Retina-specific LDH isozyme in blueback herring, Alosa aestivalis (Mitchell), and alewife, Aiosa pseudoharengus (Wilson)

The retina of 390 Alosa aestivalis and 410 Alosa pseudoharengus have been examined by means of starch-gel electrophoresis. The retina-specific E₄ isozyme has been found to occur in all the fish examined. This study demonstrates for the first time that the E₄ isozyme occurs in A. aestivalis. Because the E₄ isozyme is not polymorphic and has an identical mobility in A. pseudoharengus and in A. aestivalis it is neither suitable for use as a species identification characteristic nor a population marker. Alosa aestivalis and Alosa pseudoharengus are two commercially important ana-dromous species of fish in New Brunswick, Canada. These two species may occur together in the same spawning runs but w^rhile A. pseudoharengus has a wide distribution along the East coast of North America (Leim & Scott, 1966) A. aestivalis occurs in a very limited area in Canada where it is at the northern limit of its range and because of increasing threat of pollution has been listed by McAllister (1970) as one of 17 endangered species. These two species of fish are morphologically very similar and can only be separated by the colour of the abdominal peritoneum (Leim & Scott, 1966). McKenzie (1973) has compared these two species by means of protein electrophoresis and found that while the muscle myogen patterns were species specific, the LDH patterns were the same in both species. He described these two species as five isozyme fish showing the LDH isozymes A₄, A₃B, A₂B₂, AB₃ and B₄. Since Horowitz & Whitt (1972) have reported the presence of the E₄ isozyme in the retina of some teleosts including. A. pseudoharengus but not including A. aestivalis, I considered it worth-while to re-examine A. aestivalis and A. pseudoharengus to find out whether A. aestivalis possessed this isozyme and, if so, whether the mobility of the isozyme could be used as a species identification characteristic and as a population marker. The fish used in this study were collected from five different locations during the 1971 spring migration period and held deep frozen for eight months before they were examined. They were identical to the specimens used for the study reported by McKenzie (1973) where the collection dates, numbers of fish and geographic locations are given. One eyeball from each of 390 A. aestivalis and 410 A. pseudoharengus was removed. Each eyeball was homogenized in 10 drops of distilled water and allowed to stand for one hour at 4^oC. The samples were then centrifuged for 10 min at 12 000 g. The supernatants were used immediately for vertical starch-gel electrophoresis. The apparatus used was that described by Boyer & Hiner (1963). The conditions of electrophoresis were the same as used by Saunders & McKenzie (1971). The LDH bands were stained by the deposition of blue formazan dyes in the regions of LDH activity. The stain formula and details of methods are given in Whitt (1970). The LDH isozyme patterns of all the fish examined were identical. The location of the isozymes A₄, A₃B, A₂B₂, AB₃ and B₄ are indicated in Fig. 1. A₄ is abundant in muscle while B₄ is abundant in heart. Because the LDH subunits assemble preferentially into homodimeric pairs before forming tetramers (Markert & Ursprung, 1971). A₄. A₂B₂ and B₄ show up in electropherograms as strong bands while A₃B and AB₃ show up as weak bands. The retina-specific isozyme E₄ is shown between B₄ and AB₃. Whitt (1970) has already demonstrated that A. pseudoharengus is a five isozyme fish. This has been confirmed by McKenzie (1973) who also compared both A. pseudoharengus and A. aestivalis and found these five isozymes had identical mobilities in both species of fish. The present study demonstrates for the first time that the retina-specific E₄ occurs in A. aestivalis where it has the same electro-phoretic mobility as that of A. pseudoharengus. The patterns are the same and do not appear to vary with geographic origin of the fish. The reason why the presence of the E₄ isozyme was demonstrated in the present study and not in the previous one (McKenzie, 1973) is because of the method used. In that study the migration length was not long enough to sufficiently separate the enzymes. In the present study vertical starch-gel electrophoresis which allows for long migration distances was used. As has already been shown for the A-B isozymes (McKenzie, 1973), the E₄ isozyme is not polymorphic in these two species of fish. It therefore has no use as apopulation marker. Because the E₄ isozyme has an identical mobility in both species of fish, it cannot be used as a species identification characteristic.     

