New species, processes and products contributing to increased production and improved sustainability in emerging low trophic, and existing low and high trophic aquaculture value chains in the Atlantic

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Domestication of the green seaweed Ulva ohnoi aka `sea lettuce´ for Biofloc effluent bioremediation

Publication . McGovern, Malachy; Mata, Leonardo; Hayashi, Leila

The green macro algae Ulva spp. (Chlorophyta) is being increasingly used in Integrated Multitrophic Aquaculture (IMTA) due to its rapid growth rate and efficiency in the sequestration of excess nutrients. This study tested and evaluated the growth performance of Ulva ohnoi in various concentrations of marine shrimp biofloc effluent (Litopenaeus vannamei). In the first growth experiment, 29mm Ulva discs were cultivated in 1L flasks containing biofloc effluent at 25% [BFT25], 50% [BFT50], 75% [BFT75] and 100% [BFT100] and compared to a seawater control containing 8mL von Stosch standard solution per litre [VS8]. The mean specific growth rates (SGR) after 3 weeks cultivation were [VS8]: 13.14% per day-1 , [BFT25]: 13.63% per day-1, [BFT50]: 14.08% per day-1, [BFT75]: 13.85% per day-1 and [BFT100]: 12.96% per day. From week 3 to week 4, the treatments [BFT25] and [BFT50] showed no growth whilst plants in [BFT75] and [BFT100] treatments continued to grow at a reduced rate of 2.45% per day-1 and 3.35% per day-1 respectively, which was not significantly different from the [VS8] control at 1.71 % per day-1 (p>0.05). The results indicate that the higher nutrient budgets of [BFT75] and [BFT100] continued to support algal growth at higher stocking densities by attenuating the effects of self-shading and stress, demonstrating similar performance to a formulated high-nutrient solution (von Stosch). In the second growth experiment, 19mm discs were cultivated in 1L flasks containing 25% [BF25], 50% [BF50], 75% [BF75] and 100% [BF100] biofloc effluent and compared to a seawater only control [FSW] and a second seawater control containing 10mL von Stosch standard solution per litre [VS10]. During week 1, the [BF75] demonstrated the highest mean specific growth rate (SGRmax) of 25.49 ± 3.23 % per day-1 which was significantly higher that the [FSW] control (p<0.05) and the highest observed growth rate of the study. At the end of the 4 week experiment no significant difference in growth rates was observed between plants in the biofloc treatment groups (p>0.05). During experiment 2, [BF50] reduced levels of TAN by 71.3% in week 1 and by 24.83% in week 2. Nitrite was reduced by 42.73% in week 1 and 28.38% in week 2. Nitrate was reduced by 13.98% in week 1 and 33.3% in week 2. Phosphate was reduced by 13.98% in week 1 and 52.63% in week 2. The results indicate the species’ preference for TAN over nitrate however the study found that sporulation events can release TAN into the medium which has implications for biofilter efficiency and bioremediation. In the sporulation experiment, 5mm Ulva ohnoi discs were excised from a plant acclimatized in FSW enriched with 10mL/L von Stosch (VS10). The discs were placed in petri dishes containing 15 mL of FSW and then subjected to 4⁰C cold shock for [10 mins], [20 min], [1 hour] and [2 hours]. A control treatment was given no cold shock and placed in FSW [FSW control] and a second control was given no cold shock and placed in fresh VS10 medium [VS10 control]. Combined 4°C cold shock [2 hours] and low nutrient shock proved highly effective at inducing a mean rate of sporulation of 90% after 5 days. However, this was not significantly different from low nutrient shock alone (i.e. transfer from VS10 to standard FSW [FSW control]) which caused a mean reproductive output of 76.66% (p>0.05). The results suggest that cold shock treatment is not financially viable however further experiments with plants taken from cultivation in [BF50] or [BF75] are recommended.

2020-12-16Master thesis

Open Access

Mussel meal as a promotor of growth performance for the Whiteleg Shrimp (Litopenaeus vannamei)

Publication . Claessens, Stef; Aragão, Cláudia; Hoffling, Flávia Banderó; Pinheiro, Isabela; Fracalossi, Débora Machado; Vieira, Felipe Nascimento

Mussel meal (species Perna perna) was evaluated as a potential feed additive for whiteleg shrimp (Litopenaeus vannamei) diets to improve growth and cold resistance. Five experimental diets (0, 1, 2, 3 and 4% of mussel meal inclusion) were tested in quadruplicate in whiteleg shrimp, using twenty polyethylene tanks of 400 L. Each tank was stocked with 40 shrimp (3.5 ± 0.5 g), filled with seawater and kept under constant aeration and a temperature of 28.4 ± 0.4 ◦C. After 8 weeks, the growth and feed efficiency of the shrimp were evaluated, and a thermal shock was administered. The shrimp that were fed with the addition of 3 or 4% mussel meal in their diets showed similar results as the control (0% inclusion), while the addition of 1 or 2% mussel meal in the diet resulted in a significantly higher final weight, weight gain and relative growth rate and a lower feed conversion ratio. Further, no differences were observed in thermal shock resistance and survival among the treatments. In conclusion, mussel meal can be used as a feed additive in whiteleg shrimp diets to improve growth, and quadratic regression models indicate that the best levels of inclusion range from 1.73 to 2.00%.

2023-08-25Journal article

Open Access