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Abstract Background The family Batrachoididae are a group of ecologically important teleost fishes with unique life histories, behavior, and physiology that has made them popular model organisms. Batrachoididae remain understudied in the realm of genomics, with only four reference genome assemblies available for the family, with three being highly fragmented and not up to current assembly standards. Among these is the Gulf toadfish, Opsanus beta, a model organism for serotonin physiology which has recently been bred in captivity. Results Here we present a new, de novo genome and transcriptome assemblies for the Gulf toadfish using PacBio long read technology. The genome size of the final assembly is 2.1 gigabases, which is among the largest teleost genomes. This new assembly improves significantly upon the currently available reference for Opsanus beta with a final scaffold count of 62, of which 23 are chromosome scale, an N50 of 98,402,768, and a BUSCO completeness score of 97.3%. Annotation with ab initio and transcriptome-based methods generated 41,076 gene models. The genome is highly repetitive, with ~ 70% of the genome composed of simple repeats and transposable elements. Satellite DNA analysis identified potential telomeric and centromeric regions. Conclusions This improved assembly represents a valuable resource for future research using this important model organism and to teleost genomics more broadly.

Background: The family Batrachoididae are a group of ecologically important teleost fishes with unique life histories, behavior, and physiology that has made them popular model organisms. Batrachoididae remain understudied in the realm of genomics, with only four reference genome assemblies available for the family, with three being highly fragmented and not up to current assembly standards. Among these is the Gulf toadfish, Opsanus beta, a model organism for serotonin physiology which has recently been bred in captivity. Results: Here we present a new, de novo genome and transcriptome assemblies for the Gulf toadfish using PacBio long read technology. The genome size of the final assembly is 2.1 gigabases, which is among the largest teleost genomes. This new assembly improves significantly upon the currently available reference for Opsanus beta with a final scaffold count of 62, of which 23 are chromosome scale, an N50 of 98,402,768, and a BUSCO completeness score of 97.3%. Annotation with ab initio and transcriptome-based methods generated 41,076 gene models. The genome is highly repetitive, with ~ 70% of the genome composed of simple repeats and transposable elements. Satellite DNA analysis identified potential telomeric and centromeric regions. Conclusions: This improved assembly represents a valuable resource for future research using this important model organism and to teleost genomics more broadly. [ABSTRACT FROM AUTHOR]

The environments in which offspring are reared can profoundly affect their development, growth, and survival. Certain specialized fish species deposit and sometimes care for their young in one of the Earth's most dynamic ecosystems: the marine intertidal zone. This tendency to deposit eggs in intertidal habitats rather than more stable coastal waters suggests intertidal conditions confer benefits to offspring that outweigh the risks parents face when spawning at the ocean's edge. Depositing eggs in the warmer intertidal zone might allow fish to produce and hatch larger eggs than would be possible in cooler subtidal waters, where development rates are much slower. We used two laboratory experiments and a field experiment to investigate how the benefits of intertidal development could vary according to egg size in the plainfin midshipman toadfish, Porichthys notatus. These toadfish breed along an intertidal gradient and down into shallow subtidal waters. We found that larger toadfish mothers produced larger eggs that hatched into larger young. Mothers laying these larger eggs also deposited them in warmer nests at higher tidal elevations, where the eggs can hatch into the largest juveniles with the highest survival rates. Juveniles that were raised in warm water in the laboratory (mimicking conditions in the high intertidal zone) experienced the highest survival rates during development and were also bolder and exhibited faster swimming speeds when fleeing a simulated predator. Taken together, these results suggest variation in propagule size can support divergent nest site choices among females, with females producing larger eggs benefiting more from depositing their eggs in warmer areas. Individual variation in propagule size could thus support niche partitioning by expanding the range of suitable conditions for nesting sites. [ABSTRACT FROM AUTHOR]

