Non-inflated Swim Bladder Research Articles

Znf469 Plays a Critical Role in Regulating Synthesis of ECM: A Zebrafish Model of Brittle Cornea Syndrome.

Brittle cornea syndrome (BCS) is a rare autosomal recessive disorder characterized by extreme thinning and fragility of the cornea, and mutations in ZNF469 cause BCS-1. We aimed to establish a znf469 mutant zebrafish line to explore its roles and possible pathogenic mechanism in cornea development and disorder. znf4694del/4del mutant zebrafish was generated using the CRISPR/Cas9 technology. Transmission electron microscopy (TEM) was performed to examine the phenotype of the cornea in different developmental stages. RNA sequencing and quantitative real-time polymerase chain reaction were used to reveal the molecular mechanism. Macroscopically, homozygous znf469 mutant zebrafish larvae exhibited a curved body from 72 hours postfertilization, similar to kyphoscoliosis, and a noninflated swimbladder at 7 days postfertilization (dpf). TEM revealed an extreme reduction of corneal stroma thickness in homozygous znf469 mutant zebrafish in both the central and peripheral cornea from the early development stage. RNA-sequencing analysis demonstrated that the znf469 mutation leads to the decreased synthesis of various extracellular matrix (ECM) components, such as collagens and proteoglycans, but increased synthesis of 26S proteasome family members. The results of our work indicate that znf469 is a critical gene that, as a widely considered transcription factor, may regulate the synthesis and degradation of a large number of ECM components that play an important role in corneal development.

Non-additive mixture effects of benzo[a]pyrene and pesticides in vitro and in vivo: Role of AhR signaling

Polycyclic aromatic hydrocarbons (PAHs) and pesticides are two major groups of environmental contaminants which humans are simultaneously exposed to. However, potential mixture interactions of these groups of chemicals are not well-studied. In this study, the effects of binary mixtures of the PAH benzo[a]pyrene (B[a]P) and the commonly used pesticides chlorpyrifos, paraquat and tebuconazole on human liver HepG2 cells were investigated. The results showed that binary mixtures of B[a]P and paraquat or tebuconazole mainly caused additive effects on cell viability and cytochrome P4501a1 (CYP1A1) expression compared to single compound exposures. In contrast, the binary mixture with chlorpyrifos interacted antagonistically on cell viability and ROS production, whereas synergistic effects were observed for induction of CYP1A1 expression. B[a]P and chlorpyrifos also inhibited the activity of recombinant human CYP1A1 enzyme. To verify the synergistic in vitro results, zebrafish (Danio rerio) embryos were exposed to binary mixtures of B[a]P and chlorpyrifos. The mixtures caused synergistic induction of CYP1A expression, as well as synergistic developmental toxicity on multiple endpoints including non-inflated swim bladder, yolk-sac and pericardial edema, and spinal deformation. The effects were reduced upon morpholino-mediated knockdown of the aryl hydrocarbon receptor (AhR), indicating an AhR-dependence of the synergistic toxicity. Altogether, these data suggest that the combination of AhR activation and CYP1A1 inhibition is responsible for the underlying non-additive interaction between B[a]P and chlorpyrifos in vitro and in vivo.

Loss of sdhb in zebrafish larvae recapitulates human paraganglioma characteristics.

