Mitochondrial genome of the American shad Alosa sapidissima

The complete mitochondrial genome of Alosa sapidissima has been determined. The total length of the mitogenome was 16,697 bp and had a gene content (13 protein-coding, 22 tRNAs and 2 rRNAs. Except for the seven tRNA and Nd6 genes, all other mitochondrial genes are encoded on the heavy strand. The overall base composition of the heavy strand is 28.3% A, 24.8% T, 28.9% C, 17.9% G, with an AT content of 53.1%. The DNA sequence of Alosa. sapidissima shared 97.1, 93.9, 88.8 and 82.3% sequence identity with that of Alosa alosa, Alosa pseudoharengus. Molecular data here presented provide a useful toll for evolutionary as well as population genetic studied.     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

Circadian rhythms in juvenile american shad, Alosa sapidissima

Swimming activity (in cm s⁻¹) of a school (55 individuals) of young-of-the-year ( total length=110 mm) American shad, Alosa sapidissima , was determined under a variety of photoperiod conditions. These included a normal (ambient), a shifted, and constant-light day. Swimming activity was measured over 4-day periods. During normal days swimming speeds followed periods of about 24 h, with fast speeds (up to 45 cm s⁻¹) and schooling occurring during the photoperiod. Under dark conditions speeds were slower (8 cm s⁻¹) with most fish swimming as individuals. During a shifted day swimming speeds and schooling corresponded to the imposed day. Under constant light (equivalent to bright moonlight) no schooling was evident, and a constant, but slow, swimming speed was observed in each 24-h period. These shad demonstrated an exogenous rhythm with respect to the imposed day length. It is hypothesized that an endogenous circadian rhythm would only be of use to a fish required to hunt or chase its prey. Shad, being plankton feeders, do not chase prey and therefore can exhibit an exogenous circadian rhythm with no detrimental feeding results.     

Developmental and environmental regulation of chloride cells in young American shad, Alosa sapidissima

Location, abundance, and morphology of gill chloride cells were quantified during changes in osmoregulatory physiology accompanying early development in American shad, Alosa sapidissima. During the larval-juvenile transition of shad, gill chloride cells increased 3.5-fold in abundance coincident with gill formation, increased seawater tolerance, and increased Na(+),K(+)-ATPase activity. Chloride cells were found on both the primary filament and secondary lamellae in pre-migratory juveniles. Chloride cells on both the primary filament and secondary lamellae increased in abundance (1.5- to 2-fold) and size (2- to 2.5-fold) in juveniles held in fresh water from August 31 to December 1 (the period of downstream migration) under declining temperature. This proliferation of chloride cells was correlated with physiological changes associated with migration (decreased hyperosmoregulatory ability and increased gill Na(+),K(+)-ATPase activity). Increases in chloride cell size and number of fish in fresh water were delayed and of a lower magnitude when shad were maintained at constant temperature (24 degrees C). When juveniles were acclimated to seawater, chloride cell abundance on the primary filament did not (though size increased 1.5- to 2-fold), but cells on the secondary lamellae disappeared. Na(+),K(+)-ATPase was immunolocalized to chloride cells in both fresh water and seawater acclimated fish. The disappearance of chloride cells on the secondary lamellae upon seawater acclimation is evidence that their role is confined to fresh water. The proliferation of chloride cells in fresh water during the migratory-associated loss of hyperosmoregulatory ability is likely to be a compensatory mechanism for increasing ion uptake. J. Exp. Zool. 290:73-87, 2001.     

美国鲥鱼对我国淡水生态系统的潜在入侵风险

近年来美国鲥鱼已被引入到我国的上海和广东等地进行水产养殖。本实验报道了在纯淡水人工养殖条件下美国鲥鱼的繁殖和生长情况。人工养殖鲥鱼的生长速度接近美国北卡罗莱纳州沿岸野生鲥鱼的生长速度,而高于特拉华河野生鲥鱼的生长速度;人工养殖的2龄鲥鱼既可以在养殖池中自然产卵,也可以通过注射激素人工诱导产卵,其平均受精率、孵化率和仔鱼17天内的存活率分别约15%、75%和54%。这一结果表明,尽管鲥鱼是在海水中进行繁殖的洄游性鱼类,但在生长环境适宜的淡水条件下同样可以正常生长,并达到性成熟和繁育后代,有可能在适宜的淡水水体中形成自我维持的种群。结合本实验结果和美国鲥鱼的其他生物学特性,本文认为美国鲥鱼在我国天然水体生态系统中具有潜在的入侵性。     

The nematode Anisakis simplex in American shad (Alosa sapidissima) in two Oregon rivers

This paper represents the first report of the nematode Anisakis simplex in the American shad (Alosa sapidissima) in its introduced range in the American Pacific Northwest. All the adult shad sampled from spawning populations in the Willamette (n = 9) and Umpqua (n = 12) rivers were infected with A. simplex with intensities ranging from 6 to 89 worms per fish. This preliminary investigation contrasts sharply with previous studies in the native range of American shad and confirms that this fish may be an important intermediate host for A. simplex in the Pacific Northwest. It is suggested that this new parasite-host relationship has led to an ecological expansion into rivers and Anisakis may present an emerging health risk for wildlife and some human consumers.     

