Occurrence of skeletal deformities and osteological development in red porgy Pagrus pagrus larvae cultured under different rearing techniques

The present study describes the osteological development and the occurrence of skeletal deformities in red porgy Pagrus pagrus larvae in relation to the intensification of the rearing system. Eggs obtained from natural spawning were cultured under two different rearing systems: intensive (100 eggs l^?1) in 2000 l and semi‐intensive (mesocosm) system (5 eggs l^?1) in 40 000 l conico‐cylindrical tanks. Fish samples were periodically collected along the development from hatching to juveniles at 95 days post hatching (dph). Osteological development, meristic counts and the presence of skeletal deformities were evaluated. Despite the external appearance of the juveniles being similar to wild standards, X‐ray studies revealed a high number of fish (semi‐intensive: 37·8%; intensive: 45·5%) with skeletal deformities. Regardless of the rearing system, no significant interaction was found between the per cent of the most common deformities, axial deviations (lordosis and presence of fused vertebrae). Cranial deformities and kyphosis incidences, however, were significantly higher in intensively cultured P. pagrus. Also, the fused vertebrae in these fish were located mainly in the caudal area instead of pre‐haemal area for semi‐intensively reared P. pagrus. Moreover, a significant interaction was found between the total number of vertebrae and the type of rearing system used; fish from the intensive system showing a higher number of fish with an extra vertebrae (10 abdominal + 15 caudal). Present results suggest a relationship among feeding sequence, osteological development and deformity incidence and location in P. pagrus larvae.     

Senegalese sole bone tissue originated from chondral ossification is more sensitive than dermal bone to high vitamin A content in enriched Artemia

Several studies have evaluated the effects of dietary vitamin A (VA) on the incidence of skeletal deformities during early ontogeny of fish, but little is known about its effects on bones depending on their process of ossification (dermal or chondral). We examined the incidence of skeletal deformities along development (30 and 48 dph) by double staining technique, in dermal (haemal and caudal vertebral bodies) and chondral (neural and haemal spines, epural, parahypural and hypurals) bones in Senegal sole post metamorphosed larvae fed with different dietary VA levels (37 000, 44 666, 82 666 and 203 000 UI total VA kg^?1 DW) during Artemia feeding phase (6–37 dph, at 18°C). Results obtained in this study showed that dietary VA disrupted the skeletogenesis in Senegalese sole post metamorphosed larvae by increasing the incidence of skeletal deformities in the axial skeleton and caudal fin complex, which were dependent on both bone morphogenesis and ossification processes. Fish fed with the highest dietary VA content showed the highest incidence of skeletal deformities and its value increased along ontogeny. However, when we compared the incidence of deformities in skeletal structures considering their ossification process, most skeletal structures derived from chondral ossification showed a significant higher increase in deformity incidences in fish fed an excess of VA (44 666, 82 666 and 203 000 UI kg^?1 DW), however within chondral bones, hypurals deformity incidence only increased in sole larvae fed Artemia highest VA content. In contrast, this dietary dose‐response effect was only noted in dermal bones from fish fed the highest dose of VA (203 000 UI kg^?1 DW). In addition, the incidence of deformities in chondral bones increased even when the dietary imbalance of VA was corrected, whereas dermal bones were not affected at later ages. These results indicated that depending on the ossification process from which different skeletal structures are derived, bones might be differentially affected by high dietary VA content. Those directly originated from the connective tissue with a preliminary cartilage stage were more sensitive to dietary VA excess than those formed by intramembranous ossification.     

Use of meristic counts and skeletal anomalies to assess developmental plasticity of farmed rainbow trout (Oncorhynchus mykiss,Walbaum 1792): a preliminary study

Rainbow trout is the longest‐standing intensively‐reared species in Western countries, where it has been subjected by farmers to selection for productive traits for more than a century. One interesting aspect in this context is to try and understand if prolonged artificial selection has in some way altered the phenotypic plasticity of this species. In this preliminary study, we characterized meristic counts and skeletal abnormalities in two different (Italian and French) rainbow trout strains, reared during on‐growing following different approaches (intensive and semi‐intensive), in order to analyze whether there are any differences in the skeletal elements and if so, what. Despite the different genetic origin and rearing methodologies to which the lots analyzed were subjected, the occurrences of malformed and seriously malformed individuals were not significantly different, nor were the mean number of anomalies per specimen. The body region most affected by deformities was the caudal vertebral column in both lots, although the French lot was also characterized by an high occurrence of spinal anomalies in the haemal region. Among the meristic counts, only the number of anal and dorsal rays showed statistically different median values between the two lots.     