Pheochromocytomas and paragangliomas (PPGLs) caused by mutations in the B-subunit of the succinate dehydrogenase (SDHB) have the highest metastatic rate among PPGLs, and effective systemic therapy is lacking. To unravel underlying pathogenic mechanisms, and to evaluate therapeutic strategies, suitable in vivo models are needed. The available systemic Sdhb knock-out mice cannot model the human PPGL phenotype: heterozygous Sdhb mice lack a disease phenotype, and homozygous Sdhb mice are embryonically lethal. Using CRISPR/cas9 technology, we introduced a protein-truncating germline lesion into the zebrafish sdhb gene. Heterozygous sdhb mutants were viable and displayed no obvious morphological or developmental defects. Homozygous sdhb larvae were viable, but exhibited a decreased lifespan. Morphological analysis revealed incompletely or non-inflated swim bladders in homozygous sdhb mutants at day 6. Although no differences in number and ultrastructure of the mitochondria were observed. Clear defects in energy metabolism and swimming behavior were observed in homozygous sdhb mutant larvae. Functional and metabolomic analyses revealed decreased mitochondrial complex 2 activity and significant succinate accumulation in the homozygous sdhb mutant larvae, mimicking the metabolic effects observed in SDHB-associated PPGLs. This is the first study to present a vertebrate animal model that mimics metabolic effects of SDHB-associated PPGLs. This model will be useful in unraveling pathomechanisms behind SDHB-associated PPGLs. We can now study the metabolic effects of sdhb disruption during different developmental stages and develop screening assays to identify novel therapeutic targets in vivo. Besides oncological syndromes, our model might also be useful for pediatric mitochondrial disease caused by loss of the SDHB gene.

The effect of dissolved carbon dioxide (CO2) on white grouper (Epinephelus aeneus) performance, swimbladder inflation and skeletal deformities

The effect of three seawater CO2 concentrations (0.8±0.18, 5.64±0.64 and 28.58±3mgl−1), was tested on white grouper (Epinephelus aeneus) post-larvae reared at two water temperatures (23 and 27°C) in a 30 aquarium (17l each) experimental system. Forty-five dph fish were stocked per aquarium allowing the testing of the 6 CO2 temperature treatment combinations in replicates of 5aquariatreatment−1 for 60days. The final weight of fish reared under the high CO2 treatment was 25% and 10% (P<0.05) lower than that of fish reared under the control conditions at 23° and 27°C, respectively. A similar pattern in total length (TL) was demonstrated where fish exposed to the high CO2 treatment grew 10 and 7.4% more slowly (P<0.05) than the control at 23° and 27°C, respectively. A large percentage (78.8±6.1%) of fish reared at the control CO2 concentration (0.8±0.18mgl−1) and exposed to 27°C had inflated swimbladders compared to only 17.6±9.2% in fish exposed to the high CO2 concentration (28.58±3mgl−1) at 23°C. Following the 60days of the CO2 and temperature exposure period (45–105dph), 87–100% of the fish from the six treatment combinations, independent of temperature and CO2 exposure history, had inflated swimbladders at 150dph. It was shown that, during the recovery phase (125dph) at 23°C, the ratio between the swimbladder volume and body weight (mm3g−1) in fish exposed to the high CO2 concentration was 4.65±0.79mm3g−1, which was significantly smaller (P<0.05) than 10.12±0.72mm3g−1in the control CO2 treatment. In general, the swimbladder volume was directly correlated with the rearing temperature and was up to 50% larger in fish reared at 27°C compared to those from 23°C independent of CO2 concentration. The relative presence of skeletal deformities in fish with non-inflated swimbladders was 6.49%, which was significantly (P<0.05) higher than the 0.93% in fish with a normally inflated swimbladder. In addition, fish with an uninflated swimbladder demonstrated a significantly (P<0.05) more severe lordosis deformity with a vertebra angle of 47.5±15° compared to cohorts with an inflated swimbladder that exhibited an angle of 27±6°. In conclusion, there was a clear effect of high aqueous levels of CO2 and environmental temperature on growth and skeletal deformity which, in turn, affected juvenile quality in the white grouper.

Developmental toxicity, EROD, and CYP1A mRNA expression in zebrafish embryos exposed to dioxin-like PCB126.