Feeding ecology of larval and juvenile American shad (Alosa sapidissima) in a small pond

Release ponds are used as part of a multifacet effort to restore American shad ( Alosa sapidissima ) in the upper Susquehanna River basin. Little information exists, however, on the feeding ecology of young shad in small ponds. Consequently, we examined feeding ecology and prey selection of 299 larval and 299 juvenile American shad in a small pond during spring and summer. Larval shad mainly consumed copepods (37.7%) and cladocerans (37.4%) whereas juvenile shad ate chironomids (43.1%) and ostracods (28.4%). Larval and juvenile shad exhibited diel variation in diet composition and feeding periodicity. Food consumption by shad was minimal at night; feeding activity was highest during the day, peaking at 2000 h for both larvae and juveniles. Electivity values of shad larvae for prey taxa were highest for cladocerans (+0.27) and lowest for ostracods (−0.07). Electivity values of juvenile shad were highest for chironomids (+ 0.21) and ostracods (+ 0.09), and lowest for copepods (− 0.08) and baetids (− 0.14). Our data indicate differences in diet composition, prey preference and, to a lesser extent, feeding patterns between larval and juvenile American shad in small pond environments.     

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 diversity and differentiation in a wide ranging anadromous fish,American shad (Alosa sapidissima), is correlated with latitude

Studies that span entire species ranges can provide insight into the relative roles of historical contingency and contemporary factors that influence population structure and can reveal patterns of genetic variation that might otherwise go undetected. American shad is a wide ranging anadromous clupeid fish that exhibits variation in demographic histories and reproductive strategies (both semelparity and iteroparity) and provides a unique perspective on the evolutionary processes that govern the genetic architecture of anadromous fishes. Using 13 microsatellite loci, we examined the magnitude and spatial distribution of genetic variation among 33 populations across the species' range to (i) determine whether signals of historical demography persist among contemporary populations and (ii) assess the effect of different reproductive strategies on population structure. Patterns of genetic diversity and differentiation among populations varied widely and reflect the differential influences of historical demography, microevolutionary processes and anthropogenic factors across the species' range. Sequential reductions of diversity with latitude among formerly glaciated rivers are consistent with stepwise postglacial colonization and successive population founder events. Weak differentiation among U.S. iteroparous populations may be a consequence of human‐mediated gene flow, while weak differentiation among semelparous populations probably reflects natural gene flow. Evidence for an effect of reproductive strategy on population structure suggests an important role for environmental variation and suggests that the factors that are responsible for shaping American shad life history patterns may also influence population genetic structure.     

Microsatellite DNA markers for American shad (Alosa sapidissima) and cross‐species amplification within the family Clupeidae

Sixteen microsatellite loci were identified and characterized for American shad (Alosa sapidissima). The number of alleles per locus observed ranged from eight to 32 and averaged 15.4 alleles. Average observed heterozygosity was 81.1%. The markers were screened using four other species from the family Clupeidae. Amplification success among Alosa species was 79.2% with 81.6% polymorphism among those markers that amplified successfully. Amplification success was poor in Dorosoma (31.3%). Due to allelic diversity and estimates of heterozygosity, these markers can be useful in A. sapidissima for population level analyses, parentage assignment and broodstock management.     

Proximate composition,lipid utilization and validation of a non‐lethal method to determine lipid content in migrating American shad Alosa sapidissima

Lipid content forms the most important energy reserve in anadromous fish and can limit survival, migration and reproductive success. A fat meter was evaluated and compared with a traditional extractive method of measuring available lipid for migrating American shad Alosa sapidissima in the Connecticut River, U.S.A. The fat meter gives rapid (<10 s) and non‐lethal lipid measurements, whereas traditional methods require lethal sampling that is both time consuming and expensive. The fat‐meter readings had a strong relationship to traditional lipid extractions for 60 fish, 30 whole body (R² = 0·72) and 30 fillet only (R² = 0·81). Additional validation showed that fat‐meter readings captured the gradual decrease of lipid in individual fish over time, were not affected by removal of gonads or scales and were stable for fish exposed to water or air for 24 h after death. These experiments indicate that the fat meter can be used as a reliable tool for future A. sapidissima energetic studies, allowing for larger sample sizes and non‐lethal sampling.     

