The shi drum, Umbrina cirrosa, is considered quite promising candidate and emerging alternative Mediterranean aquaculture species to the dominant, European seabass, Dicentrarchus labrax, and gilthead seabream, Sparus aurata, due to its high growth rate and feed efficiency (Segato, Corato, Fasolato, & Andrighetto, 2005). Shi drum feeds mainly on invertebrates and fish (Abellan & Basurco, ), suggesting that this species has high protein requirements. Moreover, the shi drum has a good adaptation capacity to culture conditions and, unlike the winter reproducers seabass and seabream, it is a spring-summer reproducer (Mylonas et al., 2004), thus providing a good species to grow in parallel with the existing cultivated species. Shi drum is a demersal fish, member of the Sciaenidae family (Nelson, Grande, & Wilson, 2016), living on the sandy bottom of maximum 100 m depth, and is distributed all around the Mediterranean Sea area, including the Black Sea. The size of the shi drum during catch is usually around 50-60 cm, but it can reach up to 1 m length and 12 kg weight (Mylonas et al., 2000a). In aquaculture settings, this species can achieve a weight of 500 g in only 15 months, which is near twice the growth rate of seabass and seabream (Fabi & Fiorentini, 1993; Mylonas et al., 2000b), thus making the shi drum a very attractive species for aquaculture. AbstractThe shi drum is an emerging Mediterranean aquaculture species that has gained increasing interest in recent years. However, the nutrient requirements of this species remain to be determined to optimize its culture. The present study evaluated the effects of dietary protein (470g/kg or 520g/kg) to lipid ratios (100g/kg, 150 or 200g/ kg) on the growth performance, nutrient utilization and tissue morphology of the shi drum (7 g average initial weight). Dietary protein levels positively correlated with weight gain, showing high protein demands (>470g/kg) for this species. Nonetheless, dietary lipid levels negatively affected growth rate, feed intake and efficiency, and protein utilization, suggesting that this macronutrient cannot be efficiently utilized in high concentrations (>100g/kg). Histological evaluation revealed fat accumulation within the hepatocytes and the enterocytes with increasing dietary lipid levels, starting from 150g/kg lipid inclusion. Overall, our results confirm the high dietary protein requirements of the shi drum (>470g/kg for fish of 7 g initial weight) and suggest that lipid levels should not exceed 100g/kg of inclusion in the diets as this species has a low tolerance to this macronutrient. K E Y W O R D Sdiversification, emerging aquaculture species, feed utilization, growth performance, histological score, nutrient requirements | 445 KOKOU et al.

Single-cell ingredients (SCI) are considered promising nutrient sources which are produced using environmentally friendly biotechnological processes. The aim of the current study was to evaluate the replacement of fishmeal, plant protein sources, and fish oil with SCI in organic feeds for European sea bass (Dicentrarchus labrax). Bacterial protein, yeast protein, and microalgae were used to replace fishmeal trimmings, soya bean meal, and fish oil from trimmings. Triplicate groups (30 fish per replicate) of European sea bass (14.4 ± 2.4 g) were fed the experimental diets for 71 days. The results showed that the incorporation of SCI at all levels of inclusion significantly enhanced nutrient digestibility. Additionally, growth performance parameters were not affected by SCI inclusion, exhibiting similar or improved values. Moreover, a tendency for improved anterior and posterior gut structure was observed and a significant increase of lysozyme activity at the two highest inclusion levels of SCI was determined. Overall, the results showed that the inclusion of SCI at 15% (bacterial: yeast: algae—9.4: 4.7: 1) is possible without compromising any of the parameters evaluated. According to these findings, a higher substitution of fishmeal trimmings, plant protein sources, and fish oil from trimmings with SCI in organic diets for European sea bass (D. labrax) can be further evaluated in future studies.