ABSTRACT Venomous fish are commonly found in Brazilian waters. The most important marine venomous fish species are stingrays (Dasyatidae, Gimnuridae, Myliobatidae, and Rhinopteridae families), catfish (Ariidae family), scorpionfish and lionfish (both Scorpaenidae family), and toadfish (Batrachoididae family). Meanwhile, Potamotrygonidae stingrays and Pimelodidae catfish are the most important venomous freshwater fish. The mechanisms of envenomation vary and involve various venomous apparatuses and glands. Despite not being highly developed, these venomous apparatuses in fish appear rudimentary, using structures such as fins and rays to inoculate toxins and rarely presenting with specialized structures. Toxins are produced by glandular tissue made up of proteinaceous cells, lacking true glands, and are positioned along the inoculation structures. However, systemic manifestations are rare. No antivenom serum has been developed for any species of American venomous fish. Brazilian venomous fish and their venoms have only recently attracted attention, leading to new studies not only addressing clinical issues in humans, but also exploring the discovery of new active substances with immense pharmacological potential.

The kidney of fish contains numerous nephrons, each of which is divided into the renal corpuscle and renal tubules. This glomerular structure is the filtration unit of the nephron and is important for the kidney function, but it has been reported that the renal corpuscle was lost in at least four independent linages of fish (i.e., aglomerular kidney). In this study, the authors newly described renal structures for three species by histological and ultrastructural observations: two aglomerular kidneys from a seahorse Hippocampus barbouri and a toadfish Allenbatrachus grunniens and a glomerular kidney from a snake eel Pisodonophis boro. The renal development of H. barbouri was also described during 1–35 days after birth. In all species tested, the anterior kidney was comprised of haematopoietic tissues and a few renal tubules, whereas the posterior kidney contained more renal tubules. Although the glomerular structure was present in P. boro, light microscopic observations identified no glomeruli in the kidney of H. barbouri and A. grunniens. Ultrastructurally, abundant deep basal infoldings with mitochondria in the renal tubules were observed in A. grunniens compared to H. barbouri and P. boro, suggesting the possible role of basal infoldings in maintaining the osmotic balance. By integrating the results from the three species and comprehensive literature search, the authors further showed that 56 species have been reported to be aglomerular, and that the aglomerular kidney has evolved at least eight times in bony fishes. [ABSTRACT FROM AUTHOR]

The morphology, histology and histochemistry of the digestive system and gut content of the wild-grunting toadfish (Allenbatrachus grunniens) from the estuary of Pranburi River, Thailand, is investigated. The digestive system of A. grunniens is elongated from the oral cavity to the intestine except for the stomach of a sac-shaped type. The length of the elongated intestine has the intestine coefficient (IC) of 0.52 ± 0.1. The digestive tract is composed of four layers: mucosa, submucosa, muscularis and serosa. The longitudinal folds of the esophagus are lined by the stratified mucosal epithelium which contains several large secretory cells. The gastric rugae in both the cardiac and pyloric regions of the stomach are lined with a simple columnar epithelium. The intestine has numerous intestinal folds lined by simple columnar epithelia. Intestinal goblet cells are organised and inserted among the epithelia. The index of relative importance (IRI) suggests that the main food items are a crab group (73.64%) followed by shrimps (10.43%), fishes (8.02%) and other compositions (7.92%). The IC, morphohistological features of the digestive system and IRI indicate that A. grunniens is a carnivorous fish. [ABSTRACT FROM AUTHOR]

Abstract Vessel‐related noise is a potential stressor for coral reef fauna. The Parque Nacional Arrecifes de Cozumel (PNAC) is a Mexican Marine Protected Area that is exposed to pervasive vessel traffic. PNAC is also the primary range of splendid toadfish (Sanopus splendidus, family Batrachoididae), an IUCN red‐listed soniferous fish for which vessel noise may represent a threat. We conducted a passive acoustic monitoring survey during summer of 2017 at Paraiso Reef in PNAC and obtained the first scientific recordings from splendid toadfish, enabling a vocal characterization of the species. We simultaneously collected data on sound levels of vessels passing near the reef. High noise levels of cruise ship and small motorboat traffic caused elevated anthropogenic sound pressure levels for up to 15 hr per day in the same bandwidth as toadfish vocalizations. A single cruise ship added up to 4 dB above nighttime ambient levels while small motorboat traffic added up to 7 dB. The overlap of toadfish vocalizations and vessel‐related noise highlights the susceptibility of splendid toadfish to acoustic masking and reduction in communication space throughout the day, warranting further study. Because acoustic communication is critical to toadfish reproductive success, noise from cruise ships and small motorboats may threaten splendid toadfish individuals or population viability.

