PerformFISH

Aquaculture of European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) is an essential activity in the Mediterranean basin. Several EU Horizon 2020 and regional projects are focusing on the improvement of their farming performance. This workshop aimed at displaying, sharing and discussing projects' achievements among interested colleagues engaged to work with fish diseases. The most innovative research outputs aiming to improve the European mariculture were presented during this workshop, including updates from EU Horizon 2020 projects MedAID, PerformFISH, ParaFishControl, FutureEUAqua and the Italy-Croatia Interreg project AdriAquaNet.

The phenotype of juvenile fish is closely associated with the adult phenotype, thus consisting an important quality trait for reared fish stocks. In this study, we estimated the correlation between the juvenile and adult body-shape in Gilthead seabream, and examined the genetic basis of the ontogenetic trajectories. The body shape of 959 pit-tagged fish was periodically examined during the juvenile-to-adult period. Individual shape ontogenetic trajectories were studied in respect to the initial (juvenile) and final (adult) phenotypes, as well as to the rate that adult phenotype is attained (phenotypic integration rate). We found that the juvenile body-shape presented a rapid change up to 192.7 ± 1.9 mm standard length, followed by a phenotypically stable period (plateau). Depending on the shape component considered, body-shape correlations between juvenile and adult stages ranged from 0.22 to 0.76. Heritability estimates (h ² ) of the final phenotype ranged from 0.370 ± 0.077 to 0.511 ± 0.089, whereas h ² for the phenotypic integration rate was 0.173 ± 0.062. To our knowledge, this is the first study demonstrating that the variance of the ontogenetic trajectories has a substantial additive genetic component. Results are discussed in respect to their potential use in selective breeding programs of Gilthead seabream.

Haemal lordosis, V-shape bending of the haemal vertebrae, is a frequent abnormality of reared fish. Lordosis severity ranges from light deformations of vertebral axis, with insignificant effects on external morphology, to severe axis deformations with significant impact on body-shape. In the present study, we developed a simple morphometric index (PrAn) that links lordosis severity at the juvenile stage with fish body-shape at harvesting, without requiring to radiograph or sacrifice the samples. Examined seabream specimens were part of our previous study (Fragkoulis et al. 2019, Sci. Rep. 9, 9832), which monitored the effects of lordosis on the external morphology of pit-tagged seabream juveniles during their growth, up to harvest size. At both juvenile and adult stages, PrAn was effective in discriminating the normal fish from ca the 70% of lordotic fish. Our results suggest the PrAn as a valuable scale of quality, which quantifies the lordosis effects on fish external morphology, both at the juvenile stage and at harvest. Depending on the lordosis rates, and the hatchery strategy on the maximum allowed abnormality rates, this scale can cull out different rates of lordotic fish, without affecting the fish with normal phenotype or the lordotic fish with high recovery potential.

Temperatures experienced during early ontogeny significantly influence fish phenotypes, with clear consequences for the wild and reared stocks. We examined the effect of temperature (17, 20, or 23 °C) during the short embryonic and yolk-sac larval period, on the swimming performance and skeleton of metamorphosing Gilthead seabream larvae. In the following ontogenetic period, all fish were subjected to common temperature (20 °C). The critical swimming speed of metamorphosing larvae was significantly decreased from 9.7 ± 0.6 TL/s (total length per second) at 17 °C developmental temperature (DT) to 8.7 ± 0.6 and 8.8 ± 0.7 TL/s at 20 and 23 °C DT respectively (p < 0.05). Swimming performance was significantly correlated with fish body shape (p < 0.05). Compared with the rest groups, fish of 17 °C DT presented a slender body shape, longer caudal peduncle, terminal mouth and ventrally transposed pectoral fins. Moreover, DT significantly affected the relative depth of heart ventricle (VD/TL, p < 0.05), which was comparatively increased at 17 °C DT. Finally, the incidence of caudal-fin abnormalities significantly decreased (p < 0.05) with the increase of DT. To our knowledge, this is the first evidence for the significant effect of DT during the short embryonic and yolk-sac larval period on the swimming performance of the later stages.

Haemal lordosis, V-shape bending of the haemal vertebrae, is a frequent abnormality of reared fish. Lordosis severity ranges from light deformations of vertebral axis, with insignificant effects on external morphology, to severe axis deformations with significant impact on body-shape. In the present study, we developed a simple morphometric index (PrAn) that links lordosis severity at the juvenile stage with fish body-shape at harvesting, without requiring to radiograph or sacrifice the samples. Examined seabream specimens were part of our previous study (Fragkoulis et al. 2019, Sci. Rep. 9, 9832), which monitored the effects of lordosis on the external morphology of pit-tagged seabream juveniles during their growth, up to harvest size. At both juvenile and adult stages, PrAn was effective in discriminating the normal fish from ca the 70% of lordotic fish. Our results suggest the PrAn as a valuable scale of quality, which quantifies the lordosis effects on fish external morphology, both at the juvenile stage and at harvest. Depending on the lordosis rates, and the hatchery strategy on the maximum allowed abnormality rates, this scale can cull out different rates of lordotic fish, without affecting the fish with normal phenotype or the lordotic fish with high recovery potential.

