Diving activity of migrating silver eel with and without Anguillicola crassus infection

Infection with the swim bladder nematode Anguillicola crassus has been hypothesised to threaten the spawning migration success of the endangered European eel (Anguilla anguilla). To examine this assumption, we compared the swimming behaviour of one Anguillicola crassus infested eel in the North Sea and three parasite‐free eels in the Baltic using data recovered from data storage tags attached to migrating silver eels. In both areas, eel activity was characterized by frequent diving behaviour throughout the water column during the night, with reduced activity during the day. Despite substantial damage of the swim bladder, the behaviour of the infested eel from the North Sea was within the same range of migrating and diving activity parameters as the three parasite‐free eels from the Baltic Sea. All eels had a similar frequency distribution of descent or ascent speeds and a similar average horizontal migration speed. The diving speeds and dive ranges exclude the possibility that the eels were in continuous hydrostatic equilibrium during their migrations and suggests therefore that the role of the swim bladder in vertical migration is likely to be more complex than currently thought. Our results suggest that eels infested by Anguillicola crassus are capable of diving in a similar manner to uninfested eels during the first stretch of their spawning migration.     

Catalase, glutathione peroxidase, and superoxide dismutase in the rete mirabile and gas gland epithelium of six species of marine fishes

Rete mirabile and gas gland epithelium from the swim bladders of six species of marine fishes were assayed for catalase, glutathione peroxidase, and superoxide dismutase activity. Correlation of the results of these assays with measurements of the concentration of oxygen in the lumen of the normal steady state swim bladders revealed that swim bladders in species containing higher levels of oxygen also exhibited higher levels of superoxide dismutase activity in the rete mirabile/gas gland epithelium region. There appeared to be no correlation between oxygen concentration and the level of catalase or glutathione peroxidase activity. Induction of the inflatory reflex in Opsanus tau by a single deflation of the swim bladder resulted in an increase in the percent of oxygen in the swim bladder lumen 18 to 24 hours later, but this was not accompanied by any significant increases in antioxidant enzyme activity. Swim bladders that were deflated three times at 24-hour intervals showed further increases in oxygen concentration at the end of the 72-hour period but no alteration in superoxide dismutase activity.     

Morphological development of the swim bladder in hatchery-reared striped trumpeter Latris lineata

This study examined swim bladder morphogenesis in three cohorts of striped trumpeter (Latris lineata), a euphysoclist species with physostomous larvae. The swim bladder was first discernible 1–2 days after hatching as an evagination on the dorsal surface of the incipient digestive tract. It comprised a cluster of mesenchymal cells surrounding an inner primordium of epithelial cells. At mouth opening in larvae of 5.3 mm standard length (SL), the swim bladder was noticeably enlarged. Histologically, the swim bladder lumen was dilated and liquid filled. The pneumatic duct was first seen during the dilation stage and the rete mirabile began forming among the connective tissue surrounding the swim bladder. Initial swim bladder inflation occurred on day 11 post‐hatching in Cohort 1, at 14°C, and day 9 post‐hatching, in Cohorts 2 and 3, at 16°C. Histologically, the lumens of inflated swim bladders were ellipsoid and the epithelium was squamous, except for cuboidal gas gland cells at the anterio‐ventral and anterio‐lateral regions of the swim bladder. During the initial inflation interval the pneumatic duct was dilated in larvae both with and without swim bladder inflation. The pneumatic duct began to regress in some larvae over 7.5 mm SL. The swim bladder of striped trumpeter was similar to larvae of other altricial perciform marine fish in respect to organ derivation, tissue differentiation, luminal dilation and initial gaseous inflation. However, variations, particularly the delay in initial swim bladder inflation until after the start of feeding, were observed that could be fundamental to problems encountered during larval rearing.     

Superoxide dismutase,catalase, and glutathione peroxidase in the swim bladder of the physoclistous fish,Opsanus tau L

Summary The antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase were measured in the rete mirabile and gas gland epithelium area of the swim bladder of the toadfish Opsanus tau. When the concentration of enzyme in the swim bladder was compared with the concentration in other organs (kidney, heart, gills) of the same fish, the swim bladder was found to have the highest concentration of superoxide dismutase but relatively low levels of glutathione peroxidase and catalase.Cytochemical assay for the peroxidatic activity of catalase confirmed that virtually no catalase is present in epithelial cells of the gas gland. A similar assay for peroxidase revealed a cyanide-sensitive peroxidase in the multilamellar bodies of these cells. Most of the catalase and peroxidase in the rete mirabile appears to be confined to the granules of neutrophils and the cytoplasm of erythrocytes. Enzyme activity in the neutrophils is not inhibited by 10^-1 M KCN. Cyanide does appear to inhibit the peroxidase activity in erythrocytes but has little effect on catalase in these cells.Supported by grant No. HL23338 from the National Institutes of Health     

Intra‐ and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection

The plainfin midshipman fish, Porichthys notatus , is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra‐ and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro‐computerized tomography revealed that females and type II males have prominent, horn‐like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner‐ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest.     

