Atlantic Menhaden Research Articles

Dermal ulcerations and mortalities of estuarine fishes as indicators of environmental problems

Dermal ulcers appeared in young menhaden Brevoortia tyrannus in 1984. Field sampling showed dermal ulcers in this clupeid and in species of other families of fish from Delaware to Florida. Some mortalities were associated with the lesions. No definitive causative organism or process of lesion development was discovered and the disease was called Ulcer Disease Syndrome (UDS) by some investigators. Because various fungi were found in many of the sores, the disease was termed Ulcerative Mycosis (UM) by others. The epizootic waned around 1989–1990 as did political and scientific interest. Renewed attention, due to outbreaks of ulcers and mortalities of fish attributed to the toxic dinoflagellate Pfiesteria piscicida, revealed that UDS/UM had persisted in many East Coast estuaries. In North Carolina and Chesapeake's Pocomoke River, fish have died and some humans seem to have been affected. River closures resulted. The extent and nature of dinoflagellate and/or fungal involvement in ulcer epizootics of menhaden is under investigation. Unfortunately, ulcerations in other fishes are being largely ignored. Regardless of the principal causative organisms or the detailed processes involved in ulcer initiation and development and associated (?) mortalities, adverse environmental factors seem to have been involved in both epizootics.

Monitoring toxin uptake in edible fish tissues from Pfiesteria containing waters

Pfiesteria piscicida, a dinoflagellate first identified in 1988, has been implicated as a causative agent in major fish kills in estuaries of NC and the southeastern United States. A tissue culture assay for the detection and characterization of this toxin(s) has been adapted from standard in vitro bioassays. Using this assay, tissue samples taken from live fish caught during a fish kill were analyzed for the presence of toxin. No apparent effect on cell viability was observed using extracts from croaker, spot, striped mullet, mackerel or perch. Only those extracts of muscle tissue from Atlantic menhaden showed a significant effect in the bioassay. During the summer of 1998, a biweekly monitoring of tissue extracts of bluefish, croaker, pigfish, pinfish, spot, silver perch, southern flounder, summer flounder, weakfish, bay anchovy and menhaden was carried out. Data indicate that only tissue extracts from menhaden containing visible lesions showed a significant effect on the viability of cells in culture.

Effects of hypoxia on movements and behavior of selected estuarine organisms from the southeastern United States.

Hypoxia, or low dissolved oxygen, remains a common occurrence in estuarine waters as human activity in coastal areas expands. Fish kills, probably the most recognized indicator of these and other water quality problems, have significantly increased in recent years in many Southeastern United States estuaries. While entire aquatic communities are impacted by changes in available oxygen, estuarine organisms serve as appropriate indicators of these changes as they exhibit complex physiological and behavioral responses to hypoxia. The consequences of hypoxia for these species depend on their ability to detect and avoid areas of low dissolved oxygen. We conducted a series of two-way, replicated choice experiments with juvenile spot (Leiostomus xanthurus), pinfish (Lagodon rhomboides), croaker (Micropogonias undulatus), menhaden (Brevoortia tyrannus), white mullet (Mugil curema), mummichog (Fundulus heteroclitus), and brown shrimp (Penaeus aztecus) to determine their ability to detect and avoid specific levels of hypoxia. Additional data on organisms' movement patterns, aquatic surface respiration, and ventilation rates were collected. All species tested could detect and avoid 1 mgl(-1) dissolved oxygen. The hypoxia avoidance response differed among species, as some species exhibited an avoidance threshold while others exhibited a graded avoidance response. These data supply baseline information necessary to assess how some mobile estuarine organisms respond behaviorally to oxygen concentrations, and to understand how hypoxia more broadly impacts fish populations and estuarine community health.

Pfiesteria piscicida and Ulcerative Mycosis of Atlantic Menhaden-Current Status of Understanding.

