ÔØ Å ÒÙ× Ö ÔØPlease cite this article as: Abbink, Wout, Blanco Garcia, Ainhoa, Roques, Jonathan A.C., Partridge, Gavin J., Kloet, Kees, Schneider, Oliver, The effect of temperature and pH on the growth and physiological response of juvenile yellowtail kingfish Seriola lalandi in recirculating aquaculture systems, Aquaculture (2011), doi: 10.1016/j.aquaculture.2011.11.043 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 AbstractA search for a viable new fish species for culture in recirculating aquaculture systems (RAS) in the Netherlands identified yellowtail kingfish Seriola lalandi as having excellent potential.To assist in determining the most appropriate water quality conditions for this species in RAS, the effect of water temperature (21, 23.5, 25, 26.5 and 29 ˚C) and pH (6.58, 7.16 and 7.85) were tested in two separate experiments. Growth performance, feed conversion, stressphysiological and metabolic parameters were assessed in juvenile yellowtail kingfish grown in pilot-scale RAS. Growth was optimised at a water temperature of 26.5 °C, in combination with maximum food intake and optimum food conversion ratio (FCR). Increasing temperature from 21 °C to 26.5 °C resulted in a 54 % increase in the fish's final weight after 30 days. A water pH of 6.58 resulted in mortality and inhibited both growth and FCR due to physiological disruptions to which the fish could not adapt.

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The effects of salinity on plasma osmolality, branchial chloride cell density, feed consumption and conversion and growth performance of yellowtail kingfish (Seriola lalandi) were evaluated. Fish (11.6 ± 0.6 g) were kept for 29 days at 14, 18, 22, 26 (experimental) and 30 g L−1 (control) salinity in independent, pilot‐scale recirculation aquaculture systems. No differences in plasma osmolality or chloride cell numbers in gills were observed, pointing to a strong osmoregulatory capacity in the juveniles. Fish at 14, 18 and 22 g L−1 (7.61 ± 0.19, 7.61 ± 0.01 and 7.61 ± 0.13% day−1, respectively) had higher growth rates than fish at 26 and 30 g L−1 (7.10 ± 0.05 and 6.97 ± 0.06% day−1 respectively). The higher growth rate at lower salinity resulted from increased feed intake; feed conversion was not different. An evaluation of the impact of salinity on growth rate of on‐growing stages (till market size) seems warranted to assess whether the profitable effects of low salinity persist in later stages of this important aquaculture species.

Two mass mortality events (MMEs) of marine mussels that took place in the Oosterschelde, the Netherlands—the first in 2015/2016 and the second in 2019—both severely affected mussel production. The current study presents our observations on the onset and course of both MMEs and discusses probable putative causes. The two MMEs displayed a distinct course of events. The first event started in November 2015 with high mortality rates on culture plots, which remained elevated until the autumn of 2016. Approximately 40–50% of mussels from all age classes were lost on culture plots and 100% were lost from wild seed beds. The second event started in April–May 2019 and continued until the end of July, with mortality ranging from 20 to 100%, again from all age classes. Culture areas other than the Oosterschelde and other shellfish species were not affected. Histological and bacteriological screening produced no evidence for common pathogens or pollution as a primary mortality factor and there is no indication of abnormal environmental conditions preceding or during the events. We hypothesize that a cumulation of stressors results in weakening of the mussels and in elevated mortality rates. In 2019, this cumulation of stressors could be high spawning activities (an unusual high concentration of mussel larvae was found in April) that resulted in very low condition from April to June, a Phaeocystis bloom in April to May that prevented a quick recovery, and the development of granulocytomas that were found in up to 60 to 70% of live mussels as a consequence of cumulative stress. Although no (single) putative causes could be identified, this study contributes to the knowledge on MMEs in mussels and fits in a wider and disturbing trend on mortality events in shellfish.

Seaweeds may represent immuno-stimulants that could be used as health-promoting fish feed components. This study was performed to gain insights into the immunomodulatory effects of dietary seaweeds in Atlantic salmon. Specifically tested were 10% inclusion levels of Laminaria digitata (SW1) and a commercial blend of seaweeds (Oceanfeed®) (SW2) against a fishmeal based control diet (FMC). Differences between groups were assessed in growth, feed conversion ratio and blood parameters hematocrit and hemoglobin. After a LPS challenge of fish representing each of the three groups, RNAseq was performed on the head kidney as major immune organ to determine transcriptomic differences in response to the immune activation. Atlantic salmon fed with dietary seaweeds did not show major differences in performance in comparison with fishmeal fed fish. RNAseq resulted in ∼154 million reads which were mapped against a NCBI Salmo salar reference and against a de novo assembled S. salar reference for analyses of expression of immune genes and ontology of immune processes among the 87,600 cDNA contigs. The dietary seaweeds provoked a more efficient immune response which involved more efficient identification of the infection site, and processing and presentation of antigens. More specifically, chemotaxis and the chemokine-mediated signaling were improved and therewith the defense response to Gram-positive bacterium reduced. Specific Laminaria digitata effects included reduction of the interferon-gamma-mediated signaling. Highly upregulated and specific for this diet was the expression of major histocompatibility complex class I-related gene protein. The commercial blend of seaweeds caused more differential expression than Laminaria digitata and improved immune processes such as receptor-mediated endocytosis and cell adhesion, and increased the expression of genes involved in response to lipopolysaccharide and inflammatory response. Particularly, expression of many important immune receptors was up-regulated illustrating increased responsiveness. NF-kappa-B inhibitor alpha is an important gene that marked the difference between both seaweed diets as Laminaria digitata inhibits the expression for this cytokine while the blend of seaweeds stimulates it. It can be concluded that the inclusion of seaweeds such as Laminaria digitata can have important modulatory effects on the immune capacity of Atlantic salmon resulting in a more efficient immune response.

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By introducing recirculation aquaculture systems (RAS) in the nursery phase of the blue mussel (Mytilus edulis) (17–18 mm), we aimed at a similar growth and survival and a similar water quality compared to the commonly used flow‐through systems (FTS). To calculate water flow and size of the biofilter, a series of experiments were done to determine clearance rate (9.26 mL min−1), pseudo faeces threshold (60 000 cells Pavlova lutheri mL−1), nitrogen production (0.00065 mg TAN h−1 ind−1 and 1.6 × 10−5 mg NO2–N h−1 ind−1) and oxygen consumption (0.03 ± 0.01 mg O2 h−1 ind−1). RAS showed no significant differences in water quality (0.06 mg TAN L−1; 7.7 mg O2 L−1) and growth performance of mussel seed specific growth rate (SGR = 5% day−1) after the experimental period of 4 weeks compared with FTS. The low water refreshment, 10% per day, as well as the constant chlorophyll concentrations (9.76 ± 1.06 μg L−1), suggests the potential of RAS as culture system for mussel seed.