White sea bream (Diplodus sargus) and brown meagre (Sciaena umbra) were caught from the wild in Aegean Sea (Greece), and studied for their proximate, fatty acid and amino acid composition to evaluate their nutritional value for human consumption and their potential as candidate fish species for Mediterranean aquaculture diversification. Both species exhibited very low muscle fat, ranging at 1%. White sea bream was found to have higher muscle eicosapentaenoic (EPA) and docohexaenoic (DHA) contents and total n-3 fatty acids than brown meagre. A superiority of white sea bream in aspects of thrombogenicity was indicated, showing higher atherogenic (0.679) and thrombogenic indices (0.377) comparing to the respective values for brown meagre (0.610 and 0.579). The two-studied species exhibited high-quality protein as food source, with white sea bream showing a higher essential to non-essential amino acid (EAA/NEAA) rate, 0.764 vs 0.704, respectively. The individual to total essential amino acids rates of lysine and leucine were the highest ones for both studied species, while no significant differences were observed among them.

The potential use of plant protein (PP) blends (soybean, wheat, rapeseed, corn gluten and wheat gluten) in the diet of juvenile meagre (Argyrosomus regius) was investigated at increasing levels to replace fishmeal (FM) (33% and 56%) in six isonitrogenous (480 g/kg) and isoenergetic (22 MJ/kg) diets, which were supplemented with crystalline lysine. Meagre juveniles (36 ± 0.6 g initial weight) were reared in triplicate for 60 days at 19.4 ± 2.4°C to evaluate their growth performance, feed utilization parameters, body proximate composition and the prevalence of systemic noninfectious granulomatosis. Results indicated that there was no significant difference (GLM ANOVA, p > 0.05) in growth performance and feed utilization parameters in meagre fed the diet containing 300 g/kg FM (33% FM replacement) compared to the control group (450 g/kg FM inclusion), although a trend showing inferior body gain and feed conversion ratio was observed. However, higher levels of FM replacement (56%) by PP blends (200 g/kg FM inclusion) significantly impaired growth performance, feed conversion and protein efficiency rates (p < 0.05), which may be linked to a decrease in feed intake and/or reduced levels of bioactive compounds or other micronutrients present in FM. On the other hand, increasing dietary lysine levels from 25 to 29 g/kg in the diets containing the same PP content and 200 g/kg inclusion of FM significantly improved growth performance in juvenile meagre. The replacement of FM did not affect lipidosomatic and hepatosomatic indexes in any of the experimental groups evaluated (p > 0.05). The aetiology of granulomatosis found in different tissues was not due to the presence of bacteria, as no bacterial structures were detected in histological slides when samples were stained with the Gram, Ziehl‐Neelsen and Fite‐Faraco staining. The presence of chronic systemic noninfectious granulomatosis was observed in meagre from all the experimental groups regardless the level of FM replacement by PP blends, indicating that the onset and progression of granulomatosis occurred insidiously at earlier life stages of meagre and persisted at variable levels thereafter. The liver and kidney were found to be the most severely affected tissues.

Callinectes sapidus is native to the Atlantic coasts of the Americas. In the Mediterranean, it appeared around 1949 and though that it is established in East Mediterranean waters, relevant studies are limited. The aim of the present study is to report quantitative and qualitative data on the blue crab’s biology and ecology in its non-native range, that are indispensable for management purposes. Papapouli Lagoon is in Thermaikos Gulf and is ecologically impacted by the blue crabs. Fyke nets with a 20 mm mesh opening were soaked for 12 to 14 h during each survey. Abiotic environmental parameters were obtained. The length–weight relationships were expressed by the equation W = aLb. The species’ ecological preferences at Papapouli Lagoon were assessed with PERMANOVA analysis, using the abiotic parameters as factors. Student’s t-tests were used to assess the differences between sexes. The sex ratio of the blue crab’s population was assessed by a Chi-square (χ2) analysis. The sex ratio was found to be 1.28:1, in favour of males. The most dominant group size of male blue crabs was the 61–70 mm of CL and 130–139 mm of CW. Also, the dominant size group of female blue crabs was 60–69 mm of CL and 120–129 mm CW. The maximum abundance of blue crabs was recorded at a salinity range from 24‰ to 25‰ and the water temperature range was from 26 to 28 °C.

As the demand for fish food increases globally, there is a need for the aquaculture industry to expand its farmed fish species base in order to increase productivity and sustainability. To unlock a species potential for aquaculture, the nutrient requirement of the fish in terms of protein, amino acids, lipids, minerals and vitamins must be well understood to ensure efficient nutrient utilization and rapid growth. The new development in aquafeed production has witnessed commercial fish feed industries incorporating large quantities of plant-based ingredient in fish feed formulation (Lee et al., 2020). However, the main constraint when alternative proteins of plant origin are used in the fish diets is the limiting content in some essential amino acids (EAA), mainly lysine and methionine. Lysine is