Ulcerative lesions in estuarine finfish are associated with a variety of parasitic, bacterial, and fungal infectious agents as well as water quality and other abiotic stress factors. Atlantic menhaden Brevoortia tyrannus are a severely affected species typically exhibiting solitary, perianal, focal, deep, granulomatous lesions containing oomycete hyphae. Intense recent emphasis in the scientific literature and in the popular press has been placed on Pfiesteria-like dinoflagellates and their toxins as the causative agents for ulcerative finfish lesions in east coast estuaries of the United States. Dramatic descriptive terms for Pfiesteria, including "phantom," "ambush-predator" and "the cell from hell," capable of affecting humans, have appeared in scientific journals and the news media. However, there is no scientific evidence to date that supports a single, causal relationship between the presence of toxic Pfiesteria-like dinoflagellates and fish kills or the associated ulcerative lesions. This is due, at least in part, to the difficulty of maintaining toxic Pfiesteria-like dinoflagellates in clonal culture and, in part, to the presence of other microorganisms in laboratory culture systems. Further, there is at present no toxin-specific probe to identify Pfiesteria toxins in estuarine environments during fish kills, nor has Pfiesteria been isolated from fish lesions. Yet, based on the limited published scientific evidence and the popular press coverage, there have been river closures, notable economic losses, and public alarm due to Pfiesteria. Future research into agents infectious to menhaden, such as Aphanomyces (Oomycetes) and toxin-producing estuarine inhabitants like Pfiesteria, is needed. These organisms and the disease processes in which they are implicated may also serve as markers for overall estuarine condition. Control of microorganisms, including Pfiesteria, to improve finfish health in estuaries is unlikely. However, using the presence of these microorganisms and their Atlantic menhaden hosts as sentinels to help monitor water quality may be a viable approach to assist future estuarine management.

Behaviour and sensory physiology of Atlantic menhaden larvae, Brevoortia tyrannus, during horizontal transport

Atlantic menhaden, Brevoortia tyrannus, spawn on the continental shelf off North Carolina in the late fall and winter. Larvae are transported shoreward where they enter and migrate up estuaries to the juvenile habitat. In this paper, we synthesize behavioural and sensory physiological studies of the ontogeny of biological rhythms, responses to temperature, salinity and light, and swimbladder inflation and deflation of this species, to develop descriptive models of larval behaviour in ocean and estuarine areas that contribute to horizontal transport. Young (postyoke sac, <9 mm total length, TL) larvae occur primarily offshore, have an endogenous rhythm in nocturnal diel vertical migration, and are predicted to remain at depths above the pycnocline, if present, due to responses to light, temperature and salinity. They ascend in response to a salinity increase and temperature decrease, which frequently occur at the pycnocline. Intermediate age (9–17 mm TL) and older (18–27 mm TL) larvae are found in inshore and estuarine areas. They have an endogenous activity rhythm that suggests they will remain at moderate depths during the day in the ocean. At sunset, they swim up to surface to engulf air to fill their swimbladders and then sink due to inactivity and negative buoyancy. Thus, at night the majority of larvae are deeper than during the day. The swimbladder is deflated at sunrise in response to light and larvae are predicted to swim up to their daytime depth. They have the same responses to a temperature decrease and salinity increase as younger larvae, which should keep them above a pycnocline. The ascent to fill the swimbladder is not impeded by responses to temperature or salinity change. Chemical cues in ocean and estuarine waters induce different behavioural responses. Larvae use selective tidal stream transport for up‐estuary movement in which they are in the water column on rising tides at night and not abundant at other times. Larvae lack an endogenous tidal rhythm in vertical migration upon entering an estuary, and swimming during the day is reduced by light. The ascent into the water column during flood tides may be cued by the rate of increase in salinity at this time. Collectively, these behaviours contribute to feeding, predator avoidance and transport from the spawning area to the juvenile habitat.

Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina

The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden (Brevoortia tyrannus) from 3‐m depth off North Carolina in winter 1993–94 and 1994–95. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a. The maximal concentration of eggs was 346 eggs m−3. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid‐shelf fronts (17–23°C, 36.0–36.4‰). Unexpectedly, eggs were found almost exclusively in water of 20–60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modelling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favourable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.

