Cruz-Suárez et al., 2010) and in brown shrimp Farfantepenaeus californiensis (Peña Rodríguez et al., 2016; Peña Rodríguez et al., 2017). U. lactuca improved water quality when cultured with western king prawn Penaeus latisulcatus (Van Khoi & Fotedar, 2011) and with L. vannamei (Brito et al., 2014); Caulerpa sertularioides presence resulted in F. californiensis growth enhancement (Portillo-Clark et al., 2012).

Seaweeds are an excellent source of protein, carotenoids, minerals, polysaccharides, and vitamins making their utilization as feed additives attractive (Kumar et al., 2011; Peña Rodríguez et al., 2011; Syad, Shunmugiah & Kasi, 2013). Some seaweeds have been suggested as a partial feed substitute (Marinho-Soriano et al., 2007) for shrimp diet, and considered a good source of protein (Da Silva & Barbosa, 2009), which represents the most expensive fraction of feed cost. In some cases, shrimp composition is modified when fed seaweeds, these changes may include lipid content and carotenoids (Cruz-Suárez et al., 2010; Subhra Bikash, 2015), or total cholesterol (Casas-Valdez et al., 2006). The optimal level of inclusion of seaweed meal in shrimp feed varies among seaweed species, but, in most cases, studies have found benefits when included not higher than 5% (Cruz-Suárez et al., 2009; Rodríguez-González et al., 2014; Cárdenas et al., 2015; Yu et al., 2016; Schleder et al., 2017).

Despite some studies explore the use seaweeds for water bioremediation, there is no reports of the use of U. lactuca produced under these conditions as a feed ingredient for shrimp. The aim of the present work was to evaluate shrimp growth and water quality of an integrated culture system with U. lactuca and, on the other side, the effect of U. lactuca meal as feed additive at different inclusion levels on shrimp performance, lipid and carotenoid content.

Materials and Methods

Results

At the end of feeding trial 1, shrimp under daily clean water exchange (CWE) and daily seaweed U. lactuca water exchange (SWE) treatments resulted in significant higher (p < 0.05) final weight, weight gain, and SGR compared to shrimp with no water exchange (NWE) (Table 2). Feed consumption was similar among the treatments, nevertheless FCR observed in NWE treatment was significantly higher than the rest of the treatments (p < 0.05). Shrimp under NWE treatment showed a lower percentage of survival but not significantly different compared to the rest of treatments. At the end of the experimental period, water quality parameters were significantly different among treatments (Fig. 1). The NWE treatment resulted in significant increment (p < 0.05) of total ammonia nitrogen, nitrites, nitrates, and phosphate compared to treatments with water exchange, whereas the pH showed no significant differences among treatments. Removal of inorganic compounds in U. lactuca treated water was higher than 80% for nitrogenous compounds and 64% for phosphate compared to the treatment without water exchange. Total harvest of fresh U. lactuca, under the experimental conditions, was 225 ± 25 g per tank, with a specific growth rate of 5.37 ± 0.41 (% day⁻¹). After drying, U. lactuca meal resulted in a 15.5% of crude protein and 36.5% ash (Table 1), which was used to prepare experimental feeds for feeding trial 2.