Effect of rearing techniques on skeletal deformities and osteological development in red porgy Pagrus pagrus (Linnaeus, 1758) larvae

Red porgy is a candidate species for marine aquaculture diversification. The objective of the present study was to describe the osteological development in this species and the occurrence of skeletal deformities in relation to the intensification of the rearing system. Fish samples were periodically collected along the development from hatching to juveniles (95 days after hatching). Osteological development and the presence of skeleton abnormalities were evaluated. Larvae reared under S‐IS showed a better growth in terms of total length in comparison with IS reared ones. Regarding to osteological development for red porgy, this was similar between fish from both culture systems, but differing in timing of apparition and ossification of skeletal elements. X‐ray studies revealed a high number of fish with skeletal deformities (Semi‐intensive: 38.8%; Intensive: 46.5%), but no significant effect of the rearing technique on the incidence of deformities such as lordosis or fused vertebrae was found. However, cranial abnormalities and kyphosis incidences were significantly higher in intensive system cultured red porgy. These results, suggest a relationship among rearing technique, osteological development and the apparition of certain deformities.     

Environmental Conditioning of Skeletal Anomalies Typology and Frequency in Gilthead Seabream (Sparus aurata L., 1758) Juveniles

In this paper, 981 reared juveniles of gilthead seabream (Sparus aurata) were analysed, 721 of which were from a commercial hatchery located in Northern Italy (Venice, Italy) and 260 from the Hellenic Center for Marine Research (Crete, Greece). These individuals were from 4 different egg batches, for a total of 10 different lots. Each egg batch was split into two lots after hatching, and reared with two different methodologies: intensive and semi-intensive. All fish were subjected to processing for skeletal anomaly and meristic count analysis. The aims involved: (1) quantitatively and qualitatively analyzing whether differences in skeletal elements arise between siblings and, if so, what they are; (2) investigating if any skeletal bone tissue/ossification is specifically affected by changing environmental rearing conditions; and (3) contributing to the identification of the best practices for gilthead seabream larval rearing in order to lower the deformity rates, without selections. The results obtained in this study highlighted that: i) in all the semi-intensive lots, the bones having intramembranous ossification showed a consistently lower incidence of anomalies; ii) the same clear pattern was not observed in the skeletal elements whose ossification process requires a cartilaginous precursor. It is thus possible to ameliorate the morphological quality (by reducing the incidence of severe skeletal anomalies and the variability in meristic counts of dermal bones) of reared seabream juveniles by lowering the stocking densities (maximum 16 larvae/L) and increasing the volume of the hatchery rearing tanks (minimum 40 m³). Feeding larvae with a wide variety of live (wild) preys seems further to improve juvenile skeletal quality. Additionally, analysis of the morphological quality of juveniles reared under two different semi-intensive conditions, Mesocosm and Large Volumes, highlighted a somewhat greater capacity of Large Volumes to significantly augment the gap with siblings reared in intensive (conventional) modality.     