BAROTROPIC TIDAL AND WIND‐DRIVEN LARVAL TRANSPORT IN THE VICINITY OF A BARRIER ISLAND INLET

Fish species such as Atlantic menhaden (Brevoortia tyrannus) must often transit relatively small barrier island inlets to move from their continental shelf spawning grounds to estuarine nurseries, where they spend their juvenile phase. Physical transport through these inlets is strongly influenced by tides, winds, local geometry and bathymetry, and can be very different from that occurring on the shelf. In March 1996, an extensive multidisciplinary field experiment was conducted to identify larval transport pathways in the vicinity of Beaufort Inlet, NC ( Blanton et al., 1999 ; Churchill et al., 1999 ; Forward et al., 1999 ). One of the most interesting results from the field study was significant spatial inhomogeneity in the larval catches ( Forward et al., 1999 ).This paper describes a computer modelling study of tidal and wind‐driven circulation and accompanying larval transport characteristics in the vicinity of Beaufort Inlet. Primary conclusions are as follows: (i) tidal currents are quite effective at creating net larval transport into the inlet; (ii) in the absence of wind forcing, to explain the spatial distribution of larval catches observed in the field experiment, the primary source of larvae must have been to the east of the inlet; (iii) the spring/neap cycle accounts for a variation of approximately 40% in larvae ingress; (iv) only a few wind directions enhance larvae ingress over the case of purely tidal forcing—wind blowing toward the north enhances ingress at the surface, and winds blowing toward the south and the east enhance ingress at the bottom; (v) if larvae are evenly distributed in space out‐side the inlet, then strong east wind (such as 10 m s−1) can cause larvae to move through the inlet in a way that is consistent with the larval catches in the field experiment. However, local wind records revealed that no significant eastward‐blowing winds occurred during or immediately preceding the field experiment.

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.

Transport of fish larvae through a tidal inlet

In the South‐eastern USA many species of estuarine‐dependent fishes spawn offshore and their larvae are transported into estuaries. The present study combined physical measurements and zooplankton sampling at the Beaufort Inlet (North Carolina) to determine: (i) whether fish larvae enter the estuary inlet in different horizontal sections of the tidal stream and (ii) whether larvae use selective tidal stream transport (STST) for ingress through the inlet and for movements up the estuary. Larvae of Atlantic menhaden (Brevoortia tyrannus), spot (Leistomus xanthurus), pinfish (Lagodon rhomboides), Atlantic croaker (Micropogonias undulatus), gulf flounder (Paralichthys albigutta), summer flounder (P. dentatus), and southern flounder (P. lethostigma) were sampled over two 25‐h periods (13–14 March, 25–26 March 1996) at three locations across the Beaufort Inlet and in the three main channels receiving water from different locations in the inlet. All species, except Atlantic croaker, primarily entered the inlet on the east side with up to an order of magnitude difference in abundance across the inlet from East to West. The gradient continued in the corresponding channels in the estuary. In most cases equal sizes of larvae were caught in the East and West channels of the estuary. Most larvae were caught at night. A pattern of abundance relative to tide was least evident in the inlet, but STST was evident in the estuary. At the location of greatest larval abundance (Shackleford Channel), the greatest numbers of all species of larvae were caught during rising tides at night. This relationship was not due to passive suspension, since abundance was higher during the faster nocturnal flood tide currents than during to ebb tide currents of equal magnitude. In the Shackleford Channel, southern/gulf flounder and pinfish were distributed throughout the water column during STST, but primarily at the surface. Atlantic menhaden, spot and Atlantic croaker were distributed throughout the water column, and summer flounder were near the surface.

Searching for sensitivity in the life history of Atlantic menhaden: inferences from a matrix model

We used modified Leslie matrix models to explore the life history of Atlantic menhaden (Brevoortia tyrannus). By examining the sensitivity of long‐term population growth rates to changes in vital rates, we identified those life history components which can cause large population level responses. Our models subdivide the first year of life into five stages (eggs, early larvae, late larvae, juveniles, and ‘peanuts’ or subadults), and population growth rate responds most strongly to changes in juvenile and late larval stages. The relative ranking between these stages is dependent on the magnitude of mortality during the prejuvenile stages relative to juvenile mortality. An examination of low‐level model parameters indicates that the population growth rate is influenced by the growth and mortality rates during the time when young‐of‐the‐year menhaden are gaining access to and residing in the estuaries. Sensitivity to changes in many adult metrics, such as fishing mortality, were relatively low. We conclude that a better understanding of biotic and abiotic factors that influence the late larval and juvenile stages will further our understanding of population dynamics in this species.