Dioxin-like PCB126 is a persistent organic pollutant that causes a range of syndromes including developmental toxicity. Dioxins have a high affinity for aryl hydrocarbon receptor (AhR) and induce cytochrome P4501A (CYP1A). However, the role of CYP1A activity in developmental toxicity is less clear. To better understand dioxin induced developmental toxicity, we exposed zebrafish (Danio rerio) embryos to PCB126 at concentrations of 0, 16, 32, 64, and 128 μg L(-1) from 3-h post-fertilization (hpf) to 168 hpf. The embryonic survival rate decreased at 144 and 168 hpf. The fry at 96 hpf displayed gross developmental malformations, including pericardial and yolk sac edema, spinal curvature, abnormal lower jaw growth, and non-inflated swim bladder. The pericardial and yolk sac edema rate significantly increased and the heart rate declined from 96 hpf compared with the controls. PCB126 did not alter the hatching rate. To elucidate the mechanism of PCB126-induced developmental toxicity, we conducted ethoxyresorufin-O-deethylase (EROD) in vivo assay to determine CYP1A enzyme activity, and real-time PCR to study the induction of CYP1A mRNA gene expression in embryo/larval zebrafish at 24, 72, 96, and 132 hpf. In vivo EROD activity was induced by PCB126 at 16 μg L(-1) concentration as early as 72 hpf but significant increases were observed only in zebrafish exposed to 64 and 128 μg L(-1) doses (p < 0.005) at 72, 96, and 132 hpf. Induction of CYP1A mRNA expression was significantly upregulated in zebrafish exposed to 32 and 64 μg L(-1) at 24, 72, 96, and 132 hpf. Overall, the severe pericardial and yolk sac edema and reduced heart rate suggest that heart defects are a sensitive endpoint, and the general trend of dose-dependent increase in EROD activity and induction of CYP1A mRNA gene expression provide evidence that the developmental toxicity of PCB126 to zebrafish embryos is mediated by activation of AhR.

Relationship between uninflated swim bladder and skeletal anomalies in reared gilthead seabream (Sparus aurata)

Abstract The higher mortalities and lower morphological quality of juveniles with a non-inflated swim bladder still remain a major problem in intensive farming. The aim of this study was to investigate a possible relationship between the presence of an abortive swim bladder and skeleton anomalies in gilthead seabream juveniles. A batch of 109 DAH (LS range: 16–47 mm) gilthead seabream was split into two groups on the basis of the presence (SB group)/absence (WSB group) of a normally inflated swim bladder, and processed for skeletal anomaly and meristic count analysis. The presence of pectoral fin anomalies and the absence of any clear-cut and sound relationship between abortive swim bladder and axis deviations characterize the WSB group. Rarer anomalies, such as scoliosis and lordosis in the pre-haemal vertebrae, kyphosis in the haemal vertebrae, pre-haemal and haemal vertebrae body anomalies, exclusively affected the WSB seabream. This result contradicts what is observed in other species, where abortive swim bladder is shown to cause axis deviation. The authors hypothesize that when gilthead seabream larvae with uninflated swim bladder encounter difficulty in maintaining the level in the water column, they have to overuse flapping of the pectoral fins (which appear more deformed in the seabream without swim bladder of this study). This determines a hyper-activity of the pectoral muscles, which then exerts an intense mechanical load on pre-haemal muscles and ossifying vertebrae. Vertebrae and axis anomalies in the pre-haemal and in haemal (in this study still rare in the WSB lot) regions may be later effects, as postural consequences due to the uninflated swim bladder.

Prey Density and Nonvisual Feeding by Larval Striped Bass

AbstractLarvae of striped bass Morone saxatilis from the Shubenacadie River, Nova Scotia, exhibited a good nonvisual feeding mechanism that may be valuable for survival in their turbid estuarine nursery habitat. Their capture of brine shrimp Artemia salina nauplii during 60‐min feeding trials in darkness was significantly affected by the interaction between prey density and larval age. Mean capture rate among larvae that were offered 50, 200, and 800 prey/L at 9 d posthatch (dph) was 3, 7, and 15 prey·larva−1·h−1, respectively, and increased progressively with age to 26, 92, and 220 prey·larva−1·h−1 at 22 dph. By comparison, prey capture rate in the light (20 lx) among 8–13‐dph larvae that were offered 50 prey/L was about fourfold higher than the capture rate for nonvisual feeding; however, at 800 prey/L, capture rates in lighted conditions and in darkness were similar. Among larvae with noninflated swim bladders, prey capture in the dark was severely inhibited.

