Molecular characterization of the fish-pathogenic fungus Aphanomyces invadans

Aphanomyces invadans (Saprolegniaceae) is a peronosporomycete fungus associated with the serious fish disease, epizootic ulcerative syndrome (EUS), also known as mycotic granulomatosis. In this study, interspecific relationships were examined between A. invadans isolates and other aquatic animal pathogenic Saprolegniaceae, and saprophytic Saprolegniaceae from EUS-affected areas. Restriction fragment length polymorphisms and sequences of ribosomal DNA confirmed that A. invadans is distinct from all other species studied. A sequence from the internal transcribed spacer region ITS1, unique to A. invadans, was used to design primers for a PCR-based diagnostic test. Intraspecific relationships were also examined by random amplification of polymorphic DNA using 20 isolates of A. invadans from six countries. The isolates showed a high degree of genetic homogeneity using 14 random ten-mer primers. This provides evidence that the fungus has spread across Asia in one relatively rapid episode, which is consistent with reports of outbreaks of EUS. Physiological distinctions between A. invadans and other Aphanomyces species based on a data set of 16 growth parameters showed remarkable taxonomic congruence with the molecular phylogeny.     

Effect of substrate on progression and healing of skin erosions and epidermal papillomas of Atlantic halibut, Hippoglossus hippoglossus (L.)

Juvenile Atlantic halibut cultured on a smooth substrate often develop skin lesions on the blind (abocular) side, significantly reducing carcass value and causing economic losses. We discovered that fish not only developed skin erosions, but also extensive epidermal papillomas when held on a smooth substrate for 39 months. This is the first time that epidermal papillomas have been reported in Atlantic halibut. To determine whether substrate type affected the progression or healing of these lesions, fish with papillomas and skin erosions were moved to identical rearing units having either an irregular (sand, gravel or Netlon) substrate, or a smooth (gel-coated fibreglass) substrate. After 62 days, 42-50% of fish held on any of the three irregular substrates had a skin erosion area (SEA) that had either diminished or appeared to be completely healed via gross examination. In contrast, none of the fish held on the smooth substrate showed improvement and 75-100% had a more severe SEA. Changes in the papilloma area (PA) were less dramatic: none of the fish held on an irregular substrate had any clear change in PA, although there was a suggestion that the PA in some fish might becoming less severe. Similarly, none of the fish held on the smooth substrate had a change in PA, although there was a suggestion that the PA in some fish was becoming more severe. After 97 days, there was also a suggestion that specific growth rates were higher in fish held on an irregular substrate when compared with those held on the smooth substrate. Overall, these data further substantiate previous studies suggesting that an irregular substrate, including the commercially used Netlon, is best for rearing Atlantic halibut. While there was a clear relationship between substrate type and whether skin erosions or papillomas progressed or healed, the exact cause(s) of these two responses is uncertain. Future studies should focus on risk factors such as stress, burrowing behaviour and the microenvironment of the substrate.     

Mycobacteria isolated from Chesapeake Bay fish

Mycobacteriosis in fish can result in ulcers, emaciation, and in some cases death. Mycobacteria have been previously isolated from a variety of Chesapeake Bay fish species, and the current study was designed to identify potential host specificity and location fidelity of mycobacterial isolates. Mycobacteria were isolated from wild fish of the Chesapeake Bay collected from the Upper Bay, the Choptank River, Herring Bay, the Chicamacomico River, the Pocomoke River and the Potomac River in 2003–2006. Mycobacterial isolates were recovered from striped bass, Morone saxatilis , Atlantic menhaden, Brevoortia tyrannus , white perch, Morone americana , summer flounder, Paralichthys dentatus , spot, Leiostomus xanthurus , largemouth bass, Micropterus salmoides , channel catfish, Ictalurus punctatus , common carp, Cyprinus carpio carpio , spotted seatrout, Cynoscion nebulosus , killifish, Fundulus sp., blueback herring, Alosa aestivalis , American gizzard shad, Dorosoma cepedianum and American silver perch, Bairdiella chrysoura . Twenty-nine well-defined mycobacterial groups resulted from gas chromatography dendrogram clustering of isolates. The majority of groups included more than one host species and more than one site of collection. However, four groups contained only striped bass isolates, three of which were similar to M. shottsii . Therefore, multiple Chesapeake Bay fish species are colonized with multiple mycobacterial isolates, of which few appear to be host or location specific.     

