The role of starter diets in the development of skeletal abnormalities in zebrafish Danio rerio (Hamilton, 1822).

Fish skeletal development has long been correlated with nutritional factors. Lack of zebrafish nutritional standardization, especially during the early stages, decreases the reproducibility of the conducted research. The present study represents an evaluation of four commercial (A, D, zebrafish specific; B, generic for freshwater larvae; C, specific for marine fish larvae) and one experimental (Ctrl) early diets on zebrafish skeletal development. Skeletal abnormalities rates in the different experimental groups were assessed at the end of the larval period (20 days post-fertilization, dpf) and after a swimming challenge test (SCT, 20-24 dpf). At 20 dpf, results revealed a significant effect of diet on the rate of caudal-peduncle scoliosis and gill-cover abnormalities, which were relatively elevated in B and C groups. SCT results focused on swimming-induced lordosis, which was comparatively elevated in diets C and D (83% ± 7% and 75% ± 10%, respectively, vs. 52% ± 18% in diet A). No significant effects of dry diets were observed on the survival and growth rate of zebrafish. Results are discussed with respect to the deferential diet composition between the groups and the species requirements. A potential nutritional control of haemal lordosis in finfish aquaculture is suggested.

Body-shape trajectories and their genetic variance component in Gilthead seabream (Sparus aurata L.).

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 (h2) of the final phenotype ranged from 0.370 ± 0.077 to 0.511 ± 0.089, whereas h2 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.

Balancing between Artemia and microdiet usage for normal skeletal development in zebrafish (Danio rerio).

Targeting in zebrafish fast growth, high survival rates and improved reproductive performance has led over the last years in variable feeding regimes between different facilities. Despite its significance on fish function and welfare, normal skeletal development has rarely been evaluated in establishing the best feeding practices for zebrafish. The aim of this study was to establish a protocol for normal skeletal development, growth and survival of zebrafish larvae through live feed-to-microdiet transition at an appropriate rate. Four feeding regimes including feeding exclusively on Artemia nauplii (A) or dry microdiet (D), and feeding on both Artemia and microdiet at two different transition rates (slow (B) or fast (C)) were applied from 5 to 24 dpf (days post-fertilization). Results demonstrated a significant effect of feeding regimes on the incidence of skeletal abnormalities (gill cover, fins and vertebral column, p < .05) in zebrafish larvae. The A and B experimental groups presented the highest (88 ± 3 and 84 ± 17%, respectively), but the C and D the lowest (18 ± 14 and 11 ± 2%, respectively), rates of normal fish (fish without any abnormality). Similarly, growth rate was comparatively elevated in A and B groups. No significant differences were observed in fish survival between A, B and C groups. However, D group presented a significantly lower survival rate. To our knowledge, this is the first study to show that the live feed-to-microdiet transition rate influences larval growth, survival and abnormality rates in a non-homogenous pattern.

Exercise-induced lordosis in zebrafish Danio rerio (Hamilton, 1822).

The anabolic effect of exercise on muscles and bones is well documented. In teleost fish, exercise has been shown to accelerate skeletogenesis, to increase bone volume, and to change the shape of vertebral bodies. Still, increased swimming has also been reported to induce malformations of the teleost vertebral column, particularly lordosis. This study examines whether zebrafish (Danio rerio) develops lordosis as a result of continuous physical exercise. Zebrafish were subjected, for 1 week, to an increased swimming exercise of 5.0, 6.5 or 8.0 total body lengths (TL) per second. Control and exercise group zebrafish were examined for the presence of vertebral abnormalities, by in vivo examination, whole mount staining for bone and cartilage and histology and micro-computed tomography (CT) scanning. Exercise zebrafish developed a significantly higher rate of lordosis in the haemal part of the vertebral column. At the end of the experiment, the frequency of lordosis in the control groups was 0.5 ± 1.3% and that in the exercise groups was 7.5 ± 10.6%, 47.5 ± 10.6% and 92.5 ± 6.0% of 5.0, 6.5 and 8.0 TL∙s-1 , respectively. Histological analysis and CT scanning revealed abnormal vertebrae with dorsal folding of the vertebral body end plates. Possible mechanisms that trigger lordotic spine malformations are discussed. This is the first study to report a quick, reliable and welfare-compatible method of inducing skeletal abnormalities in a vertebrate model during the post-embryonic period.

Recovery of haemal lordosis in Gilthead seabream (Sparus aurata L.).

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.

The development of contemporary European sea bass larvae (Dicentrarchus labrax) is not affected by projected ocean acidification scenarios.

Ocean acidification is a recognized consequence of anthropogenic carbon dioxide (CO2) emission in the atmosphere. Despite its threat to marine ecosystems, little is presently known about the capacity for fish to respond efficiently to this acidification. In adult fish, acid-base regulatory capacities are believed to be relatively competent to respond to hypercapnic conditions. However, fish in early life stage could be particularly sensitive to environmental factors as organs and important physiological functions become progressively operational during this period. In this study, the response of European sea bass (Dicentrarchus labrax) larvae reared under three ocean acidification scenarios, i.e., control (present condition, [Formula: see text] = 590 µatm, pH total = 7.9), low acidification (intermediate IPCC scenario, [Formula: see text] = 980 µatm, pH total = 7.7), and high acidification (most severe IPCC scenario, [Formula: see text] = 1520 µatm, pH total = 7.5) were compared across multiple levels of biological organizations. From 2 to 45 days-post-hatching, the chronic exposure to the different scenarios had limited influence on the survival and growth of the larvae (in the low acidification condition only) and had no apparent effect on the digestive developmental processes. The high acidification condition induced both faster mineralization and reduction in skeletal deformities. Global (microarray) and targeted (qPCR) analysis of transcript levels in whole larvae did not reveal any significant changes in gene expression across tested acidification conditions. Overall, this study suggests that contemporary sea bass larvae are already capable of coping with projected acidification conditions without having to mobilize specific defense mechanisms.