Dissolved organic carbon fluxes in the Shetucket River of eastern Connecticut,U.S.A.*

SUMMARY. Seasonal changes in dissolved organic carbon (DOC) concentrations were monitored biweekly for 1 year at seven stations in the Shetucket River watershed in eastern Connecticut, U.S.A. Nine monthly diurnal studies revealed 24-h fluctuations of up to 53% of the seasonal range of 250–2200 μm DOC. Net DOC removal along a 1.9-km stretch below a secondary sewage treatment plant (activated sludge effluent diluted to a final average volume of 1.4% in the river) ranged from 0 to 1600 and averaged 68 ± 64 mmol m^?2 day^?1. Removal of DOC further downstream could only be observed during a severe 3-h October storm when net uptake ranged from 16 to 92 mmol m^?2 h^?1, using upstream-downstream techniques. Oxygen respiration could account for about half of the net DOC removal during the October storm. Even though net uptake was somewhat greater than reported in other lotic studies, about 97% of the DOC potentially available to benthic heterotrophs was exported further downstream.     

Climate change and the green energy paradox: the consequences for twaite shad Alosa fallax from the River Severn, U.K

A stock-recruitment model with a temperature component was used to estimate the effect of an increase in temperature predicted by climate change projections on population persistence and distribution of twaite shad Alosa fallax. An increase of 1 and 2° C above the current mean summer (June to August) water temperature of 17·8° C was estimated to result in a three and six-fold increase in the population, respectively. Climate change is also predicted to result in an earlier commencement to their spawning migration into fresh water. The model was expanded to investigate the effect of any additional mortality that might arise from a tidal power barrage across the Severn Estuary. Turbine mortality was separated into two components: (1) juvenile (pre-maturation) on their out migration during their first year and on their first return to the river to spawn and (2) post-maturation mortality on adults on the repeat spawning component of the population. Under current conditions, decreasing pre-maturation and post-maturation survival by 8% is estimated to result in the stock becoming extinct. It is estimated that an increase in mean summer water temperature of 1° C would mean that survival pre and post-maturation would need to be reduced by c. 10% before the stock becomes extinct. Therefore, climate change is likely to be beneficial to populations of A. fallax within U.K. rivers, increasing survival and thus, population persistence.     

Genetic polymorphism of adenosine deaminase (ADA; E.C. 3.5.4.4.) in allis shad, Alosa alosa and twaite shad, Alosa fallax

A genetic polymorphism of adenosine deaminase (ADA), is described for the first time in European shad species, Alosa alosa and Alosa fallax . Significant heterogeneity in gene frequencies was found, both between species and within species.     

A tumor growth inhibitory factor and a tumor growth promoting factor isolated from unfertilized ova of shad (Alosa sapidissima)

In the present study, a cytostatic tumor growth inhibitory peptide and a tumor growth promoting peptide with molecular weights of 20,000-30,000 Da have been identified in the supernatant fraction of unfertilized ova from Shad. The factors can be separated by gel chromatography, thus indicating that the factors are individual molecules. Both of the factors are nondialyzable, heat stable, and resistant to trypsin digestion and periodate oxidation.     

Organic matter processing by a stream-segment ecosystem: Fort River,Massachusetts, U.S.A.

An annual organic matter budget for a 1700 m segment of Fort River (Massachusetts, USA) is presented. Primary production in this fourth order stream exceeds litter input annually, however ecosystem P/R is 0.5. Respiration in excess of gross primary production is supported by allochthonous organic matter imported from upstream reaches. The relative contribution of organic matter size fractions to stream consumers depends upon biologic lability, rate of input, and residence time in the ecosystem. Particles of seston size (1 μm to 1 mm) are most heavily used by consumers, however dissolved organic matter represents the largest input component. Microorganisms are the predominant consumers in this soft-water, nutrient-poor stream ecosystem. A conceptual model for assessing the processing efficiency of stream ecosystems is presented and discussed in terms of several headwater to estuary gradients.     

Ovarian dynamics and fecundity regulation in blueback herring,Alosa aestivalis,from the Connecticut River,US

We analyzed ovarian dynamics of anadromous blueback herring, Alosa aestivalis, in Connecticut River with the principal aim of exploring oocyte recruitment and how it shapes the fecundity pattern. We examined the oocyte release strategy and analyzed spawning cyclicity by linking oocyte growth to the degeneration of postovulatory follicles. Females were accordingly classified as pre-spawners, early and late active spawners, and oocyte recruitment intensity was compared among the different spawning phases. Oocyte recruitment occurred continuously and in parallel with spawning activity, a pattern which is diagnostic of indeterminate fecundity. However, both fecundity and oocyte recruitment intensity progressively decreased (tapered) throughout spawning, until the ovary was depleted of vitellogenic oocytes. There was no massive atresia of vitellogenic oocytes at the end of the spawning season, which is atypical of indeterminate spawners. We propose that tapering in oocyte recruitment and fecundity is an adaptation to the high energetic expenditure of the upstream spawning migration.