Atlantic coast feeding habits of striped bass: a synthesis supporting a coast-wide understanding of trophic biology

The recent increase in the Atlantic coast population of striped bass, Morone saxatilis (Walbaum), prompted managers to re‐evaluate their predatory impact. Published and unpublished diet data for striped bass on the Atlantic Coast of North America were examined for geographical, ontogenetic and seasonal patterns in the diet and to assess diet for this species. Diets of young‐of‐the‐year (YOY) striped bass were similar across the Upper Atlantic (UPATL), Chesapeake and Delaware Bays (CBDEL) and North Carolina (NCARO) areas of the Atlantic coast where either fish or mysid shrimp dominate the diet. For age one and older striped bass, cluster analysis partitioned diets based on predominance of either Atlantic menhaden, Brevoortia tyrannus (Latrobe), characteristic of striped bass from the CBDEL and NCARO regions, or non‐menhaden fishes or invertebrates, characteristic of fish from the UPATL, in the diet. The predominance of invertebrates in the diets of striped bass in the UPATL region can be attributed to the absence of several important species groups in Northern waters, particularly sciaenid fishes, and to the sporadic occurrences of Atlantic menhaden to UPATL waters. In all regions, across most seasons and in most size classes of striped bass, the clupeiod fishes; menhaden, anchovies (Anchoa spp.) and river herrings (Alosa spp,) and Atlantic herring, Clupea harengus L., dominated the diets of striped bass above the first year of life.     

Predator–prey analysis of striped bass and Atlantic menhaden in upper Chesapeake Bay

Between 1997 and 2000, an outbreak of skin lesions and observations of emaciated striped bass, Morone saxatilis (Walbaum), in upper Chesapeake Bay were attributed to a perceived shortage of its main prey, Atlantic menhaden, Brevoortia tyrannus Latrobe. Abundance estimates, Atlantic menhaden consumption per recruit analysis (modified yield‐per‐recruit), bioenergetics analysis and predator–prey theory were combined to explore whether an imbalance between striped bass and Atlantic menhaden in upper Chesapeake Bay was plausible. Reduced fishing mortality and higher size limits that underpinned the effort to restore striped bass during the 1980s and 1990s lead to more abundant and larger striped bass in upper Chesapeake Bay, increasing predatory demand for forage‐sized Atlantic menhaden, the abundance of which declined to a historic low. Nominal losses of age 0–2 Atlantic menhaden to harvest and potential striped bass predation exceeded supply after 1998. The outbreak of lesions in upper Chesapeake Bay striped bass coincided with increased variation in weight‐at‐length, decreased length‐at‐age, and decreased presence of Atlantic menhaden in diets. Decreased attack success, inferred from a 97% decline in ratios of forage‐sized Atlantic menhaden to striped bass between 1983 and 1998, would have expected to have been followed by a deterioration of striped bass nutritional state. Transmission of disease would have been aided by high density of striped bass in poor nutritional condition residing in degraded habitat (Chesapeake Bay was the most hypoxic estuary in the mid‐Atlantic region in the late 1990s). These problems suggest that striped bass exceeded their carrying capacity in Chesapeake Bay during the late 1990s.     

The effect of dietary vitamin K (phylloquinone and menadione) levels on the vertebral formation in mummichog Fundulus heteroclitus

SUMMARY: The effect of different dosages of vitamin K, either as phylloquinone or menadione sodium bisulfite (MSB), on vertebrae formation during growth of mummichog Fundulus heteroclitus was investigated. Diets without vitamin K caused a significantly higher incidence of bone deformity in fish than diets supplemented with MSB or phylloquinone ( P < 0.01). These results indicate that vitamin K is essential for mummichog. A massive dose of MSB caused a high incidence of bone deformity compared with a lower dose, while an increased dose of phylloquinone brought about no significant difference in deformity incidence. The vertebral deformity was significantly higher ( P < 0.01) in fish fed a vitamin K-free diet (Control Group) and MSB-supplemented diet (Group MSB25) compared to fish fed a phylloquinone-supplemented diet (Group PK1). These results indicate that phylloquinone is more suitable than MSB as a vitamin K source in fish feed.     