Diel variation in density, length composition, and feeding activity of juvenile alewife, Alosa pseudoharengus Wilson, and blueback herring, A. aestivalis Mitchill, at near-surface depths in a hydroelectric dam impoundment

Catches ofjuvenile blueback herring in near-surface (0 to 1.5 m depth) waters, although greater at night than during the day, did not exhibit a strict negative phototropism because catches increased significantly with increasing illumination level during the forenoon and decreased with decreasing illumination during the afternoon. Juvenile alewife were absent from near-surface waters during daylight. Feeding activity by blueback herring increased between dawn and dusk and ceased or slowed overnight but was not strictly positively phototropic. Low power (1-β) of statistical tests due to high sampling variability and low (in hindsight) sample sizes precluded conclusions about the absence of die1 and spatial differences in the pattern of density, length composition, and of feeding activity of juvenile Alosa in those cases where the null hypothesis could not be rejected. Acceptable statistical power would require substantially increased (perhaps impractically so) sample sizes aided by an increase in a (probability of a type I error) from 0.05 to 0.1.     

Population structure and biology of alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) in the Saint John River,New Brunswick

Synopsis Examination of more than 2,000 alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) from various areas in the Saint John River, N.B., showed differences in their morphometric and meristic characters. They differed also in length and age, compositions, spawning time, length and age at maturity, back-calculated lengths, and growth parameters. Within each species, between-area comparisons showed significant differences in some of their meristic characteristics.To test a homing hypothesis for alewives, a multivariate analysis was performed on eight meristic characters. Two discriminant function programs, discriminant analysis for two groups and a multiple group stepwise discriminant analyses were used. Values of the generalized Mahalanobis D² and percent overlap in frequency distributions of meristic characters suggest that considerable straying of fish, especially between adjacent areas occurs during upstream spawning migration.This article is one of several papers presented at the Second European Ichthyological Congress, Paris, 8–15 September 1976, to be published in Environmental Biology of Fishes.     

Diet of alewives,Alosa pseudoharengus and blueback herring,A. aestivalis (Pisces: Clupeidae) in Minas Basin,Nova Scotia,a turbid,macrotidal estuary

Synopsis Stomach contents of anadromous alewives, Alosa pseudoharengus and blueback herring, A. aestivalis, obtained from brush weir and drift net collections in Minas Basin, N.S., were examined. Diets showed much overlap in terms of resource use, but the dietary importance of major prey categories differed substantially between species. Alewives favoured larger, more benthic prey (e.g. amphipods, mysids and crangonids), while blueback herring appeared to concentrate their feeding on microzooplankters (e.g. calanoid copepods, cypris larvae and molluscan veligers). Interspecific differences in diet composition are largely attributed to the planktivorous feeding habits of small (81–155 mm fork length) blueback herring. Differences in prey suggest that alewives utilize a particulate feeding strategy while blueback herring are predominantly filter-feeders. Although competition for food in the Basin seems unlikely since high secondary production yields a superabundance of prey, differences in feeding behaviour between younger, smaller individuals of both species could be a means of avoiding competitive interactions in an environment where there are space/access limitations imposed by the tidal cycle.     

Foraging behaviors and the interaction of alewife,Alosa pseudoharengus,and bloater,Coregonus hoyi

Synopsis Alewife, Alosa pseudoharengus, and bloater, Coregonus hoyi, are common planktivores in Lake Michigan. Both alewife and bloater use a variety of feeding modes. Alewives can filter, gulp and particulate feed; bloaters can only gulp and particulate feed. We examined handling time per prey and probability of capture for alewife and bloater particulate feeding on Mysis relicta. Using these estimates and available data for filtering alewives, cost curves were derived for alewife and bloater particulate feeding and for alewife using all three modes of feeding. Alewives filter small prey relative to their own body size and particulate feed on larger prey. Feeding mode appears to be dependent on prey size and density and shifts in feeding mode are apparently based on maximizing biomass eaten per time. The ability to filter confers a competitive advantage on alewife when small prey are abundant as they were in the mid 1960s in Lake Michigan. If the zooplankton are large, bloater young-of-year do not suffer this relative disadvantage. In fact, large bloaters can consume prey on the bottom not available to alewife. This shifting competitive balance may explain, in part, the observed dynamics of alewife and bloater.     