Dynamics Modeling and Simulation of a Bionic Swim Bladder System in Underwater Robotics

While considering that fish could suspend themselves under water and could enhance their mobility by adjusting its swim bladder, we have carried out research on a bionic swim bladder system in underwater robotics, which could amend the underwater robotics' static balance and controllability conditions even if the depth of water changes. First, this paper introduces the bio-swim bladder's structure and function. Second, it works out the dynamic model of the bionic swim bladder, and then it analyses the dynamic characteristic and effect of the bionic swim bladder system with the software Matlab/simulink. Finally, considering about the nonlinear relationship of the parameters in the model, this paper brings forward a dual-speed control method, which could make the effect of the bionic swim bladder non-coupling. The result of the simulation reveals that the bionic swim bladder could change the buoyancy and centroid distribution of the underwater robotics effectively and independently, bringing it into a balance state, under which the control and maneuverability could be enhanced.     

Swim bladder and posterior lateral line nerve of the nurseryfish, Kurtus gulliveri (Perciformes: Kurtidae)

The morphology of the swim bladder and inner ear of the nurseryfish, Kurtus gulliveri, appear adapted for enhanced pressure wave reception. The saccule is enlarged and surrounded by very thin bone and two large fontanelles that would present reduced resistance to pressure waves. The swim bladder is elaborate, with six dorsolaterally projecting pairs of lobes that are tightly encased in ribs and an additional caudally projecting pair of lobes encased in the first hemal spine. The ribs and musculature surrounding the swim bladder laterally are very thin, so that four or five "rib windows" are readily apparent on back-lit specimens. This swim bladder-rib configuration would also present reduced resistance to pressure waves to enhance function as a peripheral auditory structure. However, high-resolution X-ray computed tomography and dissection reveal no anterior projections of the swim bladder that could serve as a mechanical coupling to the inner ear. The posterior lateral line nerve is well developed and lies directly over the tips of the ribs encasing the swim bladder lobes. This nerve is not, however, associated with a lateral line canal and a lateral line canal is absent on most of the body. We hypothesize that the posterior lateral line nerve transmits mechanosensory information from the swim bladder.     

The buoyancy and orientation of the upside-down catfishes of the genus Synodontis (Pisces: Siluroidei)

The forces involved in the buoyancy of the genus Synodontis are unusually large owing to the well-developed cephalo-nuchal shield possessed by all members of the genus, and the large swim bladder and high levels of body fat needed to counteract this. A new method of determining the quantity of crude lipid in the tissues was developed and tested against a recognized method. Negative correlations were found between the total quantities of fat present and the volumes of the swim bladder for several species. Two species which maintained neutral buoyancy but occupied different ecological niches were found to achieve neutrality by different means, one possessing an abnormally large swim bladder and the other very large quantities of fat. The amount of bone present was found to be considerably greater than in species from other genera.
Several species of this genus regularly invert and swim on their backs. Three of the species known to do this were found amongst the 16 species present in the man-made Lake Kainji on the River Niger in Nigeria. The orientations of many of the species were studied both under natural conditions and in the laboratory. Several possible causes of inversion were investigated, including both physical and behavioural factors. The position of the food source was found to be the most important factor controlling the orientation of the species. By manipulating this it was possible to persuade normally orientating species to invert, and inverting species to return to normal orientation. Three theories to explain the inverting habit are advanced and their merits discussed.     