Functional differentiation of bmp2a and bmp2b genes in zebrafish

Bone morphogenetic protein 2 plays an important role in the regulation of osteoblast proliferation and differentiation. Phylogenetic analysis showed that the bmp2 ortholog evolved from the same ancestral gene family in vertebrates and was duplicated in teleost, which were named bmp2a and bmp2b. The results of whole-mount in situ hybridization showed that the expression locations of bmp2a and bmp2b in zebrafish were different in different periods (24 hpf, 48 hpf, 72 hpf), which revealed potential functional differentiation between bmp2a and bmp2b. Phenotypic analysis showed that bmp2a mutations caused partial rib and vertebral deformities in zebrafish, while bmp2b^−/− embryos died massively after 12 hpf due to abnormal somite formation. We further explored the expression pattern changes of genes (bmp2a, bmp2b, smad1, fgf4, runx2b, alp) related to skeletal development at different developmental stages (20 dpf, 60 dpf, 90 dpf) in wild-type and bmp2a^−/− zebrafish. The results showed that the expression of runx2b in bmp2a^−/− was significantly downregulated at three stages and the expression of other genes were significantly downregulated at 90 dpf compared with wild-type zebrafish. The study revealed functional differentiation of bmp2a and bmp2b in zebrafish embryonic and skeletal development.     

Effects of phosphorus and vitamin C deficiency,vitamin A toxicity,and lipid peroxidation on skeletal abnormalities in Atlantic halibut (Hippoglossus hippoglossus)

Dietary nutrients play an important role in skeletal tissue metabolism of fish. Deficiency and toxicity of certain nutrients have been linked to bone deformities in larval and juvenile fish. The pathogenesis of skeletal disorders in larval and juvenile fish from the same genetic stock, cultured under similar environment conditions is often difficult to distinguish when marginal deficiencies of multiple nutrients are involved. A study was conducted to characterize the skeletal deformities linked to the deficiency of phosphorus and ascorbic acid, vitamin A toxicity and lipid peroxidation in juvenile halibut. Five experimental diets containing a low level of phosphorus (0.5% dry matter basis), no vitamin C supplement, high level of vitamin A (80 000 IU kg^?1) and oxidized marine fish oil (peroxide value, 7.53 meq kg^?1) and a control diet based on cod fillet and vitamin free casein were fed to juvenile Atlantic halibut for 14 weeks in an attempt to characterize the skeletal deformities. Phosphorus, ascorbic acid, retinol, and α‐tocopherol concentrations of liver and kidney were measured at 0 and 14 weeks. Reduced vertebral ash and phosphorus content were observed in fish fed the low phosphorus diet. Skeletal abnormalities included abnormal hemal and neural spines in the hemal region and scoliosis in the cephalic and hemal regions of the vertebral column. Hepatic and kidney ascorbic acid concentrations were significantly lower in the group fed no ascorbic acid supplement. Skeletal abnormalities were scoliosis and lordosis primarily in the hemal region of the vertebral column. High levels of vitamin A in the diet caused increased hepatic retinol content and scoliosis spanning the cephalic/prehemal and anterior hemal regions of the vertebral column. Fish fed the oxidized oil diet showed increased thiobarbituric acid (TBA) value in the liver and muscle tissue with no significant decrease in hepatic vitamin E concentration. The most frequent skeletal deformity observed was scoliosis, spanning the cephalic/prehemal regions as well as the anterior hemal region of the vertebral column. The pattern and type of abnormalities observed in fish fed these experimental diets were similar to those observed in a commercial halibut hatchery.     

Progress in modeling quality in aquaculture: an application of the Self‐Organizing Map to the study of skeletal anomalies and meristic counts in gilthead seabream (Sparus aurata,L. 1758)

One of the most common drawbacks of artificial life conditions imposed by aquaculture is the quite high presence of skeletal anomalies (SAs) in reared fish, which reduce both functional performances and marketing image/commercial value of the reared lots. Thus, skeletal malformations and their incidence are one of the most important factors affecting fish farmer’s production costs, and several efforts have been due to develop appropriate tools in detecting patterns of co‐variation among rearing parameters and fish quality. In this paper we explore the advantages of using Self‐Organized Maps (SOMs) when dealing with the analysis of correlations between the pattern of SA presence and rearing parameters in gilthead seabream (Sparus aurata L.), that is a largely reared fish of high commercial value. SOM, which is one of the best known neural networks with unsupervised learning rules, were applied to develop a model of the occurrence of SAs, both in terms of type and quantity, in seabream lots from different rearing approaches (extensive, semi‐intensive and intensive). The trained SOMs classified lots according to the variation observed in the different weights of SAs, but also allows the detection of a series of correspondence, namely between: (i) the patter of SAs occurrence and the different rearing approach currently used in seabream aquaculture; and (ii) the total SAs incidence and the variability of meristic counts, represent a completely independent dataset. Mesocosms resulted the best rearing approach to produce wild‐like fish, whereas intensive rearing is characterized by the large presence of SA. Globally, results suggested that this approach is reliable to be used for estimate the distance between aquaculture products and the wild‐like phenotype used as quality reference.     