The South Atlantic Bight Recruitment Experiment: introduction and overview

The South Atlantic Bight Recruitment Experiment (SABRE) brought together a interdisciplinary team of scientists to conduct research to enhance our understanding of the relationship between variation in environmental factors and the variable recruitment of 'estuarine dependent' fishes within the SAB. The project sought to develop a new fusion of government and academic scientists, each possessing unique skills, to address the difficult problem of recruitment variability in fishes. This fusion required the development of appropriate and at that time novel management and administrative strategies. SABRE initially focused on recruitment dynamics of Atlantic menhaden, Brevoortia tyrannus , in the South Atlantic Bight, but expanded over time to include several estuarine-dependent species and much of the Middle Atlantic Bight as well. The project was conducted from 1991 to 1997 and resulted in a substantial improvement in our understanding of the life history and ecology of Atlantic menhaden and the potential constraints upon its recruitment. SABRE also contributed to our understanding of the physical oceanography of the western North Atlantic shelf and adjacent coastal inlets and the implications of physical dynamics upon the potential pathways for larval transport.     

Effect of tributyltin oxide exposure on the F<Subscript>0</Subscript> and F<Subscript>1</Subscript> generations of a marine teleost,the mummichog <Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>

The effects of organotin compounds on marine organisms, especially on their reproduction, are a continuing source of concern. We performed full-life-cycle exposure tests of tributyltin oxide (TBTO) at sub-lethal concentrations (0.13, 0.25, 0.5 and 1.0 μg/l) using a marine fish, the mummichog Fundulus heteroclitus, and studied the toxic effects of exposure to TBTO at various life-cycle stages of the fish. The effect of TBTO was initially studied on sex differentiation and then on spermatogenesis in maturing fish. A mating experiment was performed to determine the effects of exposure on the fecundity of female fish, fertilization success, and the hatch of the F₁ generation. In all experimental groups, TBTO exposure resulted in a tendency toward a male-biased sex ratio and caused a significant increase in the frequency at which apoptotic cells appeared in the testes. Exposure to 1.0 μg/l TBTO resulted in a significant decrease in fecundity, but no significant effect was found on the fertilization ratio. Time to hatch and hatchability of the F₁ generation were markedly affected in some exposure groups. These results indicate that long-term exposure of the mummichog to TBTO affects not only gonadal sex differentiation and spermatogenesis but also spawning and egg quality.     

Oomycete fungi associated with ulcerative mycosis in menhaden, Brevoortia tyrannus (Latrobe)

Abstract. Deep necrotic ulcers in Atlantic menhaden, Brevoortia tyrannus (Latrobe), were consistently associated with the presence of oomycete fungi. These organisms were found in over 95% of all lesions both early and late. More than one species of fungus appears to be involved, indicating that these organisms are secondary to some other stressor. However, all characteristically elicit an atypical intense granulomatous inflammatory response and do not behave pathologically as typical oomycetes. Our observation that these fungi appear to be the only organisms consistently present in the earliest stages of the disease indicates that some non-infectious stressor may be responsible for initiating the lesions and subsequently allowing the fungi to induce this atypical response.     