TGF-β/Smads信号通路介导脯氨酸促进浅色黄姑鱼鱼鳔胶原蛋白沉积

为了进一步验证转化生长因子(TGF-β) /Smads信号通路在脯氨酸(Pro)促进鱼鳔胶原蛋白沉积中的作用, 研究利用TGF-β/Smads通路抑制剂干扰, 分析干扰前后鱼鳔中胶原蛋白含量及相关基因转录水平的变化。根据前期实验获得的Pro最佳添加量, 制定饲料配方, 饲喂浅色黄姑鱼1月后, 通过腹腔注射氧化苦参碱(Oxymatrine)为期1个月。在实验结束后, 测量各项指标, 评估干扰前后, Pro促进鱼鳔胶原蛋白沉积的效果及变化。实验结果表明: Pro能显著上调TGF-β/Smads通路中相关基因的表达, 并促进鱼鳔胶原蛋白沉积, Oxymatrine干扰显著下调了TGF-β/Smads通路中相关基因(Col1α1、Col1α2、TGF-β和Smad2)表达, 同时导致鱼鳔中胶原蛋白沉积下降。由此推断Pro通过激活TGF-β/Smads通路促进鱼鳔中胶原蛋白沉积, 而Oxymatrine干扰抑制了TGF-β/Smads通路, 导致Smad2与Col1α2启动子结合受阻, 进而下调了Col1α2基因的转录, 从而降低鱼鳔中胶原蛋白的沉积。综上表明, TGF-β/Smads信号通路在Pro促进浅色黄姑鱼鱼鳔胶原蛋白沉积过程中起着重要调控作用, 其中Col1α1、Col1α2、TGF-β和Smad2扮演着重要角色, 研究结果可为鱼类胶原蛋白代谢的营养调控提供新思路和新方法。     

Effects of exposure to pile-driving sounds on the lake sturgeon,Nile tilapia and hogchoker

Pile-driving and other impulsive sound sources have the potential to injure or kill fishes. One mechanism that produces injuries is the rapid motion of the walls of the swim bladder as it repeatedly contacts nearby tissues. To further understand the involvement of the swim bladder in tissue damage, a specially designed wave tube was used to expose three species to pile-driving sounds. Species included lake sturgeon (Acipenser fulvescens)—with an open (physostomous) swim bladder, Nile tilapia (Oreochromis niloticus)—with a closed (physoclistous) swim bladder and the hogchoker (Trinectes maculatus)—a flatfish without a swim bladder. There were no visible injuries in any of the exposed hogchokers, whereas a variety of injuries were observed in the lake sturgeon and Nile tilapia. At the loudest cumulative and single-strike sound exposure levels (SEL_cum and SEL_ss respectively), the Nile tilapia had the highest total injuries and the most severe injuries per fish. As exposure levels decreased, the number and severity of injuries were more similar between the two species. These results suggest that the presence and type of swim bladder correlated with injury at higher sound levels, while the extent of injury at lower sound levels was similar for both kinds of swim bladders.     

Monthly changes in the swim bladder morphology of the female Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> in the coastal waters of Mikawa Bay,Japan

In the coastal area of Mikawa Bay, central Japan, specimens of the female Japanese eel Anguilla japonica could be divided into two groups according to the degree of swim bladder development. In one case, they were undeveloped, and in the other, they were highly developed with large rete mirabile, thick submucosa, and a well-developed gas gland. The morphology of the swim bladder in the latter group was comparable with that in the artificially fully maturated eel. The specimens with an undeveloped swim bladder were caught during all months, although their number was small. The specimens with a highly developed swim bladder were most abundant in November and December. During these months, catch of the specimens also increased sharply, by more than 10 fold compared to that in other months. These observations indicate that most of the eel appearing in coastal Mikawa Bay from October to January have a highly developed swim bladder adapted for a deep-sea environment. It was also conjectured that these specimens most likely migrated from rivers feeding into Mikawa Bay, toward spawning grounds in the open sea, and that this occurred after development of their swim bladders was completed. Actually, the specimens caught in the upstream of the Toyo River feeding into Mikawa Bay from late August to early October already had highly developed swim bladders.     

A novel in-vitro system for the simultaneous exposure of bladder smooth muscle cells to mechanical strain and sustained hydrostatic pressure

The novel hydrostrain system was designed in an effort to establish and maintain conditions that simulate the in-vivo mechanical environment of the bladder. In this laboratory system, ovine bladder smooth muscle cells on flexible, 10-cm-dia silastic membranes were exposed simultaneously to hydrostatic pressure (40 cm H2O, a pressure level currently associated with bladder pathologies) and mechanical strains (up to 25 percent) under standard cell culture conditions for 7 h. Under these conditions, Heparin Binding-Epidermal Growth Factor and Collagen Type III mRNA expression were significantly increased (p<0.01 and 0.1, respectively); however, no changes were observed in Collagen Type I mRNA expression. Decreases in the Collagen Type I:Type III ratio following simultaneous exposure of bladder smooth muscle cells to pathological levels of hydrostatic pressure and mechanical strain in vitro are in agreement with clinically observed increases in Collagen Type III with concomitant decreased human bladder compliance. The results of the present study, therefore, provide cellular/molecular level information relevant to bladder pathology that could have significant implications in the field of clinical urology.     