Precise neuronal firing is especially important for behaviors highly dependent on the correct sequencing and timing of muscle activity patterns, such as acoustic signaling. Acoustic signaling is an important communication modality for vertebrates, including many teleost fishes. Toadfishes are well known to exhibit high temporal fidelity in synchronous motoneuron firing within a hindbrain network directly determining the temporal structure of natural calls. Here, we investigated how these motoneurons maintain synchronous activation. We show that pronounced temporal precision in population-level motoneuronal firing depends on gap junction-mediated, glycinergic inhibition that generates a period of reduced probability of motoneuron activation. Super-resolution microscopy confirms glycinergic release sites formed by a subset of adjacent premotoneurons contacting motoneuron somata and dendrites. In aggregate, the evidence supports the hypothesis that gap junction-mediated, glycinergic inhibition provides a timing mechanism for achieving synchrony and temporal precision in the millisecond range for rapid modulation of acoustic waveforms.

In the present study, we describe the spermatogenesis of Allenbatrachus grunniens, a benthic toadfish from Estuarine Pranburi River, Thailand, at the ultrastructural level. According to the nuclear and cytoplasmic characteristics, A. grunniens spermatogenic cells are classified into five stages. The spermatogonium contains the prominent nucleus and locates in the periphery of the seminiferous lobule. The spermatogonium develops into the primary spermatocyte and then into secondary spermatocyte, which was characterized by the dramatical increase in heterochromatin. The subsequent spermatids exhibit the centriole formation, chromatin condensation, mitochondrial redistribution, and reduced cytoplasm. After the final morphological differentiation, the spermatozoon shows an oval head with a high degree of chromatin condensation, a small midpiece consisted of prominent basal bodies surrounded by eleven mitochondria, and the biflagellate tail. Our observation demonstrates the ultrastructure of Batrachoididae spermatozoa, which can help to understand their reproductive biology. [ABSTRACT FROM AUTHOR]

Vessel‐related noise is a potential stressor for coral reef fauna. The Parque Nacional Arrecifes de Cozumel (PNAC) is a Mexican Marine Protected Area that is exposed to pervasive vessel traffic. PNAC is also the primary range of splendid toadfish (Sanopus splendidus, family Batrachoididae), an IUCN red‐listed soniferous fish for which vessel noise may represent a threat. We conducted a passive acoustic monitoring survey during summer of 2017 at Paraiso Reef in PNAC and obtained the first scientific recordings from splendid toadfish, enabling a vocal characterization of the species. We simultaneously collected data on sound levels of vessels passing near the reef. High noise levels of cruise ship and small motorboat traffic caused elevated anthropogenic sound pressure levels for up to 15 hr per day in the same bandwidth as toadfish vocalizations. A single cruise ship added up to 4 dB above nighttime ambient levels while small motorboat traffic added up to 7 dB. The overlap of toadfish vocalizations and vessel‐related noise highlights the susceptibility of splendid toadfish to acoustic masking and reduction in communication space throughout the day, warranting further study. Because acoustic communication is critical to toadfish reproductive success, noise from cruise ships and small motorboats may threaten splendid toadfish individuals or population viability. [ABSTRACT FROM AUTHOR]

The introduction of non-native predator fish is thought to have important negative effects on native prey populations. Opsanus beta is a non-native toadfish that was originally described in the Gulf of Mexico, between the west coast of Florida and Belize. In the present study, we describe, for the first time, the occurrence of O. beta in Sepetiba Bay (22°55′S), south-eastern Brazil, probably brought into the bay through ships' ballast water. Thirteen specimens were recorded in this area near to Sepetiba Port. Similarly, three other records of this species in the Brazilian coast were also reported near to port areas at Rio de Janeiro (22°49′S), Santos (23°59′S) and Paranaguá (25°33′S) ports. To confirm the species identity, we employed DNA barcoding and compared our samples with sequences deposited on public databases, which indicated that our samples are highly similar (>99.9% of genetic similarity) to O. beta samples collected near its type locality. Several individuals were found in the capable spawning phase, according to histological analysis of the reproductive cell stages. The environmental plasticity of this species and the favourable local environmental conditions probably enabled the establishment of O. beta in this region. This raises concerns of potential high invasion impact due to this species' diet and reproductive capacity. [ABSTRACT FROM AUTHOR]