Larval transport during winter in the SABRE study area: results of a coupled vertical larval behaviour–three‐dimensional circulation model

A three‐dimensional circulation model was used in conjunction with larval fish vertical behaviour models to study the interaction between larval vertical distribution, advection and the outcome of larval transport along the central portion of the east coast of the United States. The circulation model was forced by tides, a northern boundary inflow, and winds. Vertical behaviour models were developed for Atlantic menhaden (Brevoortia tyrannus) and spot (Leiostomus xanthurus). The purpose of this modelling effort was to investigate the transport pathways of Atlantic menhaden and spot larvae from offshore spawning grounds to estuarine nursery habitats. The coupled circulation and behavioural model demonstrated the importance of along‐shelf transport in what is generally thought to be a ‘cross‐shelf’ problem. Cross‐shelf transport was associated with bathymetric features, such as shoals. Both physical (e.g. wind) and biological (e.g. changes in larval behaviour) events were responsible for many of the observed patterns in larval transport. Overall, larval transport was determined by circulation but was modified by larval vertical distributions.

Exchange and flux of larval fishes across the western Gulf Stream front south of Cape Hatteras, USA, in winter

To describe exchange and to frame the magnitude of the flux of larval fishes across the Gulf Stream front in winter, collections were taken on the inshore and offshore sides of the frontal zone in 1991, 1993, 1994 and 1995, off Onslow Bay, North Carolina. Collections yielded larval fishes representing 75 families. Of these, the larvae of the families Gonostomatidae or Phosichthyidae consistently occurred on both sides of the frontal zone, yet are exclusively of mesopelagic, deep‐oceanic origin; hence, they indicate Gulf Stream‐to‐shelf water‐exchange. The larvae of the clupeid, Brevoortia tyrannus, and the sciaenid, Leiostomus xanthurus, occurred on both sides of the frontal zone, yet spawn on the outer continental shelf in or near the Gulf Stream front; hence these taxa indicate shelf‐to‐Gulf Stream water‐exchange. The mechanisms of exchange, as indicated by the distribution of heat and salt across the front, along with satellite images of sea‐surface temperature, were not completely resolved, largely because of the two‐dimensional (x, z) rather than three‐dimensional (x, y, z) coordination employed. The observed distributions of indicator taxa did not always conform with expected, given the distribution of heat and salt across the front. Parcels of water exchanged across the front upstream (to the south) and encountered during observation along the cross‐shelf transects explains the lack of conformity. Where the expected and observed distributions agreed, the flux was 0.0009 larvae m−1 s−1 for the indicators of Gulf Stream‐to‐shelf exchange, and 0.0007–0.0030 larvae m−1 s−1 for the indicators of shelf‐to‐Gulf Stream exchange.

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.

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.

The Abundance of Fish Larvae in Estuaries: Within-Tide Variability at Inlet and Immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.

Applications of SABRE to research and management

In this paper, we highlight the major results from the SABRE programme and applications to research and management. In particular, SABRE provided new scientific insights into the fisheries oceanography of the estuarine‐dependent fishes of the South Atlantic Bight. Although we concentrated our efforts on Atlantic menhaden, we also gained insights on the coupling of physics to biology in the early life history of a number of marine fishes. Larval transport from spawning sites to and through barrier island inlets is now better understood. Analysis of menhaden population dynamics suggests survival in the late larval/early juvenile stage is particularly important to population growth. This phase of the life history appears likely to present a bottleneck to recruitment for Atlantic menhaden. We also made a number of technological breakthroughs which are already being applied elsewhere in research and assessments including the Continuous, Underway Egg Sampler (CUFES), enzyme‐based approaches to evaluating condition of individual larvae and various physical and biological modelling innovations. Our experiences establishing and managing the SABRE research team also provide insights into one model for promoting multidisciplinary research in fisheries oceanography. Throughout SABRE, we have sought an open exchange of information and insights from a wide variety of researchers and environmental managers. We hope the synthesis provided here continues that dialogue.