Relationship between Swim Bladder Morphology and Hearing Abilities-A Case Study on Asian and African Cichlids

Background

Several teleost species have evolved anterior extensions of the swim bladder which come close to or directly contact the inner ears. A few comparative studies have shown that these morphological specializations may enhance hearing abilities. This study investigates the diversity of swim bladder morphology in four Asian and African cichlid species and analyzes how this diversity affects their hearing sensitivity.

Methodology/Principal Findings

We studied swim bladder morphology by dissections and by making 3D reconstructions from high-resolution microCT scans. The auditory sensitivity was determined in terms of sound pressure levels (SPL) and particle acceleration levels (PAL) using the auditory evoked potential (AEP) recording technique. The swim bladders in Hemichromis guttatus and Steatocranus tinanti lacked anterior extensions and the swim bladder was considerably small in the latter species. In contrast, Paratilapia polleni and especially Etroplus maculatus possessed anterior extensions bringing the swim bladder close to the inner ears. All species were able to detect frequencies up to 3 kHz (SPL) except S. tinanti which only responded to frequencies up to 0.7 kHz. P. polleni and E. maculatus showed significantly higher auditory sensitivities at 0.5 and 1 kHz than the two species lacking anterior swim bladder extensions. The highest auditory sensitivities were found in E. maculatus, which possessed the most intimate swim bladder-inner ear relationship (maximum sensitivity 66 dB re 1 µPa at 0.5 kHz).

Conclusions

Our results indicate that anterior swim bladder extensions seem to improve mean absolute auditory sensitivities by 21–42 dB (SPLs) and 21–36 dB (PALs) between 0.5 and 1 kHz. Besides anterior extensions, the size of the swim bladder appears to be an important factor for extending the detectable frequency range (up to 3 kHz).     

The laterophysic connection and swim bladder of butterflyfishes in the genus Chaetodon (Perciformes: Chaetodontidae)

The laterophysic connection (LC) is an association between bilaterally paired, anterior swim bladder extensions (horns) and medial openings in the supracleithral lateral line canals that diagnoses butterflyfishes in the genus Chaetodon. It has been hypothesized that the LC makes the lateral line system sensitive to sound pressure stimuli that are transmitted by the swim bladder horns and converted to fluid flow into the lateral line system via a laterophysic tympanum. The purpose of this study was to define variation in the morphology of the LC, swim bladder and swim bladder horns among 41 Chaetodon species from all 11 Chaetodon subgenera and a species from each of four non-Chaetodon genera using gross dissection, histological analysis as well as 2D or 3D CT (computed tomographic) imaging of live, anesthetized fishes. Our results demonstrate that the lateral line system appears rather unspecialized with well-ossified narrow canals in all species examined. Two LC types (direct and indirect), defined by whether or not the paired anterior swim bladder horns are in direct contact with a medial opening in the supracleithral lateral line canal, are found among species examined. Two variants on a direct LC and four variants of an indirect LC are defined by combinations of soft tissue anatomy (horn length [long/short] and width [wide/narrow], number of swim bladder chambers [one/two], and presence/absence of mucoid connective tissue in the medial opening in the supracleithrum). The combination of features defining each LC variant is predicted to have functional consequences for the bioacoustics of the system. These findings are consistent with the recent discovery that Chaetodon produce sounds during social interactions. The data presented here provide the comparative morphological context for the functional analysis of this novel swim bladder-lateral line connection.     

Development of the ear, hearing capabilities and laterophysic connection in the spotfin butterflyfish (Chaetodon ocellatus)

The ontogeny of the ear, swim bladder and laterophysic connection was investigated in the spotfin butterflyfish, Chaetodon ocellatus in order to determine how the development of the laterophysic connection (a Chaetodon synapomorphy) is correlated with ontogenetic changes in the hearing capabilities in these abundant and ecologically important coral reef fishes. Histological and cleared and stained material revealed that the medial opening in the lateral line canal in the supracleithrum (which defines the laterophysic connection), an inflated physoclistous swim bladder, and the three otolithic organs are already present in the smallest individuals examined (7?C15?mm SL). The medial opening in the supracleithrum increases in size and the cylindrical swim bladder horns form after the loss of the head plates characteristic of the tholichthys stage, in individuals ??29?mm SL. The three sensory maculae of the ear increase in size, and the shape of the sacculus changes most dramatically with fish growth; hair cell density is highest in the utriculus. Physiological analysis of the reponse to sound pressure showed that larval and juvenile C. ocellatus had a hearing sensitivity peak at 100?C200?Hz, which was ~30?C40?dB more sensitive than that measured in larval coral reef fishes (e.g., damselfishes) that lack swim bladder horns. C. ocellatus did not show any ontogenetic changes in sensitivity to sound pressure, which may be explained by the fact that the growth of the swim bladder horns maintains the small distance between the swim bladder and ear that was established earlier during the larval stage. The timing of the development of the swim bladder horns suggests that if the laterophysic connection has a sensory acoustic function, its presence in individuals >29?mm SL suggests that its role is limited to post-settlement, reef-based behaviors.     