The induction of laboratory-based amoebic gill disease revisited

Previous work in our laboratory defined a method of inducing laboratory‐based amoebic gill disease (AGD) in Atlantic salmon, Salmo salar L. Gills of AGD‐affected fish were scraped and the debris placed into fish‐holding systems, eliciting AGD in naïve Atlantic salmon. While this method is consistently successful in inducing AGD, variability in the kinetics and severity of infections has been observed. It is believed that the infections are influenced by inherently variable viability of post‐harvest amoeba trophozoites. Here, a new method of experimental induction of AGD is presented that redefines the infection model including the minimum infective dose. Amoebae were partially purified from the gills of AGD‐affected Atlantic salmon. Trophozoites were characterized by light microscopy and immunocytochemistry and designated Neoparamoeba sp., possibly Neoparamoeba pemaquidensis. Cells were placed into experimental infection systems ranging in concentration from 0 to 500 cells L^?1. AGD was detected by gross and histological examination in fish held in all systems inoculated with amoebae. The number of gross and histological AGD lesions per gill was proportional to the inoculating concentration of amoebae indicating that the severity of disease is a function of amoeba density in the water column. The implications of these observations are discussed in the context of the existing AGD literature base as well as Atlantic salmon farming in south‐eastern Tasmania.     

From spawning grounds to the estuary: using linked individual-based and hydrodynamic models to interpret patterns and processes in the oceanic phase of Atlantic menhaden Brevoortia tyrannus life history

Present theory suggests that population regulation in marine fishes cannot be resolved until an understanding of the processes involved in shaping the overall distribution (the number of populations, geographical extent, mean abundance and temporal changes in abundance) is developed. Here, we present a step toward understanding Atlantic menhaden population patterns, by studying processes in the Middle and South Atlantic Bights, which shape those patterns. We use individual-based and hydrodynamic models to reinterpret the 'mechanics' of the menhaden life history, and put forward several potentially testable hypotheses. The success of the menhaden reproductive strategy seems to depend on the seasonal changes in the mean flow field of the Middle and South Atlantic Bights, suggesting that their life history may have been strongly structured by the regional physics of the system. Because the annual menhaden migration is size-based and spawning occurs throughout the population's range, the size distribution of the adult population may influence the supply of larvae to particular estuaries along the coast. Recruitment of larvae into Delaware and Chesapeake Bays may be dependent on spawning to the north of the bays' mouths, owing to coastline shape and orientation in the vicinity of the bays. Our results suggest that management of this resource might be improved by consideration of the spatial and temporal variability in both the biological and the physical system.     

A continuous, underway fish egg sampler

We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with areal abundance estimated from vertically integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993–94, had a linear scale of 5–10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may be related to bathymetry. CUFES is now being used to estimate spawner biomass by the daily egg production method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sample by CUFES.     

Evidence for enhanced salinity tolerance of a suspected fungal pathogen of Atlantic menhaden, Brevoortia tyrannus Latrobe

Abstract. Two saprolegniaceous fungi, one recovered from Atlantic menhaden, Brevoortia tyrannus Latrobe, and the other from fresh water, were compared for their abilities to withstand salinity stress. Results of stress protein analyses indicated that vegetative mycelium of the isolate from menhaden was better adapted to mesohaline salinities than the freshwater isolate. Experiments testing the propagative ability of both fungi during salt exposure further suggested that the fungus recovered from menhaden was more salt tolerant and possibly survives in estuaries because of nutrients present in susceptible fish. Implications of the findings relative to the pathogenic potential of fish pathogenic saprolegniaceous fungi in estuarinc water columns are discussed.     

Comparative evaluation of heat-processed Winged bean (Psophocarpus tetragonolobus) meals as partial replacement for fish meal in diets for the African catfish (Clarias gariepinus)

Mature winged bean (Psophocarpus tetragonolobus) (cultivar Tpt26) seeds were roasted or autoclaved and their meals evaluated as a dietary protein source for the African catfish. Five dry practical diets (400 g protein/kg and 17.5 kJ gross energy/g dry diet) containing menhaden fish meal or each of the heat-processed winged bean meals as partial replacement (80%), (with or without 5 g -methionine/kg diet supplementation) for menhaden fish meal, were prepared and fed to triplicate groups of catfish fingerlings (5.8±1.2 g) to satiation for 70 days. No mortality occurred throughout the study and satisfactory diet acceptance was observed when the heat-processed winged bean meals replaced menhaden fish meal. Differences were found in weight gain, specific growth rate, feed and protein efficiency ratios, but were not significant (P>0.05). Digestibility of crude protein and gross energy content of the diets were high (>85%) and comparable to that of menhaden fish meal. Carcass composition of catfish did not vary significantly (P>0.05) between diet treatments. Results indicate that both autoclaved and roasted winged bean meals were acceptable as protein sources and can replace 80% of menhaden fish meal in catfish diets.     

