Publication Date



Open access

Embargo Period


Degree Type


Degree Name

Master of Science (MS)


Marine Affairs and Policy (Marine)

Date of Defense


First Committee Member

Daniel D. Benetti

Second Committee Member

Jorge A. Suarez

Third Committee Member

Gavin J. Partridge


Microbial management in the culture of marine pelagic fish is crucial for the refinement of larval rearing protocols and strategies. Standard larval rearing methods employ the addition of live or paste microalgae to culture environments, termed “green water” culture, which promotes the growth of undesired opportunistic bacteria associated with microbial “pioneer” communities. A non-selective approach for the reduction in bacteria by substituting microalgae paste with a non-organic clay additive was evaluated for two marine pelagic fish, cobia (Rachycentron canadum) and yellowtail kingfish (YTK; Seriola lalandi). Both trials induced turbidity using Old Mine #4 Kentucky ball clay and Reed Rotigrow Nannochloropsis algae paste set to similar Secchi disc depths (55 – 65 cm). In addition to paste and clay additives an experimental artificial algae (solgel) was used in the YTK trial. Final growth (mm), survival (%), and total Vibrio communities (CFU ml-1) were measured in both trials. Moreover, in the YTK trial, total bacteria levels and submerged (downwards and upwards facing) light intensities were assessed between treatments. Results were evaluated using independent t-tests for the cobia trial and one-way ANOVAs with Tukey HSD post-hoc tests for the YTK trial. No significant differences were found in growth (P = 0.40) and survival (P = 0.54) between treatments in the cobia trial. Significant differences were seen in total Vibrio counts at day 7 and 10 (P < 0.05) between treatments. Although differences in total Vibrio were found, the bacterial population in the algae paste tanks did not have a negative impact on the larvae’s growth or survival. The cobia trial results indicate that clay may successfully function as an algae paste substitute without any detrimental effect. The response of YTK trial to clay was very different to that of cobia. Both clay and solgel had a negative impact on YTK larvae’s growth, survival, SBI, FI, and prey consumption (P < 0.05). Differences were seen at 5 DPH for total bacteria and total Vibrio (P < 0.05) between treatments. Submerged upwards facing light intensity in clay was significantly greater than the algae paste and artificial algae treatments (P < 0.0001). Immediate disorientation and stress in yolksac YTK at initiation of the clay turbidity treatment was present. It was hypothesized that light scatter on clay particles and back-scatter from tank color may have caused the negative impacts seen on the larvae. This study warrants more research regarding interactions between light intensities, tank color, tank dimensions, and the use of non-organic algae substitutes.


cobia, yellowtail, Seriola, clay, bacteria, algae