In feeding trial 2, experimental feeds did no show differences in proximal composition except for ash content in feed containing 3% of U. lactuca meal (3UL), which resulted 1.1% higher compared to the control feed (0UL) as expected. Total carotenoids in U. lactuca meal resulted in 3.5 mg g⁻¹ in dry basis. Results of shrimp performance after evaluation of experimental feeds with different inclusion levels of U. lactuca meal (Table 3) showed that shrimp fed diet with 3% U. lactuca meal had a significantly higher growth in terms of final weight, weight gain, and SGR (p < 0.05) compared to the control diet (0UL) and that of 1% of U. lactuca (1UL). Shrimp fed 2UL treatment showed no significant differences in growth parameters compared to the other treatments. In terms of feed utilization, the 3UL diet induced a significantly lower (p < 0.05) FCR compared to the rest of the treatments. Shrimp survival was higher than 95% in all treatments. Total lipid content in whole shrimp (Fig. 2A) was significantly higher in shrimp with 3UL compared to the rest of treatments (p < 0.05). Additionally, shrimp fed 3UL showed significantly higher concentration of total carotenoids in the head; in the muscle, 2UL and 3UL yielded significantly higher amounts of carotenoids than the rest of treatments; and considering the whole shrimp, all U. lactuca meal diets resulted in significantly higher content of carotenoids compared to the control diet (Fig. 2B). Lineal regression model showed a correlation between level of U. lactuca meal inclusion in feed and total carotenoids in whole shrimp (y = 3.605x + 17.22, R² = 0.88) and head (y = 5.738x + 28.518, R² = 0.788). Water quality parameters during the second experimental period were very stable among treatments: temperature (28 ± 0.4 °C) pH (8.0 ± 0.1), NH3, NH4+ (<0.5 mg L⁻¹), NO₂ (<0.25 mg L⁻¹), and NO₃ (<5 mg L⁻¹).

Discussion

According to the water quality parameters during experiment 1, results revealed the high efficiency of U. lactuca in removing nitrogen compounds and phosphorus from shrimp’s wastewater (80% and 64%, respectively) under the integrated recirculation system. These results are consistent with other reports describing the high efficiency of Ulvales in biofiltering inorganic compounds from aquaculture effluents. Copertino, Tormena & Seeliger (2009) determined that U. clathrata removes up to 70–82% of the total ammonia nitrogen (TAN) and 50% of phosphate. In a study of an intensive co-culture system of U. lactuca and L. vannamei, TAN and phosphate were significantly reduced in culture water by 25.9% and 24.6%, respectively, compared to a system without U. lactuca (Brito et al., 2014). The nitrogenous compounds removed by seaweed reflected 15.5% protein content in meal, which revealed a higher proportion than reports in wild collected U. lactuca (7.1 to 10.7%) (Wong & Cheung, 2000; Yaich et al., 2011; Tabarsa et al., 2012), but lower than described for U. lactuca cultured in a controlled system (21.1%) (Ventura & Castañón, 1998). An integration of a total or partial recirculating system of U. lactuca and shrimp may decrease the need of out coming water, improving farm biosecurity and reducing the possibility of disease outbreaks (Muniesa et al., 2015). According to the present experimental results, U. lactuca meets different criteria suggested by other authors to select an efficient seaweed biofilter for integrated aquaculture, which includes nutrient intake from wastewater (Kang, Park & Chung, 2011), seaweed density, and water flow rate (Al-Hafedh, Alam & Buschmann, 2015).

Water bioremediation with U. lactuca (trial 1) did not affect shrimp growth or feed utilization, as described by Fourooghifard et al. (2017), where the water quality improved without affecting shrimp growth in a zero water exchange system of integrated culture of L. vannamei and Gracilaria cortica. No significant growth differences were observed in L.  vannamei cultured in floating cages with red seaweed Kappaphycus alvarezii compared to shrimp monoculture system (Lombardi et al., 2006). On the other hand, when no water exchange was performed, shrimp growth and feed utilization was affected possibly by water quality. It has been described that exposure to high concentrations of ammonia in water increases oxygen and energy demand in shrimp (Racotta & Hernández-Herrera, 2000) reflected in lower growth (Chen & Kou, 1992). However, shrimp performance in low or no water exchange culture systems can also be affected by the shrimp stock densities (Hopkins et al., 1993), feed composition (Wasielesky et al., 2006), and feeding frequency (Tacon et al., 2002).