Genetic diversity and structure of two hybridizing anadromous fishes (Alosa pseudoharengus,Alosa aestivalis) across the northern portion of their ranges

Alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), also known collectively as either river herring or gaspereau, are anadromous clupeid fishes that display spatiotemporal overlap during riverine spawning migrations. Both species have experienced severe population declines within portions of their ranges. Evidence that they home to their natal rivers to spawn suggests the likelihood of ecologically significant population structure, yet this hypothesis has not been rigorously tested. We examined genetic diversity, differentiation and population structure in 34 alewife and four blueback herring populations spanning a 2,500 km portion of their northern range, using 14 microsatellite loci. Significant differentiation was detected among most rivers, and eight genetically defined alewife population clusters that largely corresponded to hydrographic regions were identified. Similar population structure was seen for blueback herring. Genetic isolation by distance was not significant among alewife populations in regions that have been historically influenced by dams, and/or stock transfers, but was highly significant in two regions that have not been subject to these influences. Genetic differentiation of alewife populations was strongest in the Bay of Fundy. Bottleneck tests revealed evidence of demographic bottlenecks in all of the alewife populations. Lastly, our results indicated that hybridization between alewife and blueback herring is common.     

The rostral pars distalis of the pituitary gland of the freshwater and marine alewife (Alosa pseudoharengus)

Summary In the alewife the orohypophyseal duct, a remnant of Rathke's pouch, persists in adults as a tube passing from the rostral pars distalis to the pharyngeal region. Its lumen is not open to the buccal cavity. The prolactin cells are situated around the bifurcations of this duct in the rostral pars distalis. Contents from prolactin cells, such as granules, nuclei, mitochondria and Golgi structures were found in these bifurcations. These contents were indistinguishable from those of intact prolactin cells. Evidence of actual release into the duct was often noted. At the presumptive point of release, the cells lining the lumen separate and the contents, probably of an entire prolactin cell, are extruded. The cilia usually found at the point of extrusion arise from prolactin cells. The prolactin cells of freshwater fish were more heavily granulated than those from a marine environment. Prolactin cells of fish entering freshwater streams were not heavily granulated but showed evidence of increased activity. Granule size was not affected by salinity. The ACTH cells are arranged in bands along branches of the neurohypophysis in the rostral pars distalis. No differences in ACTH cells from fish of different salinities were noted.We would like to thank Mr. D. D. Zumwalt of the John G. Shedd Aquarium in Chicago, Dr. E. D. Warner, Mr. R. L. Flayter, Dr. J. G. Stanley of the University of Wisconsin, Milwaukee, Mr. L. Wells of the U. S. Fish and Wildlife Service, Great Lakes Fisheries Laboratory, Ann Arbor, and Mr. L. N. Flagg of the Department of Sea and Shore Fisheries, Augusta, Maine, for their assistance in obtaining the fish used in this study. Dr. T. N. Tahmisian and Mr. G. T. Chubb of Argonne National Laboratories, and Dr. L. M. Srivastava and Dr. V. Bourne of Simon Fraser University, Canada, kindly made electron microscope facilities available. Finally, we wish to thank Mr. W. Goossens and Mr. D. J. DeJong for valuable assistance. This project was supported by a grant from the National Marine Fisheries Service.     

Life history variations in populations of American shad, Alosa sapidissima (Wilson), spawning in tributaries of the St John River, New Brunswick

Shad were sampled at four locations in the St John River area, New Brunswick; St John Harbour, Kennebecasis River, Washademoak Lake and Mactaquac Dam. The effect of the St John Harbour fishery on upstream spawning populations was minimal. Mactaquac Dam began operation in 1967 and since that time the populations of shad arriving at that facility have been in a state of flux. When shad populations from Kennebecasis River and Washademoak L. were compared, the Washademoak Lake population exhibited higher relative fecundity, lower mean age at maturity and possessed a lower proportion of repeat spawners. The combinations of reproductive characteristics occurring in the populations of the St John River were the same as those occurring over the Atlantic coast range of shad. The possible environmental factors influencing the variations in reproductive characteristics are discussed.     

Genetic variation of Azov and Black sea herring Alosa pontica (Eihwald, 1838), (Clupeiformes, Alosinae) in Danube river: analysis of biochemical gene markers

Genetic variation and structure of Danube stock of Aloca pontica pontica were investigated during the spawning moving by means of biochemical genetic marking. The level of heterozygosity was Hobs = 0,009. It is essentially lower than the average level for populations of other Teleostei and Clupeidae representatives. Polymorphism was defined only for Es-D of 20 analyzed loci expressed in muscle tissues. The allele frequencies for this locus were reliably different in the early spawning and later spawning parts of the stock, as well as proportion of heterozygotes and genotype diversity which was higher at the beginning of spawning moving. These results are discussed from two points of view: genetic differences between subpopulations in the course of spawning moving and presence of two close species of herring which come for the spawning together and hybridize to each other.     