Skeletal characterization of wild and reared zebrafish: anomalies and meristic characters

Among two groups of wild and reared zebrafishes (zf) Danio rerio, all meristic characters considered were variable except the numbers of rays and pterygophores of the dorsal fin and the principal caudal fin rays, which tended to be canalized. Wild and reared individuals differed in the number of intervertebrae and anal pterygophores, and the dorsal and anal fin insertion. There were some skeletal anomalies of vertebrae and fins, particularly the caudal fin. Cephalic and Weber-apparatus anomalies were rare. Types and frequencies of anomalies were quite similar in the two zf groups, but differences emerged for several less frequent anomalies. Such differences and the phenotypic variability of D. rerio make this species a perfect teleost model for investigating the influence of experimental or unfavourable environmental conditions on skeletal development of both domesticated and wild fish.     

Novel model of restricted mobility induced osteopenia in zebrafish

Immobilization, such as prolonged bed rest, is a risk factor for bone loss in humans. Motivated by the emerging utility of zebrafish (Danio rerio) as an animal of choice for the study of musculoskeletal disease, here we report a model of restricted mobility induced osteopenia in adult zebrafish. Aquatic tanks with small cubical compartments to restrict the movement and locomotion of single fish were designed and fabricated for this study. Adult zebrafish were divided into two groups: a normal control (CONT) and a restricted mobility group (RMG) (18 fish/group). Six fish from each group were euthanized on days 14, 21 and 35 of the movement restriction. By using microcomputed tomography (micro-CT), we assessed bone volume/tissue volume (BV/TV) and bone density in the whole skeleton of the fish. Furthermore, we assessed skeletal shape in the vertebrae (radius, length, volume, neural and haemal arch aperture areas, neural and haemal arch angle, and thickness of the intervertebral space), single vertebra bone volume and bone density. Movement restriction significantly decreased vertebral skeletal parameters such as radius, length, volume, arch aperture areas and angles as well as the thickness of the intervertebral space in RMG. Furthermore, restricted mobility significantly (P < 0.001) decreased BV/TV and bone density as compared to the CONT group, starting as early as 14 days. By analysing zebrafish from CONT and RMG, we show that micro-CT imaging is a sensitive method to quantify distinct skeletal properties in zebrafish. We further defined the micro-CT parameters which can be used to examine the effects of restricted mobility on the skeleton of the fish. Our findings propose a rapid and effective osteopenia “stabulation” model, which could be used widely for osteoporosis drug screening.     

Effect of saddleback syndrome and vertebral deformity on the body shape and size in hatchery-reared juvenile red spotted grouper, Epinephelus akaara (Perciformes: Serranidae): a geometric morphometric approach

This study examined how saddleback syndrome (SBS) and vertebral deformity affect the body shape and size of juvenile stage red spotted grouper, Epinephelus akaara, using the landmark‐based geometric morphometrics method. According to the criterion of skeletal conditions, three groups, i.e. vertebral deformity, SBS, and normal groups, were identified. The results revealed significant differences in body shape among the three groups, in which the vertebral‐deformed group had the deepest mid‐body, the broadest anterior part, and a shortened caudal peduncle, while the SBS group showed the shallowest mid‐body and the narrowest anterior part. The normal group had a body shape intermediate between the vertebral and SBS groups. A comparison of body size among the three groups revealed significant differences in centroid size, with the vertebral‐deformed and SBS groups showing smallest and largest centroid size, respectively. This study illuminates that not all skeletal deformities lead to smaller body size. We suggest that rearing conditions might have caused the deformities reported herein.     