Parental care is costly, and theory suggests that caregivers should reduce parental investment or even stop caring altogether when the costs of caring are too high or the benefits too low. Brood cannibalism is one tactic by which parents can divert investment away from current offspring and towards potentially higher-quality future offspring, but the various selective factors underlying partial brood cannibalism and their relative importance remain poorly understood. Here we used the plainfin midshipman fish, Porichthys notatus , to concurrently examine three hypotheses for partial brood cannibalism and test whether cannibalism increases when (1) parental body condition is low, (2) brood sizes are large and/or (3) brood paternity is low. To investigate these predictions, we combine multiyear, multisite field data with genetic paternity testing and show that partial brood cannibalism is not related to low parental body condition or to large brood sizes, but rather is linked to low paternity. In particular, males that had taken over nests from other males, and were thus unrelated to the broods present in the new nests, consumed the largest number of young (∼15 or more eaten at a time). Our data also suggest that the consumption of only a few young (∼1–2 at a time) appears to be governed by other factors that are not clearly related to paternity. Overall, we highlight the utility of concurrently testing multiple hypotheses for partial brood cannibalism within the same system to better understand this otherwise puzzling behaviour. • We tested three hypotheses for partial brood cannibalism in a wild toadfish. • Caregiving males in better body condition cannibalized more young. • The number of young cannibalized did not vary with overall brood size. • Males cannibalized the most when they were unrelated to the offspring in their nest. • Cannibalism was linked to males taking over nests (and young) from other males. [ABSTRACT FROM AUTHOR]

Nest site selection is a critical parental decision with profound fitness consequences, yet the physiological consequences of these decisions are rarely examined. Certain fishes and other aquatic organisms construct nests and provide parental care in the intertidal zone—an environment characterized by fluctuating water levels, which can exert intermittent and sometimes extreme abiotic stress on the animals that live there including dramatic changes in temperature and dissolved oxygen level. In this study, we used the plainfin midshipman fish, Porichthys notatus, to test whether (1) nest site preferences and reproductive success vary across an intertidal elevation gradient, and (2) fish that nest at higher elevations pay greater physiological costs due to prolonged exposure to more extreme abiotic conditions. We found that fish preferred nests lower in the intertidal zone, with larger males outcompeting smaller males for these sites. Broods at high elevations suffered greater offspring mortality than broods at lower elevations. The average microhabitat temperature of nests was also warmer and more variable at higher elevations compared to lower elevations. While isolated from the ocean during low tides, care-giving parents increased their use of anaerobic metabolism, and potentially draw upon oxygen reserves in the swim bladder. Our results suggest that the choice of nesting location can have profound effects on a parent's physiology and may generate significant variation in reproductive success among individuals. [ABSTRACT FROM AUTHOR]

The soundscapes of many coastal habitats include vocalizations produced by species of the family Batrachoididae (toadfish and midshipman). We describe the calling and grunting behavior of male Amphichthys cryptocentrus, a tropical toadfish, and predict how these vocalizations are influenced by conspecifics. We recorded individual males, which produced broadband grunts and multi-note, harmonic “boatwhistle” calls. Grunts were either in combination with calls or stand-alone. We used a null model to test if these latter grunts were produced at random or in response to calls from conspecifics. The model supports the hypothesis that grunts were in response to calls from neighboring males, suggesting acoustic competition. Using the most conservative estimate of hearing abilities we predict that males responded to the second harmonic of neighbor’s calls (230 Hz) at amplitudes of approximately 100-125 dB re 1μPa2/Hz. We also observed that call and grunt rates increased when males were exposed to higher rates of acoustic activity from neighboring fish. Fish used grunts to respond to background calls that occurred at different amplitudes, suggesting they responded to the calls of multiple neighboring fish and not just the highest amplitude neighbor. This communication with multiple fish within hearing range suggests a communication network in which the spatial distribution of individual toadfish relative to one another will impact their vocal behavior. Thus, the density and distribution, and not just abundance, of these toadfish at a given site will influence the characteristics of the chorus and the role of this species in the local soundscape. [ABSTRACT FROM AUTHOR]