An experimental investigation of a direct life-cycle in Reighardia sternae (Diesing, 1864), a pentastomid parasite of the herring gull (Larus argentatus).

A direct life-cycle in Reighardia sternae, a cephalobaenid pentastomid of gulls was investigated: the work was prompted by a report of eggs and larvae recovered from the stomach and intestine of a naturally infected gull. Infective pentastomid eggs were obtained by surgically transplanting maturing female Reighardia, taken from freshly shot wild gulls, into captive recipients. Faecal material from birds thus artificially infected was collected daily and examined for eggs. Eggs were force fed to 33 hand-reared (from eggs or nestlings) juvenile gulls which were selected at random and sacrificed at intervals thereafter and examined for pentastomids. One hour after infection, primary larvae appear in the body cavity where they moult immediately. They grow steadily and by 27-35 days are sexually differentiated, and by 66 days have copulated. Fertilized females take a further 116 days to produce eggs by which time they are 7-6 cm long. The complex migrations undertaken by developing larvae in the gull, and the problems of the mechanism of direct transmission, are discussed.     

Growth and movements of the twaite shad, Alosa fallax (Lacépède), in the Severn Estuary

Between July 1974 and April 1977, appreciable numbers of 0 group twaite shad, Alosa fallax , have been collected from the cooling water intake screens of the Nuclear Power Stations at Oldbury-upon-Severn and Berkeley on the Severn Estuary and at Hinkley Point on the Bristol Channel, England. Young of the year first appeared at Oldbury in July at a size of approximately 32 mm standard length, and grew to approximately 61 mm by October. The downstream migration in the late summer and autumn appeared to be closely correlated with water temperature since movement reached a peak soon after the temperature in the Estuary had declined below 19° C, and ceased altogether below 9° C. Thereafter, there was virtually no movement of shad until temperatures rose sharply above 7° C in the spring. Maturing adult twaite shad were captured in late April and May as they moved into freshwater to spawn, probably in mid-June. Males were recorded slightly earlier during the migration and were generally younger than females. Furthermore, mean lengths and weights for individuals belonging to the different age classes indicated that males were also smaller. Logarithmic relationships between length and weight of young and adult A. fallax and for the variation with size in the number of rakers on the first gill arch are presented.     

Spawning of the Australian freshwater fish Murray cod, Maccullochella peeli (Mitchell), in earthen ponds

Murray cod, Maccullochella peeli , spawned naturally in earthen ponds in four consecutive breeding seasons. Spawning was induced by a rise in water temperature up to or above 20°C during spring, however, an associated rise in water level was not required. Response to the temperature rise was more rapid later in the season and increasing daylength may have also been involved. Eggs were deposited on firm substrates at depths between 0·5 and 2·3 m, and hollow pipes, logs or similar structures were not necessary to provide suitable sites for egg deposition. At two spawning sites, mud had been removed from the pond banks by the broodfish and the eggs attached to the exposed clay. At one spawning site, a male cod was observed protecting the eggs during incubation.
It is suggested that high survival of cod larvae will only occur when a significant rise in water level coincides with the breeding season and as a consequence the control of water levels for irrigation and flood mitigation purposes during spring and summer has affected Murray cod to a greater extent than golden perch, Macauaria ambigua , which spawns only after a substantial rise in water level, when conditions are more favourable for larval survival.     

The biology of the twaite shad, Alosa fallax fallax (Lacépède), in the Severn Estuary

The estuarine biology of the twaite shad was studied in the Severn Estuary. Adults enter the estuary at the start of the freshwater phase of their spawning migration between April and June. Peak immigration generally occurs in May and is associated with temperatures in the range 10.6–12.3°C. The mean (± s.d. ) instantaneous mortality rate for the mature population was 0.53±0.18. The effect of additional mortality on the spawning population was modelled assuming constant recruitment and no density-dependent effects.
Juvenile twaite shad are present in the estuary from July until they emigrate seaward during the autumn. A portion of these fish re-enter the estuary the following April–May and remain until late summer/early autumn before once more migrating seaward.
The 0 + age group feed mainly on harpacticoid and calanoid copepods and mysids, the relative preponderance of these in the diet being apparently related to tidal conditions. The possible implications of the proposed tidal power barrage in the Severn Estuary on the twaite shad population are discussed in relation to movement, diet and additional mortality of the mature population.