Does the Gradual Substitution of Fishmeal by Dried Zooplankton in the Diet of Gilthead Seabream Sparus aurata Fries Improve their Growth Performance and Survival Rates?

Finding suitable alternatives to animal protein used in the manufacture of fish feed is one of the major challenges at present since these alternatives must be sustainable, with an abundance in nature, available and easy to obtain, and economically inexpensive. The goal of this study was to investigate how the gradual replacement of fishmeal with dried zooplankton (DZ) affected gilthead seabream (Sparus aurata) larvae over a four-month experiment.  Nine hundred fish were allocated into five groups with an initial average weight of 0.227± 0.030g. The fish were fed five isonitrogenous and isocaloric diets in which fish meal was replaced by dried zooplankton (DZ) at different levels: 0 (G1), 25 (G2), 50 (G3), 75 (G4), and 100% (G5). The effects of diets on growth performance, feed utilization, survival, and body composition were tested. The results showed that substituting dried zooplankton for fishmeal had a strong relationship with fish weight gain, length gain, and feed conversion ratio, with R² values of 0.99, 0.94, and 0.97, respectively. The polynomial regression model, which exhibited the maximum response at G4 and G5, was determined to be the most suitable regression model to reflect the fish's reaction to the replacement of fish meal with dried zooplankton (DZ). Using dried zooplankton (DZ) instead of fish meal (FM) in the early stages of gilthead seabream feeding proved to be an excellent strategy for enhancing growth and reducing mortality rates by 50%.  The 75% replacement rate showed the best results in terms of lowering mortality, while both the 75 and 100% replacement rates were optimal for growth criteria. In summary, this study found that a complete substitution of fish meal with dry zooplankton meal in gilthead seabream diets was achievable without adverse impacts on weight development, length growth, or feed utilization.