Evaluation of the Viability and Growth of Walleye Embryos and Larvae after Antiviral Iodine Treatment

AbstractAvoiding the transmission of viral disease and securing the health of fish populations are vital for hatchery‐based stocking programs in regions affected by viral hemorrhagic septicemia (VHS). Iodine compounds are nonselective antiviral substances that are widely used as disinfectants, but their effects on survival and growth during early life stages of fish require further study. Two groups of walleyes Sander vitreus were collected from the Maumee River (Perrysburg, Ohio) in March 2009. Group 1 (6 females and 3 males) was collected midmorning, and group 2 (10 females and 4 males) was collected that evening. Gametes were collected on site for group 1; group 2 fish were held in tanks overnight, and their gametes were collected the next morning. Gametes were transported (3–4 h) to the laboratory, where eggs from individual females were fertilized with the combined sperm of three to four males. Directly after fertilization and tannic acid treatment, embryos were exposed to iodine at 0 mg/L (control) or 100 mg/L (triplicate) for 30 min. Survival to the eyed embryo stage was estimated for both groups. Only larvae from group 1 were sampled prior to first feeding (live nauplii of brine shrimp Artemia spp.) at 9 d posthatch (dph) and approximately every 10 d thereafter until 48 dph to assess growth. Samples of eggs, ovarian fluid, larvae, and juveniles were collected for VHS testing. Survival to the eyed embryo stage for group 1 was not affected by treatment, but iodine treatment significantly decreased survival for group 2. Growth was unaffected by iodine treatment, and all samples that were tested for VHS were negative. Histological analysis of swim bladder morphology revealed that larvae with noninflated swim bladders had features of an undeveloped organ with hyperplastic epithelium consisting of vacuolarized cells. Walleye eggs that are collected according to the procedures used for group 1 can be treated with 100‐mg/L iodine for 30 min without sacrificing survival or growth in regions affected by VHS.

Developmental toxicity of dextromethorphan in zebrafish embryos/larvae

Dextromethorphan is widely used in over-the-counter cough and cold medications. Its efficacy and safety for infants and young children remains to be clarified. The present study was designed to use zebrafish as a model to investigate the potential toxicity of dextromethorphan during embryonic and larval development. Three sets of zebrafish embryos/larvae were exposed to dextromethorphan at 24, 48 and 72 h post fertilization (hpf), respectively, during the embryonic/larval development. Compared with the 48 and 72 hpf exposure sets, the embryos/larvae in the 24 hpf exposure set showed much higher mortality rates which increased in a dose-dependent manner. Bradycardia and reduced blood flow were observed for the embryos/larvae treated with increasing concentrations of dextromethorphan. Morphological effects of dextromethorphan exposure, including yolk sac and cardiac edema, craniofacial malformation, lordosis, non-inflated swim bladder and missing gill, were also more frequent and severe among zebrafish embryos/larvae exposed to dextromethorphan at 24 hpf. Whether the more frequent and severe developmental toxicity of dextromethorphan observed among the embryos/larvae in the 24 hpf exposure set, as compared with the 48 and 72 hpf exposure sets, is due to the developmental expression of the phase I and phase II enzymes involved in the metabolism of dextromethorphan remains to be clarified. A reverse transcription-polymerase chain reaction analysis, nevertheless, revealed developmental stage-dependent expression of mRNAs encoding SULT3 ST1 and SULT3 ST3, two enzymes previously shown to be capable of sulfating dextrorphan, an active metabolite of dextromethorphan.