肌间刺缺失对斑马鱼骨骼发育的影响

利用斑马鱼(Danio rerio)野生型与肌间刺完全缺失突变型个体, 从骨骼染色和骨骼发育相关基因表达两方面, 初步评价了肌间刺缺失对斑马鱼骨骼发育的影响。通过骨骼染色对比观察了两种肌间刺表型个体受精后8dpf(days post fertilization, dpf)到56dpf的骨骼发育情况, 结果显示, 两种肌间刺表型除肌间刺外, 其他骨骼发育基本同步。此外, 通过qRT-PCR实验检测分析了6个骨骼发育相关基因(bmp2a、bmp4、smad1、smad4a、runx2a和sp7)在不同肌间刺表型5个胚胎发育时期(3hpf囊胚期、6hpf原肠胚期、12hpf体节期、24hpf咽囊期和72hpf孵化期)和5个胚后生长阶段(15、30、45、60和75dpf)的表达情况。结果显示:在胚胎发育时期, 野生型和突变型个体中bmp2a、bmp4、smad1、smad4a基因和突变型个体中sp7基因的表达均呈现先升后降的变化趋势, 且在体节期达到最高表达水平;野生型和突变型个体中runx2a基因和野生型个体中sp7基因则表现为逐渐上升的趋势。6个基因在囊胚期和原肠胚期表达量无显著差异, bmp2a的表达水平在体节期、咽囊期和孵化期无显著差异, 野生型个体bmp4、smad1、smad4a、runx2a基因在体节期、咽囊期和孵化期的表达水平明显高于突变型, 而sp7基因则表现为突变型明显高于野生型。胚后发育阶段 6个基因在5个生长阶段均呈现逐渐下降的趋势, 且在两种肌间刺表型间其表达仅在个别时期差异显著。综上所述, 肌间刺的缺失对斑马鱼骨骼发育表现型无显著影响, 只在胚胎发育时期影响骨骼相关基因表达水平的变化;结合骨骼染色结果, 推测肌间刺缺失对斑马鱼骨骼发育无显著影响。     

A possible relation between growth and number of deformed vertebrae in Atlantic salmon (Salmo salar L.)

The aim of the present study was to elucidate whether vertebral deformities influence on the growth performance of salmon, and if so, at what level of severity the growth performance/welfare is affected. To do this, Atlantic salmon postsmolts were individually tagged and reared in a common seacage from January 2005 until January 2006. At the end of the experiment, dissected vertebral columns were radiographed, evaluated for vertebral deformities, and the location and type of deformity was recorded. For statistical analysis the fish were grouped according to the number of deformed (d) vertebrae (v); 0 dv (n = 173), 1–5 dv (n = 43), 6–10 dv (n = 11), 11–20 dv (n = 18) and 21–44 dv (n = 31). In fish with less than six dv, the deformities were found within the tail fin region (v 50‐58). Fish with 11–20 dv also had a high occurrence of dv within the tail region (V31‐49), and fish with more than 20 dv also had a high occurrence of dv within the caudal trunk region (V9‐30). Growth was significantly influenced by the number of dv. At the end of the experiment, fish with more than 10 dv were shorter and had a higher condition factor than normal fish, and fish with more than 20 dv were shorter, had lower weight and a higher condition factor than normal fish. In the first period in seawater (January–June) there was no detectable differences in growth (length or weight) between the groups, but the condition factor of the individuals with a high number of dv increased. In the second period (June–January), fish with more than 10 dv, had a significantly lower growth rate. This study indicate that a low occurrence of vertebral deformities have little effect on the growth performance/welfare of salmon.     

Normal axial skeleton structure in common roach Rutilus rutilus (Actinopterygii: Cyprinidae) and malformations due to radiation contamination in the area of the Mayak (Chelyabinsk Province, Russia) nuclear plant