Toadfishes (family Batrachoididae) are a well-studied family of soniferous fishes, yet only a fraction of species within the family have been recorded, and only few detailed descriptions of calls exist. Here, we present the first description of the acoustic ecology of Amphyichtys cryptocentrus, a new-world toadfish species, distributed across the southern Caribbean Sea. We recorded fourteen individuals in a seagrass habitat over six nights in the Bocas del Toro Archipelago. Like other toadfishes, A. cryptocentrus produces compound calls with broadband and tonal components; a typical call contains 1-2 grunts, followed by 1-2 boops (average fundamental frequency = 112 Hz, average source level = 138 dB re:1 μPa RMS). While we observed relatively low between-individual variation in frequency components, our results show that individuals can be readily identified based on their call composition and call rate. This suggests that each toadfish has an individual “voice,” which may transmit selection-linked information to females about body condition, status, or motivation to mate. We also observed that toadfish produced grunts during neighbors’ calls, a previously-described aggressive behavior called “acoustic tagging”, which can intercept a potential rival’s mating advertisement. Our findings suggest that A. cryptocentrus (and its population in Bocas del Toro, in particular) represents a useful system for the study of fish bioacoustics and behavioral ecology, and we demonstrate that acoustic communication represents a major aspect of social behavior in coral reef fishes. [ABSTRACT FROM AUTHOR]

Superfast muscles (SFMs) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFMs share excitation-contraction coupling pathway adaptations for speed, and if SFMs arose once, or from independent evolutionary events. Here, we demonstrate that to achieve rapid actomyosin crossbridge kinetics bat and songbird SFM express myosin heavy chain genes that are evolutionarily and ontologically distinct. Furthermore, we show that all known SFMs share multiple functional adaptations that minimize excitation-contraction coupling transduction times. Our results suggest that SFM evolved independently in sound-producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.

Background Chronically implanted electrodes allow monitoring neural activity from free moving animals. While a wide variety of implanted headstages, microdrives and electrodes exist for terrestrial animals, few have been developed for use with aquatic animals. New method A two axis micromanipulator was fabricated with a Formlabs 3D printer for implanting electrodes into free-swimming oyster toadfish ( Opsanus tau ). The five piece manipulator consisted of a base, body, electrode holder, manual screw drive and locking nut. The manipulator measured approximately 25 × 20 × 30 mm (l × w × h) and weighed 5.28 g after hand assembly. Results Microwire electrodes were inserted successfully with the manipulator to record high fidelity signals from the anterior lateral line nerve of the toadfish. Comparison with existing method(s) The micromanipulator allowed the chronically implanted electrodes to be repositioned numerous times to record from multiple sites and extended successful recording time in the toadfish by several days. Conclusions Three dimensional printing allowed an inexpensive (< $US 5 material), two axis micromanipulator to be printed relatively rapidly (<2 h) to successfully record from multiple sites in the anterior lateral line nerve of free-swimming toadfish. [ABSTRACT FROM AUTHOR]