Spawning and transport dynamics of Atlantic menhaden: inferences from characteristics of immigrating larvae and predictions of a hydrodynamic model

We examined patterns of abundance, age and spawning date distributions of Atlantic menhaden Brevoortia tyrannus larvae immigrating during two seasons through three North Carolina inlets—Oregon, Ocracoke and Beaufort—to elucidate their spawning and transport dynamics. These patterns were examined in conjunction with corresponding predictions from a three‐dimensional, wind‐and tide‐driven hydrodynamic model. Larvae immigrating through different inlets showed consistent similarities as well as marked differences in temporal patterns of abundance, spawning dates and transport times. Intraseasonal patterns in abundance and spawning date distributions among inlets suggest that, in both study years, the spatio‐temporal dynamics of menhaden immigration were driven by large‐scale patterns along the Atlantic coast, rather than by localized variation in spawning activity. Interannual differences in the temporal patterns of spawning dates and larval immigration indicate interannual differences in transport dynamics and/or the spatial‐temporal distribution of spawning. When the spawning locations predicted by the hydrodynamic model are interpreted in conjunction with advanced very high resolution radiometer sea‐surface temperature information, the results are consistent with the limited historical information available on spatio‐temporal distribution of Atlantic menhaden eggs and larvae. The transport model also predicted distributions of arrival times for immigrating larvae that were comparable in range and variability with observed patterns. Our use of data from immigrating larvae, coupled with a hydrodynamic transport model and sea‐surface temperatures, allowed us to uncover relationships between spatio‐temporal patterns of Atlantic menhaden spawning and transport dynamics that could not have been identified by either approach alone.

Aphanomycesas a Cause of Ulcerative Skin Lesions of Menhaden from Chesapeake Bay Tributaries

During the summer and fall of 1997, an unusually high prevalence of skin lesions in fishes from Chesapeake Bay tributaries as well as two fish kills in the Pocomoke River stimulated significant public concern. Atlantic menhaden Brevoortia tyrannus were the most frequent target of the acute fish kills and displayed skin lesions that were attributed to the presence of the toxic dinoflagellate Pfiesteria piscicida. Hence, the penetrating skin ulcers so commonly found in this species are now widely viewed by the general public and some scientists as Pfiesteria-related and to be caused by exposure to Pfiesteria toxin. We examined, histologically, 121 menhaden with these ulcers collected from both Maryland and Virginia waters of the Chesapeake Bay in 1997 and 31 from the Pocomoke and Wicomico rivers in 1998. All of the deeply penetrating ulcers, as well as raised lesions (with or without eroded epithelium), were characterized by deeply penetrating fungal hyphae surrounded by chronic, granulomatous inflammation. These lesions had an appearance identical or similar to epizootic ulcerative syndrome (EUS), an ulcerative mycotic syndrome of fishes in other parts of the world caused by the fungal pathogen Aphanomyces invadans. They were also identical to ulcerative mycosis of menhaden previously reported along the Atlantic coast of the USA as associated with Aphanomyces spp. In 1998, using methods for isolation of A. invadans, we were able to culture from affected menhaden an Aphanomyces sp. that by preliminary tests is similar or identical to A. invadans. We believe these findings suggest that factors other than Pfiesteria toxin need to be considered as the cause or initiator of these lesions.

Purification and Characterization of Proteinase from Atlantic Menhaden Muscle

ABSTRACT:Two proteinases (A and B) were isolated from Atlantic menhaden muscle with molecular weights of 112,000 and 90,500 daltons, respectively. Proteinase B had higher activity than A for protein substrates except casein; proteinase B had no caseinolytic activity. Both proteinases hydrolyzed synthetic substrates such as Z‐Phe‐Arg‐NMecand TAME, but not BAEE and BAPNA. Optimum Z‐Phe‐Arg‐NMec hydrolyzing activity was shown at pH 7.4, 40 to 50 °C for both proteinases A and B. Activities of A and B in the presence of 3.0% NaCl were reduced to 71.2% and 62.2%, respectively. Both proteinases were inhibited by 1 mM TLCK, 1 mM benzamidine, 1% egg white, and 1% bovine plasma hydrolysate. Proteinases A and B are most likely tryptic serine type proteinases.

Purification and Characterization of Alkaline Proteinase from Atlantic Menhaden Muscle

ABSTRACT:Two alkaline proteinases (A and B) were isolated and found to be composed of homogeneous subunits. These proteinases, A and B, were concentrated 62.9‐and 986.5‐fold compared to the crude muscle extract, with molecular weights of 707,000 and 450,000, respectively. Both are probably serine type proteinases, and optimum caseinolytic activity was shown at pH 8.0 and 55 °C. Both degraded actomyosin under similar conditions. Enzyme A had higher thermal stability than B. The residual activities of A and B in 3.6% NaCl solution were 95% and 85%. These data suggest that these proteinases are involved in the softening of menhaden surimi gels which occurs during heating at 50 to 70 °C.