Swimbladder condition and target strength of myctophid fish in the temperate zone of the Northwest Pacific

Abstract Yasuma, H., Sawada, K., Takao, Y., Miyashita, K., and Aoki, I. 2010. Swimbladder condition and target strength of myctophid fish in the temperate zone of the Northwest Pacific. – ICES Journal of Marine Science, 67: 135–144. We report theoretical values of the target strength (TS) of four myctophid fish (Ceratoscopelus warmingii, Myctophum asperum, Diaphus garmani, and Diaphus chrysorhynchus) based on morphometry of the swimbladder. None of the D. chrysorhynchus had an inflated swimbladder, but the other species had both inflated and non-inflated swimbladders, depending on body size. The relationships between swimbladder and body length showed that once gas production started, the swimbladders grew faster than the rest of the body (positive allometric growth). However, M. asperum showed regression of the swimbladder after positive allometric growth, so larger specimens had non-inflated swimbladders. Based on the measurements of swimbladder and body length, the theoretical TS values at 38 and 120 kHz were calculated using existing sound-scattering models. In fish with inflated swimbladders, TS values were relatively low (less than −67 dB, reduced TScm) at both frequencies. Regression slopes on TS–body length (log) plots were &gt;20, suggesting that their scattering cross sections were not proportional to the square of the body length. In contrast, the TS values of M. asperum decreased with growth in large fish (60–80 mm long) through swimbladder regression. Scattering cross sections of fish without swimbladders were not proportional to the square of the body length over the whole size range.

Genetic investigation of swimbladder inflation anomalies in the European sea bass, Dicentrarchus labrax L.

Although the aetiology of swimbladder inflation anomalies in important aquaculture species such as European sea bass D. labrax is not fully determined, culture conditions are commonly suggested as main contributory factors. Little information is available on whether swimbladder inflation has a genetic basis for its expression too. In this work, 24 full-sibling sea bass families from a 4 dams × 6 sires factorial crossing were reared under communal conditions. The larvae developing normal and abnormal (uninflated or hyper-inflated) swimbladders were genotyped at four microsatellite loci, Labrax-3, Labrax-13, Labrax-17, Labrax-29, and allocated to the individual breeders. Out of 273 offspring, 97% could be assigned to a single parental pair. The genotype and pedigree analysis showed an imbalance in family size due to differential survival of larvae with normally inflated swimbladders, with the offspring generated from one dam and one sire being two- to three-fold superior to the other parents, respectively. In larvae with non-inflated swimbladder, significant differences in family size were observed only among half-sibling sire families, whereas in larvae with hyper-inflated swimbladder such differences were found both among half-sibling sire and dam families. The results suggest that paternally and maternally inherited factors may contribute to the expression of swimbladder anomalies in sea bass along with major environmental clues.

Morphological and genetic characterization of swimbladder non-inflation in angelfish Pterophyllum scalare (Cichlidae)

Abnormal development of the swimbladder is described in angelfish, Pterophyllum scalare (Lichtenstein 1823), a popular freshwater ornamental fish widely cultured in a range of strains and varieties. Non-inflated swimbladders in some individuals became apparent when larvae reached an age of 2 weeks. Affected fish were incapable of maintaining their position in the water body and sank to the tank bottom, resting on their flanks. Swimming bouts involved arduous tail movements in an attempt to maintain their position in the water body. Affected fish had slender trunks and partly folded backward dorsal and ventral fins. Histologically, affected fish had a solid cluster of hypertrophic gas gland cells and a hyperplastic rete mirabile instead of a gas-inflated swimbladder. Although it was not determined whether atmospheric air is obligatory for initial inflation of the swimbladder in larvae of this species, the evidence presented suggests that access to the water surface for this purpose in angelfish may not be obligatory. Dilated swimbladders were observed in 1-day-old larvae that were still attached to the hatching stick or had dropped to the tank bottom, with no contact to the water surface. Larvae that had been collected from the water surface displayed similarly dilated swimbladders. The possible cause of swimbladder non-inflation in angelfish is presently under investigation. Although the aetiology remains unknown, we found some alterations in gene expression that were associated with swimbladder non-inflation. The underlying factors have yet to be determined, although genomic alterations, environmental conditions or induced mutation, which involves both factors, are suspected as contributory factors.