Age, growth and mortality of the toadfish, Halobatrachus didactylus, were determined by examination of the whole sagittal otoliths of fish sampled in the Bay of Cádiz (southwestern Spain) from March 1999 to March 2000. A total of 844 specimens (425 males, 416 females, and 3 of indeterminate sex), ranging from 95 to 470 mm in total length were examined. Eighty-nine percent of the otoliths could be read allowing an age estimation. The opaque zone was formed between April and May coincident with the maximum reproductive peak, while the translucent zone formed mainly in summer-fall (June to December). Maximum ages for males and females were 12 and 10 years, respectively. The samples were dominated by 2- to 6-year-old specimens. Males matured at an age of approximately 2 years and females at 3 years. Fish total length and otolith radius were closely related (r2>0.80). The von Bertalanffy growth curve was used to describe growth. The parameters were derived from back-calculated length-at-age. Significant differences in the growth parameters were found between sexes (in males L∞ = 477.06 mm, K = 0.15 and t0 = -0.59; in females L∞ = 363.69 mm, K = 0.20 and t0 = -0.75). Although the growth analysis revealed that this species is slow-growing, males reached larger sizes than females. Females appeared to experience higher natural mortality rates than males.

Toadfish Halobatrachus didactylus gastric mucosa was studied using conventional and lectin histochemistry. Conventional histochemistry revealed neutral glycoconjugates predominating over acidic ones in the apical zone of both surface epithelial cells and pit cells. The neck cells contained a few neutral glycoconjugates, whereas gastric glands were negative to PAS and AB staining. Lectin histochemistry showed different oligosaccharide expression along the columnar cells. The sub-nuclear cytoplasm was stained with RCA120, SBA, HPA, GSA I-B4, GSA II, UEA I, LTA, Con A, KOH-sialidase-WGA. The Golgi zone reacted with RCA120, DBA, SBA, HPA, KOH-sialidase-WGA, GSA I-B4, GSA II, UEA I, LTA, MAL II, SNA, and showed an increase in DBA staining after KOH-sialidase treatment. The granules of the apical zone stained with PNA, UEA I, LTA and showed increased PNA reactivity after KOH-sialidase treatment. The luminal cell coat reacted with PNA, HPA, Con A, KOH-sialidase-WGA, UEA I, LTA, MAL II, SNA and KOH-sialidase-PNA. Pit cells showed a minor expression of lectin-binding sites with respect to columnar cells. Neck cells linked UEA I and LTA and gastric glands reacted with PNA, DBA, SBA, HPA, Con A, GSA I-B4, KOH-sialidase-WGA and KOH-sialidase-DBA. The results suggest that the stomach of the toadfish H. didactylus is characterised by a species-specific glycoconjugate pattern.

Gender related variation in the molecular composition of venoms and secretions have been described for some animal species, and there are some evidences that the difference in the toxin (s) profile among males and females may be related to different physiopathological effects caused by the envenomation by either gender. In order to investigate whether this same phenomenon occurs to the toadfish Thalassophryne maculosa , we have compared some biological and biochemical properties of female and male venoms. Twenty females and males were collected in deep waters of the La Restinga lagoon (Venezuela) and, after protein concentration assessed, the induction of toxic activities in mice and the biochemical properties were analyzed. Protein content is higher in males than in females, which may be associated to a higher size and weight of the male body. In vivo studies showed that mice injected with male venoms presented higher nociception when compared to those injected with female venoms, and both venoms induced migration of macrophages into the paw of mice. On the other hand, mice injected with female venoms had more paw edema and extravasation of Evans blue in peritoneal cavity than mice injected with male venoms. We observed that the female venoms had more capacity for necrosis induction when compared with male venoms. The female samples present a higher proteolytic activity then the male venom when gelatin, casein and FRETs were used as substrates. Evaluation of the venoms of females and males by SDS-PAGE and chromatographic profile showed that, at least three components (present in two peaks) are only present in males. Although the severity of the lesion, characterized by necrosis development, is related with the poisoning by female specimens, the presence of exclusive toxins in the male venoms could be associated with the largest capacity of nociception induction by this sample. [ABSTRACT FROM AUTHOR]

Batrachoidids, which include midshipman and toadfish are less known among embryologists, but are common in other fields. They are characteristic for their acoustic communication, and develop hearing and sound production while young juveniles. They lay large benthic eggs (> 5 mm) with a thick chorion and adhesive disk and slow development, which are particularly challenging for studying embryology. Here we took advantage of a classical tissue clearing technique and the OPenT open-source platform for optical tomography imaging, to image a series of embryos and larvae from 3 to 30 mm in length, which allowed detailed 3D anatomical reconstructions non-destructively. We documented some of the developmental stages (early and late in development) and the anatomy of the delicate stato-acoustic organs, swimming bladder and associated sonic muscles. Compared to other techniques accessible to developmental biology labs, OPenT provided advantages in terms of image quality, cost of operation and data throughput, allowing identification and quantitative morphometrics of organs in larvae, earlier and with higher accuracy than is possible with other imaging techniques. [ABSTRACT FROM AUTHOR]