Effects of dietary lipid and environmental salinity on growth,body composition,and cold tolerance of juvenile red drum (Sciaenops ocellatus)

Simultaneous, 6-week feeding trials were conducted in which diets containing menhaden, corn, coconut and hydrogenated menhaden oil at 7.0%, plus a diet containing 14% menhaden oil, were fed to triplicate groups of juvenile red drum (Sciaenops ocellatus) at two different salinities (5 and 32%.). Weight gain was significantly (p < 0.05) affected by diet and salinity. Fish fed the diet containing 14% menhaden oil had the greatest weight gain; whereas, fish fed the diet containing coconut oil gained the least weight. Fish in brackish water had significantly greater weight gain than fish in full-strength seawater over the 6-week period, although fish fed coconut and saturated menhaden oil in brackish water had reduced survival. Dietary lipid also significantly affected muscle and liver total lipid, hepatosomatic index (HSI), and intraperitoneal fat (IPF) ratio, as fish fed the diets containing 14% menhaden oil had higher values for all of these body condition indices.After the feeding trial, fish were subjected to a chronic cold tolerance assay. In the chronic trial, where temperature was gradually reduced over a 3-week period, fish fed the diets containing menhaden oil had significantly lower median lethal temperatures (MLT) than those fish fed the diets containing coconut, corn and saturated menhaden oils. No significant effects of cold exposure were observed on muscle and liver total lipid. Cold exposure prompted a modification in lipid metabolism by lowering total saturated fatty acids and raising (n – 3) highly unsaturated fatty acids (HUFA) in the neutral lipid of liver. Fish with the lowest MLT in the chronic assay exhibited signs of conserving (n – 3) HUFA and depleting (n – 6) fatty acids [primarily 18:2 (n – 6)], resulting in higher (n – 3)/(n – 6) ratios in the polar lipid of liver. These data suggest that the lower lethal temperature of juvenile red drum can be reduced through dietary manipulation involving the inclusion of high levels of dietary lipid rich in (n – 3) HUFA.     

Atlantic menhaden recruitment to a southern estuary: defining potential spawning regions

Atlantic menhaden ( Brevoortia tyrannus ) is an estuarine-dependent fish that spawns in coastal waters of the Middle and South Atlantic Bights. Circulation modelling studies of larval transport suggest that recruitment of larvae into the Albemarle-Pamlico Estuarine System, North Carolina, is linked to dynamics on the shelf from New York to South Carolina. Field-collected menhaden egg data (from MARMAP and SABRE) define a range of temperatures within which menhaden eggs have been found. In this study we refine the transport model-predicted spawning grounds for the 1994–95 season by using satellite-derived sea surface temperature data to highlight regions that are outside the observed spawning temperature range. We also use transport pathways leading from source locations to the estuarine system to characterize the temperature field experienced by particles/larvae during their spawning-ground to inlet transit. The modelled nearshore location of source regions agrees well with MARMAP and SABRE egg data, and points to the importance of understanding biological and physical linkages between the Middle and South Atlantic Bights. The combination of modelled transport and synoptic temperature maps can provide useful guidance to future sampling efforts as well as help refine our understanding of menhaden ecology.     

