An important area of larval nutrition and feed research is the development of formulated microdiets. Reducing the need for live feeds during the larval phase of culture as well as transitioning larvae onto a well-formulated microdiet have the potential to improve growth and survival rates while reducing overall culture costs. Here we tested two experimental diets versus a commercial control.
Three microdiets were tested on California yellowtail (Seriola dorsalis; CYT) larvae, two experimental diets manufactured by Zeigler, Bros., Inc (Gardners, PA) and one by Otohime (OTO, Marubeni Nisshin Feed, Tokyo, Japan). Treatments were: experimental diet 1 (D1), experimental diet 2 (D2), and OTO. The two experimental microdiets used two different production techniques, D1 was manufactured with standard extrusion practices and D2 was manufactured as a soft-moist extruded pellet. At the start of the study, 16 dph larvae (5 larvae L-1) were stocked into a recirculating system consisting of fifteen 320-L black conical bottom tanks, and the trial duration was 42 days.
Sinking rates were faster for both D1 and D2 diets compared to the OTO, across all particle sizes. Feeding incidence was similar for D1 and OTO at 26 and 30 dph, however at 34 dph the larvae in the OTO treatment had significantly higher feeding incidence than D1 or D2. Standard length (SL) and wet weight (WW) at 59 dph was similar between D1 (SL – 43.2 ± 5.5 mm; WW – 1.56 ± 0.57 g) and OTO (SL – 44.3 ± 5.4 mm; WW – 1.54 ± 0.58 g) and lowest in the D2 treatment (SL – 44.3 ± 5.4 mm; WW – 1.29 ± 0.48 g). Survival at 59 dph was not significantly different between the treatments but was highest in the OTO treatment (30.2 ± 3.8%).
We demonstrated that using the D1 diet to wean CYT can produce similar growth and survival to the commercial control, OTO. OTO is a commonly used weaning diet in the production of many marine finfish species, including Seriola. Even though feeding incidence and survival were not significantly different between the diets, OTO had higher feeding incidence at 26 dph and higher survival. This could be due to the limited size range of the feed particles in the experimental diets and the difference in sinking rates between the experimental and OTO diets. The slower sinking rates for OTO allow for a longer contact time in the water column for the larvae to feed on the diet, and the wider range of feed sizes allows for more of the population to survive through weaning. Continued development of microdiet formulation has the potential to have a significant impact on Seriola culture. Also, having local alternatives to international products, especially diets, is key to the development of a finfish industry in the United States.