This study was designed to describe normal axial skeletal structure in common roach Rutilus rutilus from putative unaffected environmental conditions, and the occurrence of skeletal malformations in the fish from an area under radiation contamination. Specimens were collected from water bodies of the Techa Cascade Reservoirs located near the Mayak atomic industry plant in the River Ob' drainage, Chelyabinsk Province, Russia. One sample was collected from Lake Irtyash, a reservoir of drinkable water, supplying the town of Ozersk, and the other one from a technical reservoir which is a storage of liquid radioactive waste from Mayak and characterized by high radioactive contamination (mostly (90)Sr and (137)Cs). A comparison was made with historical material collected from the River Ob' before the middle of the 20th century, i.e. before the environment became affected by radioactive contamination. A high number of abnormalities of the axial skeleton were detected in both Mayak samples, in 94 and 97% of examined specimens, in contrast to about 20% in the historical specimens. The abnormalities were in both the unpaired fins and the vertebral column, including the caudal complex and included supernumerary elements, fusions, deformities and displacement of the elements. Most axial skeleton abnormalities, however, were minor, such as splitting, shortening or deformation of spines. Severe defects, such as extensive scolioses, lordoses and kyphoses, were not found. The causes of the abnormalities were not identified in this study, but the high incidence of malformations may be attributed to genetically determined imbalance during development. The almost equal distribution of abnormalities among the fish from non-contaminated and radioactive contaminated reservoirs may be explained by either recent gene flow within the population of R. rutilus in the River Techa system or the effect of unknown unfavourable environmental factors such as chemical pollution.     

Changes in the soluble bone proteome of reared white seabream (Diplodus sargus) with skeletal deformities

One of the main constrains for commercial aquaculture production of white seabream (Diplodus sargus) is the high incidence of skeletal malformations in reared fish. The purpose of this study was to obtain a better understanding of the mechanisms involved in the development of these types of skeletal malformations by comparative proteomic analysis of the vertebral column of normal and deformed fish using 2DE for protein separation and MS for protein identification. We observed a 3.2 and 3.4-fold increase in the expression of two tropomyosin isoforms, one of which (tropomyosin-4) is essential for the motility and polarization cycles of osteoclasts. Furthermore, a 1.6, 1.7 and 1.8-fold increase in three parvalbumin spots was detected, suggesting a cellular response to increased intracellular Ca²⁺ levels. These results can be interpreted as signs of increased cellular activity in the bone of white seabream with skeletal deformities coupled to a higher degree of calcium mobilization, which elicits further studies into the use of these proteins as indicators of skeletal metabolic state.     

Genetic parameters and genotype–environment interactions for skeleton deformities and growth traits at different ages on gilthead seabream (Sparus aurata L.) in four Spanish regions

One of the most important problems of fish aquaculture is the high incidence of fish deformities, which are mainly skeletal. In this study, genetic parameters on gilthead seabream (Sparus aurata L.) for skeleton deformities at different ages (179, 269, 389, 539 and 689 days) and their correlations with growth traits were estimated, as were as their genotype × environment interactions (G × E) at harvesting age. A total of 4093 offspring from the mass spawning of three industrial broodstocks belonging to the PROGENSA^® breeding programme were mixed and on‐grown by different production systems in four Spanish regions: Canary Islands (tanks and cage), Andalusia (estuary), Catalonia (cage) and Murcia (cage). Parental assignment was inferred using the standardized SMsa1 microsatellite multiplex PCR. From three broodstocks, 139 breeders contributed to the spawn and a total of 297 full‐sibling families (52 paternal and 53 maternal half‐sibling families) were represented. Heritabilities at different ages were medium for growth traits (0.16–0.48) and vertebral deformities (0.16–0.41), and low for any type of deformity (0.07–0.26), head deformities (0.00–0.05) and lack of operculum (0.06–0.11). The genetic correlations between growth and deformity traits were medium and positive, suggesting that to avoid increasing deformities they should be taken into account in breeding programmes when growth is selected. The G × E interactions among the different facilities were weak for length and deformity and strong for growth rate during this period. These results highlight the potential for the gilthead seabream industry to reduce the prevalence of deformities by genetic improvement tools.     