Morphological and histological changes in the swim bladder during maturation of the Japanese eel

Silver eels Anguilla japonica ( I _G 1·5–3·5) had more developed rete mirabile, gas gland and submucosa than yellow eels ( I _G 0·4–1·5) and the development of swim bladder components increased with sexual maturity only in the early maturation process ( I _G 3·5). These observations indicate that the Japanese eel develops its swim bladder in either the river or shallow sea water and leaves for the open sea after the swim bladder has become adapted to a deeper-sea environment.     

Distribution and Relative Size of the Swim Bladder in Percina, With Comparisons to Etheostoma, Crystallaria, and Ammocrypta (Teleostei: Percidae)

The distribution of the swim bladder was examined in 20 species representing all four genera (Percina, Etheostoma, Crystallaria, and Ammocrypta) of darters (Etheostomatini). Including data on species examined in other studies, swim bladders have been found in 15 of 17 species of Percina, but were absent in Crystallaria asprella, Ammocrypta pellucida, and the 18 species of Etheostoma examined. Relative swim bladder length in Percina was shown to be positively correlated with body size. Although not statistically significant, swim bladder size also correlates with habitat (riffle, run, or pool) and swimming behavior (midwater or benthic).     

The fatty acid chain elongase,Elovl1, is required for kidney and swim bladder development during zebrafish embryogenesis

Very long chain fatty acids are required for sphingolipid synthesis, lipid homeostasis, myelin formation, epidermal permeability, and retinal function. Seven different enzymes are known to be involved in the elongation cycle of fatty acids, with different chain-length specificities. Elovl1 is one of those enzymes whose function has been linked mainly to the synthesis of sphingolipids and the epidermal barrier. However, the role of Elovl1 in organogenesis is not clear. In zebrafish, 2 Elovl1 genes, elovl1a and elovl1b, are highly expressed in the swim bladder, and elovl1b is also expressed in the kidney. We found that both elovl1 knockdown embryos contain increased levels of long chain fatty acids from carbon number 14 to 20 as compared to control embryos. Oil-Red-O staining shows that yolk lipid consumption is greatly reduced, whereas lipid droplets accumulate within the swim bladder. Notably, knockdown of either elovl1a or elovl1b affects the expression of genes involved in swim bladder development and impairs inflation of the swim bladder. Consistent with its expression in the pronephros, knockdown of elovl1b alone affects the expression of genes required for kidney development and reduces renal clearance. Our findings strongly suggest that both elovl1 genes are a key determinant of swim bladder and kidney development in zebrafish, which may be comparatively applicable to lung and kidney development in humans.     

Does the Hearing Sensitivity in Thorny Catfishes Depend on Swim Bladder Morphology?

Background

Thorny catfishes exhibit large variations in swim bladder morphology. These organs are of different sizes, forms and may have simple or branched diverticula. The swim bladder plays an important role in otophysans because it enhances their hearing sensitivity by transmitting sound pressure fluctuations via ossicles to the inner ear.

Methodology/Principal Findings

To investigate if a form-function relationship exists, the swim bladder morphology and hearing ability were analyzed in six species. The morphology was quantified by measuring the length, width and height and calculating a standardized swim bladder length (sSBL), which was then used to calculate the relative swim bladder length (rSBL). Hearing was measured using the auditory evoked potential (AEP) recording technique. Two species had simple apple-shaped and four species heart-shaped (cordiform) bladders. One of the latter species had short unbranched diverticula on the terminal margin, two had a secondary bladder and two had many long, branched diverticula. The rSBL differed significantly between most of the species. All species were able to detect frequencies between 70 Hz and 6 kHz, with lowest thresholds found between 0.5 and 1 kHz (60 dB re 1 µPa). Hearing curves were U-shaped except in Hemidoras morrisi in which it was ramp-like. Mean hearing thresholds of species possessing smaller rSBLs were slightly lower (maximum 8.5 dB) than those of species having larger rSBLs.

Conclusions/Significance

The current findings reveal a relationship between swim bladder form and its function among thorny catfishes. Relatively smaller swim bladders resulted in relatively better hearing. This is in contrast to a prior inter-familial study on catfishes in which species with large unpaired bladders possessed higher sensitivity at higher frequencies than species having tiny paired and encapsulated bladders.