Abstract
Algae, or “greenwater,” is a traditional water additive used in finfish aquaculture, but is associated with high costs and potentially harmful bacterial growth. “Claywater,” a mix of clay and seawater, has been explored as a replacement for greenwater. In some fish species, however, claywater reduces survival rates, but the mechanisms are not understood. A link between water additive and microbial community composition may exist. In this study, the effects of different water additives on the microbial communities of larval sablefish were studied. Three treatments were evaluated: a traditional greenwater additive, a claywater additive, and a greenwater additive switched to claywater after one week. Microbial communities were characterized using 16S rRNA gene sequencing, and sablefish survival and growth were recorded. Tank seawater microbial communities were significantly influenced by water additive (treatment). Sablefish microbiomes were significantly, but weakly influenced by treatment, and there were time-specific differences within the claywater treatment. Sablefish from the treatment that was switched after one week maintained microbiomes that were more similar to the initial greenwater treatment. In general, sablefish were dominated by Vibrionaceae OTUs. Variability in the sablefish microbiomes between tanks from the same treatment was high, especially in the claywater treatment, which may have confounded treatment effects. Larvae in the claywater treatment had significantly lower survival rates compared to greenwater and greenwater-claywater treatments, but no treatment effect was observed on sablefish growth (length). Overall, results suggest that claywater does not negatively impact survival or the microbial community of sablefish when preceded by one week of greenwater.
Highlights
In aquaculture, most marine fish species require water additives, such as algae, to increase turbidity so larvae can feed successfully (Boehlert and Morgan, 1985; Utne-Palm, 2002; Carton, 2005)
After 1 week (14 March), cell counts from all treatments were significantly higher than the start date of the experiment (β = 0.474, SE = 0.017, z = 28.05, p < 0.001). This increase was especially evident in the GG seawater, where cell counts were 2.6 times higher on the final date (22 Mar) compared to the initial date (7 Mar) of the experiment (β = 0.582, SE = 0.208, z = 2.80, p < 0.01). The results of this experiment demonstrated that water additives result in different larval survival rates and microbial community compositions in sablefish rearing tanks
Our results indicate that intra-specific differences were not attributable to parental cross, further implicating the yolk sac and diet as factors in the microbial community structure of the larvae
Summary
Most marine fish species require water additives, such as algae, to increase turbidity so larvae can feed successfully (Boehlert and Morgan, 1985; Utne-Palm, 2002; Carton, 2005). Water with this type of additive is known as “greenwater,” and while effective, it is costly and contributes to excess organic material in tanks and subsequent bacterial proliferation, including pathogens (Attramadal et al, 2012). As DMSP degradation is microbially mediated, there may be a link between fish survival, water additives, and the microbial communities in larval sablefish and the surrounding seawater
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