The effects of the fishing industry on the marine environment have been studied and described over the past two decades. Trawl-netting is a common but non-selective method of fishing that often captures non-target specimens of no commercial value that are discarded at sea. We discovered an unreported threat caused by fisheries discards on seabirds attending fishing activities in Brazilian waters: choking by feeding on discarded Atlantic Midshipman (Porichthys porosissimus). Over 6 years of monitoring (2007–13), we recorded five procellariiform species—Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos), Cory's Shearwater (Calonectris diomedea), Sooty Shearwater (Ardenna grisea), Great Shearwater (Ardenna gravis) and Manx Shearwater (Puffinus puffinus)—dead on beaches with Atlantic Midshipman stuck in their throats and showing evidence of death by suffocation as a result of blockage of the airways through choking. This phenomenon has not been consistently described, and the consequences of the consumption of fishery discards by seabirds in Brazilian waters remain poorly understood. [ABSTRACT FROM AUTHOR]

Caring for offspring is energetically expensive, and when the costs of care are sufficiently high, the use of cost-reducing strategies can be favored. Such strategies may include the avoidance of nest construction through nest take-over and the restoration of depleted energy reserves through offspring cannibalism. Despite extensive theoretical and empirical work on parental care, neither the actual energetic costs of care nor the putative benefits of cost-reducing strategies have been systematically measured. Using plainfin midshipman fish, Porichthys notatus, we assessed how energy reserves of caring parents varied with duration of care, offspring cannibalism, and nest take-overs. We show that liver glycogen and lipid contents declined by 58% and 18.7%, respectively, that liver investment (measured via a hepatosomatic index) declined by 32.6%, and that muscle protein content declined by 8.8%. Other measures of body condition and energy reserves, such as hepatic glucose and adenosine triphosphate, remained stable over the extraordinarily long care period (3 months). Experimentally starved fish showed depletions of energy stores similar to caring fish. Fish that took over nests or that cannibalized eggs both had higher glycogen reserves than fish that did not adopt these strategies. These findings show that even when parental care is energetically costly, starvation may not be the dominant driving factor behind parent-offspring cannibalism. [ABSTRACT FROM AUTHOR]

For this report, we studied the conventional karyotype and the NOR-bearing chromosomes in the toadfish Halobatrachus didactylus. We found a karyotype of 46 chromosomes made up of 8 metacentric, 12 submetacentric, and 26 acrocentric elements (FN = 66). No heteromorphic sex chromosomes were observed in the species. Metacentric chromosomes were easily classified as homologous pairs according to their morphology and L/S ratio. The rest of the chromosomes could not be accurately classified as homologous pairs because differences in chromosome size and L/S ratio were too slight between adjacent pairs within a size-ranged series. A single pair of NOR-bearing chromosomes was found. Active NORs were terminally located in a submetacentric pair of chromosomes.

Karyotypes of three species of toadfish (Amphichthys cryptocentrus, Batrachoides manglae and Thalassophryne maculosa), reported here for the first time revealed diploid complements of 46 chromosomes. Karyo-evolutionary trend of these species is discussed. Based on differences in arm number, we suggest that T. maculosa possesses the most evolved karyotype among the three species, hence it would be the more recent one, followed by B. manglae and A. cryptocentrus.