Sorting Eurasian perch fingerlings ( Perca fluviatilis L.) with and without functional swim bladder using tricaine methane sulfonate

A sorting method based on anaesthetic level to separate perch juveniles with and without functional swim bladder is developed. After anaesthesia, individuals with an inflated swim bladder (SB+) float whereas those without an inflated bladder (SB−) sink. An increase of tricaine methane sulfonate (TMS) from 30 to 100 mg/l reduces anaesthesia. Time to reach complete anaesthesia is also shorter in unfed fingerlings and when salinity of TMS concentration is increased. Optimal TMS concentration is about 50–70 mg/l for 20-day-old fingerlings. Sorting efficiency and survival post handling of 30-day-old fingerlings remain maximal regardless of tested anaesthetic concentration (from 30 to 100 mg/l). Juveniles need to remain unfed during at least 6 h before handling to prevent sorting error and increased mortality levels, among SB+ and SB− 25-day-old fingerlings. Adding sea salt with anaesthetic solution significantly improves sorting efficiency. Minimum salt concentration reaches 20 g/l for 20- and 25-day-old fingerlings, whereas 10 g/l suffices for 30-day-old fingerlings. Fingerlings measuring 15–16 mm (20–25 days post hatch) are more sensitive to changes in salinity and handling than both larger and smaller individuals. We propose the hypothesis that weakness of this fingerling category could be attributed to morphologic or physiologic changes. In 86% of studied batches, inflated swim bladder fingerlings grow better than non-inflated swim bladder fingerlings. In husbandry conditions, this growth difference leads to size dispersion and losses caused by cannibalism. Regarding swim bladder inflation state, early sorting is a means to maintain homogeneity of juvenile populations. This procedure is recommended for fingerlings batches where swim bladder inflation failed excessively.

Effects of light intensity, tank colour and photoperiod on swimbladder inflation success in larval striped bass, Morone saxatilis (Walbaum)

Striped bass, Morone saxatilis (Walbaum), larvae, although physoclistous as adults, initially need to inflate their swimbladders by passing ingested air through a pneumatic duct to the swimbladder. Failure to inflate the swimbladder results in swimbladder atrophy, dysfunctional buoyancy control, deformities, and poor larval survival and growth. The present investigation studied the effects of light intensity, tank colour and photoperiod on the initial swimbladder inflation success of striped bass. In the first experiment, newly hatched larvae were reared for 2 weeks in black or white 350-L circular tanks exposed to incandescent lighting at 163 or 10 lux. Larvae were fed Artemia from 6 days post-hatching (dph). The standard length, and oil globule and yolk areas were measured. Swimbladder condition and evidence of feeding were recorded. To study the effects of photoperiod on inflation, larvae were reared in black tanks exposed to either 8 h:16 h or 16 h:8 h light:dark photoperiods at 139 lux. Striped bass inflated their swimbladders between 6 and 9 dph at 17 oC. Inflation success was significantly higher in black tanks (65%) compared with white tanks (42%), but light intensity did not significantly affect swimbladder inflation. Larval growth and food consumption were better in black tanks, primarily because this treatment resulted in more larvae with inflated swimbladders, although larvae with uninflated swimbladders in black tanks were longer at 12 dph than larvae with inflated swimbladders in white tanks. Larvae that successfully inflated their swimbladders fed earlier and exhibited better growth than larvae with noninflated swimbladders. Larvae reared at higher light intensities used up yolk reserves faster. Exposing striped bass larvae to 8 h:16 h light:dark photoperiods resulted in higher inflation rates (55%) compared to larvae reared at 16 h:8 h light:dark photoperiods (30%). Therefore, black tanks and short photoperiods are preferable for early rearing of striped bass larvae to maximize swimbladder inflation success.