Studies on the appearance of skeletal anomalies in red porgy: effect of culture intensiveness,feeding habits and nutritional quality of live preys

Despite the great interest of red porgy as a new species for Mediterranean aquaculture, its commercial production is constrained by the high incidence of skeletal deformities occurring in this species under culture conditions. Several studies have been conducted to better understand the origin of these anomalies in this species, using different system intensiveness, rotifers enrichment products or rotifers docosahexaenoic acid content. The first study showed that culture intensification increased the number of fish with an extra vertebrae, what was probably related to the different nutritional quality of live preys employed in each treatment, since water temperature, salinity and genetic background were identical for the different batches of fish studied. Total incidence of skeletal abnormalities was higher in the intensive system, particularly cranial abnormalities and kyphosis in the cephalic vertebrae. In both rearing systems the most common skeletal anomalies were vertebral column disorders, lordosis and fused vertebrae, their localization along the column being affected by the culture intensiveness. Rotifer enrichment, predominantly its docosahexaenoic acid content significantly affected deformities occurrence. A marked positive effect of rotifer docosahexaenoic acid content was found on larval survival. X‐ray studies denoted elevated levels of bone abnormalities associated, in both trials, to low docosahexaenoic acid content in live preys. Among different anomalies, the presence of fused vertebrae was the most frequent deformity for both rearing trials. A 50% reduction in the number of deformed fish for each type of deformity was obtained when the larvae were fed higher docosahexaenoic acid levels, denoting the important role of this fatty acid in bone development. Further studies are needed to elucidate the importance of essential fatty acids on the development of bone deformities in fish, since the functions of these fatty acids differ among them and can lead to very different effects in fish metabolism, including bone formation.     

Vestiges,rudiments and fusion events: the zebrafish caudal fin endoskeleton in an evo‐devo perspective

The vertebral column results from a controlled segmentation process associated with two main structures, the notochord and the somites. Pathological fusion of vertebral bodies can result from impaired segmentation during embryonic development or occur postnatally. Here, we explore the process of formation and subsequent fusion of the caudalmost vertebral bodies in zebrafish, where fusion is a normal process, mechanically required to support the caudal fin. To reveal whether the product of fusion is on an evolutionary or a developmental scale, we analyze the mode of formation of vertebral bodies, identify transitory rudiments, and characterize vestiges that indicate previous fusion events. Based on a series of closely spaced ontogenetic stages of cleared and stained zebrafish, parasagittal sections, and detection methods for elastin and mineral, we conclude that the formation of the urostyle involves four fusion events. Although fusion of preural 1 (PU1⁺) with ural 1 (U1) and fusion within ural 2 (U2⁺) are no longer traceable during centrum formation (phylogenetic fusion), fusion between the compound centrum [PU1⁺+U1] and U2⁺ (ontogenetic fusion) occurs after individualization of the centra. This slow process is the last fusion and perhaps the latest fusion during the evolution of the zebrafish caudal fin endoskeleton. Newly described characters, such as a mineralized subdivision within U2⁺, together with the reinterpretation of known features in an evolutionary–developmental context, strongly suggest that the zebrafish caudal fin endoskeleton is made from more fused vertebral bodies than previously assumed. In addition, these fusion events occur at different developmental levels depending on their evolutionary status, allowing the dissection of fusion processes that have taken place over different evolutionary times.     

Early development of the postcranial skeleton of the pikeperch Sander lucioperca (Teleostei: Percidae) relating to developmental stages and growth

The early development of the postcranial skeleton (pectoral girdle, pelvic girdle, vertebral column and fins) in pikeperch (Sander lucioperca (L.)) was studied from hatching to days 47 and 43 post fertilization (dpf) at two different rearing temperatures, 15.5 and 18.0°C. Four embryonic and six larval stages were described, ranging from 3.4 ± 0.3 mm to 21.8 ± 2.1 mm in total length. The crucial point in larval development is swimbladder inflation, which enables larvae to swim energy efficiently. Until this time point, only the most essential skeletal elements to enable swimming movements have developed. As the larvae become neutrally buoyant, they grow and differentiate postcranial elements rapidly. Concurrently, swimming performance and foraging success seems to improve. A specific size is correlated with a distinct developmental stage defined by a set of traits that includes the skeletal elements. The developmental sequence of skeletal structures is temperature independent, although growth is slower and the individual developmental stages are reached later at 15.5°C than at 18.0°C. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.