The biology of Halobatrachus didactylus has received special attention during recent years because of its use as an experimental species in toxicology and cardiology experiments. The object of the present work is to supply basic information about the reproductive biology of this species. Samples were collected in Cádiz Bay between February 1999 and March 2000. A total of 901 specimens (440 females and 461 males) were examined. Sex ratio did not differ from the theoretical 1:1, except in May 1999, and February 2000. Minimum size at maturity was 191 mm total length for females and 160 mm total length for males. Approximately 50 % of the population matured at 262 mm for females and 302 mm for males. The spawning season extends from March to August, with a peak in May-June. Fecundity ranged from 227 to 1233 eggs/female, and was related to body length and weight. Length-weight relationship for the sexes differed, and showed positive allometry. The condition factor showed a minimum in the spawning season, which is interpreted as the result of mobilization of somatic energy reserves needed for reproductive development, and/or the use of reserves stored in the body as a source of energy in spawned fish, influenced by reduced feeding during this period.

In the Anthropocene, there is an intensification of ecological disturbances that can be directly or indirectly attributed to human activities. Seagrass meadows are among the most imperiled ecosystems worldwide and are particularly sensitive to anthropogenic disturbance events. In Everglades National Park, Florida, USA, ecological disturbances including widespread seagrass die offs, can in part be attributed to anthropogenic alteration of historic freshwater flow. In this study, we assess the impacts of seagrass die offs on the composition and behavior of aquatic organisms in acoustic communities at two ecologically similar sites in Florida Bay: Buoy Key, which experienced massive seagrass die off in 2015, and Little Rabbit Key, which did not. We focused on three sonic indicator species for North American estuaries and coastal ecosystems, and specifically Florida Bay: spotted seatrout (Cynoscion nebulosus , family Sciaenidae), gulf toadfish (Opsanus beta , family Batrachoididae), and snapping shrimp (Alpheus spp. and Synalpheus spp., family Alpheidae). The sounds produced by these species are collectively indicative of a broader range of ecosystem function and services – including trophic transfer and recreational fishing – and are more indicative of ecosystem functioning at varying temporal scales than any one species alone. Using a combination of automated detection and visual spectrographic analysis on passive acoustic data, we found that the occurrence of seatrout and toadfish calls and/or chorusing were significantly lower at the disturbed site than the undisturbed site, with no seatrout or toadfish breeding choruses detected at the disturbed location. At both sites, toadfish call properties exhibited a direct relationship with water temperature. Snapping shrimp snap rates were significantly lower at the disturbed site, and snap rates were positively related to temperature at the undisturbed location. Further, examination of a short-duration, pre-disturbance acoustic dataset, showed minimal differences in the acoustic occurrence of the three species at the disturbed site between 2015 immediately after the die off and 2018. These results support the hypothesis that by 2018 the disturbed site had not fully recovered from the most recent seagrass die off and that restoration efforts may still needed. Acoustic community composition and behavior may be used as a reliable indicator of ecosystem health and restoration success or efficacy. This work lays the conceptual groundwork for using acoustic communities as indicators in human altered systems to inform managers that habitats either may be approaching disturbance or may require continued restoration efforts to meet achieve recovery goals. • The composition and dynamics of the acoustic community can serve as an indicator of ecosystem recovery or restoration. • Altered acoustic communities may reveal that a habitat is still disturbed. • Incorporating acoustic behaviors extends inference toward whether species are engaging in activities indicative of normal ecosystem function. [ABSTRACT FROM AUTHOR]

Cannibalism of young is a common yet seemingly paradoxical phenomenon observed across a wide variety of taxa. Understanding this behaviour in the context of parental care remains a challenge for evolutionary biologists. A common adaptive explanation for the consumption of offspring is that it serves to increase the current or future reproductive success or survival of the cannibalistic parent by replenishing energy stores and facilitating continued care for any remaining young. Another explanation is that cannibalism may be a competitive response to cuckoldry or lowered certainty of parentage. We tested these ideas using the plainfin midshipman fish, Porichthys notatus , a species with an extended period of male-only parental care and documented offspring cannibalism. We found that the occurrence of cannibalism was not linked to the deterioration of body condition, but instead was most frequent during periods of high intrasexual competition and nest take-overs. Our results suggest that cannibalism is not driven by the energetic demands of parental care, but instead by competition among males for nests and females, and the resulting low paternity stemming from both nest take-overs and cuckoldry. [ABSTRACT FROM AUTHOR]