In feeding trial 2, where U. lactuca produced by bioremediation was evaluated as feed ingredient, shrimp growth was improved when fed 3% U. lactuca meal in feed. Rodríguez-González et al. (2014) suggest that the limiting inclusion level for U. lactuca meal in shrimp feed should not exceed 5%, showing that levels of 10 and 15% reduced significantly shrimp growth compared to a control diet without U. lactuca inclusion. Serrano Jr, Santizo & Tumbokon (2015) also experimented with 15 and 30% U. lactuca meal inclusion in P. monodon shrimp, finding no growth improvement at the lower inclusion level and significant reduction of shrimp growth at the higher inclusion level. Similar results in fish were observed, poor growth and feed utilization were shown in African catfish (Abdel-warith, Younis & Al-asgah, 2016) and in Rainbow trout (Yildirim et al., 2009) when high levels of U. lactuca meal (>20% and 10% respectively) were included in feed compared with 0% inclusion, suggesting lower inclusion levels.

Shrimp growth improvement at low inclusion levels were found with other seaweed meals, as for example with 2 or 4% of Macrocystis pyrifera (Cruz-Suárez et al., 2000) or Sargassum sp. (Suárez-García, 2006) included in shrimp feed. Yu et al. (2016) also recommends low inclusion levels (2 or 3%) of Gracilaria lemaneiformis meal in order to improve weight gain in L. vannamei. The growth promotor effect, as in the present work, is generally attributed to vitamins, minerals and lipids present in the seaweed (Cruz-suárez et al., 2008; Tabarsa et al., 2012).

U. lactuca showed high content of ash (36.5%) similar to the value reported by Rodríguez-González et al. (2014) (41.7%), which could explain the limiting inclusion level of seaweed meal in the feed. High inclusion levels of seaweed meal in feed reflects higher contents of ash, which has been related with decrement of feed digestibility (Brunson, Romaire & Reigh, 1997; Yang et al., 2009). In a study in black tiger shrimp Penaeus monodon, apparent digestibility of U. lactuca meal was significantly lower (71%) than for protein concentrate from U. lactuca (99%) (Santizo, Serrano & Corre, 2014). This decrement of feed digestibility on Ulva meal diets is not observed when fresh seaweed is used as food, like when shrimp are fed fresh U. lactuca (Pallaoro, do Nascimento Vieira & Hayashi, 2016) or U. clathrata (Cruz-Suárez et al., 2010), which, in both cases, could be save at around 50% of pelleted feed without negative effects on shrimp growth.

The increase of 30% in whole shrimp lipid content of shrimps fed 3% U. lactuca meal diet, respect to control feed, was also described in L. vannamei co-cultured with U. clathrata, where a combination of pelleted feed and seaweed increased up to 50% total lipid content in shrimp (Cruz-Suárez et al., 2010). This increase in shrimp lipid content could be partially attributed to carotenoids content in the algae. Carotenoid in crustaceans are responsible for pigmentation and as source of provitamin A and as antioxidants (Liñan Cabello, Paniagua-Michel & Hopkins, 2002). Total carotenoids in the U. lactuca meal in the present study was in the range described for the same species and others Ulvales (240 to 500 ug g⁻¹ fresh weight) (Xia, Li & Zou, 2004; Kumar et al., 2010; Peña Rodríguez et al., 2011). Shrimp fed diets with U. lactuca meal significantly increased whole shrimp carotenoid content, with the highest concentration in the head. Penaeid shrimp effectively use carotenoids from Ulvales to increase body pigmentation. Shrimp fed fresh U. clathrata increase carotenoid content as the use of pelleted food decreased (Cruz-Suárez et al., 2010). In another study, feeds with 3.3% of seaweed (U. clathrata) meal inclusion diet resulted in higher shrimp pigmentation after cooking respect to Ascophilllum nodosum and Macrocystis pyrifera diets (Cruz-Suárez et al., 2009). A diet containing 5% of Enteromorpha intestinalis meal increased significantly the astaxanthin content in P. monodon muscle compared to a control diet after 30 days of feeding trial (Subhra Bikash, 2015).

Conclusions

In conclusion, the results of the present study demonstrated that U. lactuca can be used on integrated aquaculture systems in terms of nitrogen and phosphate water bioremediation, and the inclusion of the seaweed biomass produced as feed additive improves shrimp growth performance and shrimp carotenoid content.

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