Haemal lordosis is a frequent abnormality of the vertebral column. It has been recorded to develop in different finfish species, during the hatchery rearing phase. Under certain conditions, this abnormality reaches a high prevalence and severity degree, with significant effects on the external morphology of the fish. We show that haemal lordosis recovers during the on-growing of Gilthead seabream in sea cages. At the end of the hatchery phase, 1700 seabream juveniles were tagged electronically and examined for the presence of haemal lordosis. Subsequently, their morphology was examined periodically up to the end of the on-growing period. We found that the prevalence of fish with a lordotic external morphology decreased during the studied period by approximately 50%. Interestingly, 27% of the recovered fish presented a completely normal vertebral column. Geometric morphometric analysis showed no significant differences in the body shape between the fish with a recovered normal phenotype and the fish that were normal since the beginning of the on-growing period. Our results provide the first evidence for the recovery of lordosis during the growth of fish. A mechanism with multiple levels of remodeling of abnormal bones is suggested.

Lysozymes are an ancient group of antimicrobial enzymes of the innate immune system. Here we provide a comparative analysis of the evolution and function of lysozymes during early development in fish, the most speciose vertebrate group. In fishes, lineage and species-specific evolution of both C-type (chicken or conventional) and G-type (goose type) genes occurred. Phylogenetic analysis revealed that the teleost lysozyme G-type members group with the tetrapod homologues but the teleost C-type form three different clusters with the tetrapods. Most of the teleost C-type cluster with tetrapod Lyz but there are some that group with the mammalian Lyzl1/2 and LALBA. This suggests that early in gnathostome evolution these genes already existed and that lyzl1/2 and lalba genes are present in fish and tetrapods. Gene synteny analysis to confirm sequence orthologies failed to identify conserved genome regions between teleosts and other vertebrates lysozyme gene regions suggesting that in the ancestral bony fish genome lyz, lyzl1/2, lalba and lyg precursor genes were transposed to different chromosome regions. The homologue of the mammalian lactalbumin (LALBA) gene was identified for the first time in teleosts and was expressed in skin and during egg and larval development. Lysozyme activity was detected in teleost eggs and varied between species and in the gilthead sea bream lyg and lalba transcript abundance differed in eggs and larvae from different brood stock suggesting differences exist in maternal innate immune protection.

Substitution of marine ingredients (FM‐FO) by plant protein and oil sources can modify selenium (Se) levels in feeds. Se plays an important role in the antioxidative defence by forming part of selenoproteins. Se requirements of gilthead sea bream are not accurately determined; therefore, this study was conducted to define Se supplementation levels in low FM‐FO practical diets for sea bream fingerlings. A plant‐based diet containing 0.45 mg Se/kg diet was used as the basal diet. Four other diets were supplemented to contain 0.68, 0.86, 1.00 or 1.70 mg Se/kg diet, supplied as sodium selenite. Sea bream, weighing 12.6 ± 1.4 g, were distributed in triplicate groups per diet and fed for 42 days. Se supplementation up to 1.00 mg Se/kg significantly improved the growth of sea bream, whereas further increase up to 1.70 mg Se/kg diet reduced growth. The results of this study suggest that the optimum dietary levels of sodium selenite in diets with low FM‐FO with basal levels of 0.45 mg Se/kg are around 0.94 mg Se/kg to promote growth of gilthead sea bream juveniles. On the contrary, dietary levels of 1.70 mg Se/kg were found to be excessive and caused growth reduction, increased catalase expression and hydropic degeneration in the liver.

Fish meal is increasingly substituted in diets for gilthead sea bream with ingredients of terrestrial origin which may affect the mineral content and availability. Among these minerals, copper (Cu) is an essential trace element whose excess may have a potential toxic effect. Since ingredients of terrestrial origin have higher Cu levels than marine ones it is important to define the optimal dietary supply of Cu. Therefore, the aim of this study was to evaluate optimal dietary inclusion level of Cu in low FM-FO diets for gilthead sea bream fingerlings. Five practical diets with low FM (10%) and FO (6%) contents were respectively supplemented with 5 levels of CuSO4 to provide 5.5, 7.4, 9.3, 11.0 and 32.0 mg Cu kg⁻¹ diet. Sea bream fingerlings (12.6 ± 1.4 g, mean ± SD) were distributed in 15 tanks with 30 fish per tank in triplicates and randomly assigned one of the dietary treatments. The fish were fed three times a day until apparent visual satiation for 42 days. Growth was recorded at the end of the trial and samples were taken for biochemical, mineral, histology, X-ray and hepatic gene expression analyses. The results obtained suggest that gilthead sea bream fed practical diets based on plant protein sources that provide at least 5.5 mg Cu kg⁻¹ need no additional Cu supplementation, whereas dietary contents of 11–32 mg Cu kg⁻¹ negatively affected gilthead sea bream performance by reducing growth, increasing oxidative risk and inducing hepatic damage and cholestasis. Dietary Cu levels did not affect body weight, SGR, TGC or FCR, denoting that the level in the non-supplemented diet (5.5 mg Cu kg⁻¹) was enough to cover the requirements for growth. However, increasing dietary Cu levels from 5.5 to 9.3 mg/kg⁻¹ up-regulated cat gene expression. On the contrary elevation of dietary Cu levels up to 11.0 and 32.0 mg Cu kg⁻¹ tended to reduce growth and increased liver steatosis, broken cell margin, peripheral nuclei and sinusoid dilatation which are the markers of hepatic damage and cholestasis denoting potential toxic effects of Cu.