Histological Investigation of Swim-bladder Morphology and Inflation in Cultured Larval Striped Trumpeter (Latris lineata) (Teleostei, Latridae)

Histological techniques revealed that primary swim-bladder inflation in Latris lineata, a Tasmanian marine finfish, occurred before first feeding (Days 6 to 8 after hatch, depending on culture conditions). The histological appearance of the swim-bladder altered markedly after inflation; the lumen lining changed from columnar epithelium to predominantly squamous epithelium with an anterior crescent of cuboidal epithelial cells forming the gas gland. The pneumatic duct traversed ventrally from the posterior end of the swim-bladder and entered the intestine at the junction of the oesophagus and the intestine. The columnar epithelium persisted in non-inflated swim-bladders, and proliferation of the underlying vascular system caused the epithelium to fold and fill the entire lumen.

Histopathology of swimbladder noninflation in walleye ( Stizostedion vitreum) larvae: role of development and inflammation

Noninflation of the swimbladder is a major obstacle in culture of many fish larvae including walleye ( Stizostedion vitreum). 79 walleye larvae, 4–19 days posthatch, were serially sectioned for histologic study of swimbladder development. All walleye had a swimbladder and vascular rete. Inflation of the swimbladder began at 6 days posthatch, coinciding with the time of yolk sac depletion and initiation of feeding. From 7 to 11 days posthatch, macrophages infiltrated 11 of 18 (61%) noninflated and 3 of 16 (19%) inflated swimbladders. From 12 to 19 days posthatch, macrophages infiltrated 16 of 16 (100%) noninflated and 0 of 14 (0%) inflated swimbladders. Organic debris and large numbers of bacterial rods filled the noninflated swimbladder of a 13 day old larvae examined by electron microscopy. In larvae with noninflated swimbladders, the pneumatic duct was patent and its diameter remained fairly constant (25–45 μm) through 19 day posthatch, but the pneumatic duct atrophied in larvae with inflated swimbladders. During the interval of swimbladder inflation, 6–12 day posthatch, ostia of the common bile duct and pneumatic duct occupied the same lumen of the undifferentiated foregut; we hypothesize that surfactant-like secretions from the common bile duct affected fragmentation of large ingested air bubbles for transfer into the relatively small-diameter pneumatic duct. After 12 day posthatch, however, the pyloric sphincter developed and separated the common bile duct in the intestine from the pneumatic duct in the dorsal wall of the stomach. We conclude that swimbladder noninflation in walleye results from ingestion of bacteria and organic debris into the swimbladder 6–11 day posthatch, and that differentiation of the foregut prevents inflation after 12 day posthatch.

Occurrence of inflated swimbladders in five species of lanternfishes (family Myctophidae) from waters off southern California

The swimbladders of three species of myctophid fishes (Symbolophorus californiensis, Tarletonbeania crenularis and Diaphus theta, collected in the Southern California Bight between 1963 and 1978), previously observed to have both inflated and noninflated swimbladders as adults, were examined to determine if the swimbladders either vary in their inflation on a diel basis or cease to be inflated and possibly become nonfunctional in some individuals. The swimbladders of two lanternfishes reported to lack inflated swimbladders as adults (Lampanyctus regalis and L. ritteri) were included in the study for comparison. Only the swimbladder of L. regalis did not increase in size with increasing fish size. In the remaining four species, both the lengths and volumes of noninflated swimbladders were positively correlated with fish standard length (SL). Although the swimbladder continued to increase in size, inflated swimbladders were not found in L. ritteri>2 mm SL. Inflated and noninflated swimbladders occurred in overlapping size ranges of S. californiensis, T. crenularis, and D. theta. Only 11% of the D. theta swimbladders were inflated, and the occurrence of inflated swimbladders dit not differ significantly with day vs night capture or fish size. Although the frequency of occurrence of inflated swimbladders decreased significantly in larger S. californiensis, both S. californiensis and T. crenularis caught at the surface at night with a neuston net had significantly higher proportions of inflated swimbladders than did those collected below the surface with either daytime or night-time trawls. The swimbladder does not appear to become nonfunctional in either species. Rather than maintaining either constant volumes or constant masses of gas in their swimbladders during their vertical migrations, both species may inflate their swimbladders only while in the surface waters at night, and have noninflated swimbladders while at other depths of their vertical ranges.