Ecosystem‐based forecasts of recruitment in two menhaden species

Gulf (Brevoortia patronus, Clupeidae) and Atlantic menhaden (Brevoortia tyrannus, Clupeidae) support large fisheries that have shown substantial variability over several decades, in part, due to dependence on annual recruitment. Nevertheless, traditional stock–recruitment relationships lack predictive power for these stocks. Current management of Atlantic menhaden explicitly treats recruitment as a random process. However, traditional methods for understanding recruitment variability carry the very specific hypothesis that the effect of adult biomass on subsequent recruitment occurs independently of other ecosystem factors such as food availability and predation. Here, we evaluate the predictability of menhaden recruitment using a model‐free approach that is not restricted by these strong assumptions. We find that menhaden recruitment is predictable, but only when allowing for interdependence of stock with other ecological factors. Moreover, while the analysis confirms the presence of environmental effects, the environment alone does not readily account for the complexity of menhaden recruitment dynamics. The findings set the stage for revisiting recruitment prediction in management and serve as an instructive example in the ongoing debate about how to best treat and understand recruitment variability across species and fisheries.     

The diet of Chesapeake Bay striped bass in the late 1950s

The diet of Chesapeake Bay striped bass, (Morone saxatilis) Walbaum, based on unpublished stomach content data from 916 fish collected between 1955 and 1959 was described. The diet in the late 1950s, quantified using an index of relative importance (IRI), was dominated by Atlantic menhaden, Brevoortia tyrannus Latrobe. Atlantic menhaden (66%) and bay anchovy, Anchoa mitchilli Valenciennes, (19%) had the highest IRI value overall. Small striped bass (<600 mm total length) ate predominantly bay anchovy (IRI = 67%). Large striped bass (≥ 600 mm total length) ate predominantly Atlantic menhaden (IRI = 93%). Since 1990 small striped bass rely more on invertebrate prey and larger fish now rely more on small pelagic prey, such as bay anchovy and 0‐age clupeids. Analysis of historical data using current techniques provided a valuable tool for comparison to help in understanding the current striped bass predator–prey relationship in Chesapeake Bay.     

Rodlet cells in Murray cod,Maccullochella peelii peelii (Mitchell), affected with chronic ulcerative dermatopathy

We have previously identified an unknown cell type in the gills of Murray cod affected with chronic ulcerative dermatopathy (CUD), a condition that causes severe erosion of epidermis surrounding cephalic and lateral line sensory canals. The condition arises in aquaculture facilities that utilize groundwater, with the cause of the condition suggested to be an unknown contaminant(s). Light and transmission electron microscopy were used to characterize and quantify the unknown cells in CUD‐affected Murray cod. The cells were identified as rodlet cells and were characterized by their oval or round shape, basally located nucleus, thick fibrillar capsule surrounding the cell, and multiple rodlet sacs containing a central electron‐dense core within the cell. Rodlet cells were present in the gills, kidney and intestine of non‐CUD‐affected and CUD‐affected Murray cod; however, differences in the numbers were observed between the groups of fish. A significantly greater number of rodlet cells were observed in the gills and collecting ducts of CUD‐affected fish. This is the first report of rodlet cells in Murray cod, and we suggest that the increased rodlet cell numbers in CUD‐affected Murray cod may be in response to unknown water contaminant(s) present in the groundwater that give rise to CUD.     

First record of epizootic ulcerative syndrome from the Upper Congo catchment: An outbreak in the Bangweulu swamps,Zambia

We report on the first outbreak of epizootic ulcerative syndrome (EUS) amongst wild fish populations in the Bangweulu swamps, an inland delta, in the north of Zambia during 2014. The area supports a large and diverse fish fauna related to, but distinct from, that of the Zambezi River system where EUS outbreaks have occurred since 2006. A sizeable artisanal fishery, based on extensive fish weirs, is sustained by the annual flooding of the swamps, and observations of the disease outbreak by fishermen were recorded. Signs typical of infection with Aphanomyces invadans were observed in a number of species. Clinical observations, histology and molecular diagnostic methods were used to confirm infection with A. invadans in two of the most commonly and severely affected species. Several features of the wetland may have contributed to the outbreak and the annual recurrence of the disease. Modes by which the disease may have been introduced into the swamps are discussed. The outbreak is of great significance as the Bangweulu swamps drain into the Congo River in neighbouring Democratic Republic of Congo, Africa's largest drainage system with an extensive and diverse fish fauna previously unaffected by EUS.