Metazoan parasites of Engraulis ringens as tools for stock discrimination along the Chilean coast

The value of the metazoan parasites of the anchoveta Engraulis ringens as biological tags for stock discrimination is assessed. Three hundred and fifty-nine specimens, obtained from six landing ports in northern and central Chile (Arica, Antofagasta, Caldera, Coquimbo, Valparaiso and Talcahuano) covering a latitudinal gradient of c . 18°, were analysed. Six metazoan parasite species (three ectoparasites and three endoparasites) were obtained. A correspondence analysis suggested that anchoveta from northern and central Chile are comprised of two stocks. Identification of stocks was largely based on qualitative differences (absence in southern localities of the monogenean Pseudanthocotyloides heterocotyle , a parasite proper of engraulids, and the copepod Caligus sp.) and quantitative differences in the prevalence of infection for the remaining species. Inertia and mass value for the correspondence analysis supported the hypothesis of two stocks.     

Stock and parental effects on embryonic and early larval development of winter flounder Pseudopleuronectes americanus (Walbaum)

A hierarchical breeding design was used to determine if winter flounder Pseudopleuronectes americanus embryos and yolk-sac larvae sired by Georges Bank males developed and grew larger than fish sired by Passamaquoddy Bay males, and to examine parental contributions to variations in fertilization success, time to 50% hatch, hatch success and larval morphological development. Significant stock effects were detected for time to hatch and larval development. Eggs fertilized by Passamaquoddy Bay males reached 50% hatch significantly earlier than eggs fertilized by Georges Bank males. Larvae sired by Georges Bank males were significantly larger during larval development for four of the six traits measured at 12 days post-hatch: head depth, jaw length, myotome height and body area. Embryo and larval development were strongly influenced by maternal contributions; there were significant maternal variance components for the majority of the variables measured. Paternal variance components were significant for fertilization success, time to hatch, larval jaw length and larval head depth, however, they acted principally through parental interactions. This information has important implications for the long-term sustainable development of winter flounder for aquaculture purposes as well as for understanding winter flounder genetic variation in the wild.     

A map of barley chromosome 2 using isozymic and morphological markers

The F₂ progeny of a cross between a chromosome 2 multiple marker stock and an adapted cultivar of barley were analyzed for four morphological markers and electrophoretic patterns of eight leaf isozymes. TheIdh-2 locus was linked to thePer-5 locus (27.96±5.07 cM) and to thee locus (10.26±3.13 cM). Also, thePer-5 ande loci were located on the short arm of chromosome 2. In additionIdh-2 was also located on barley chromosome 2 and was linked to thev locus (13.18±3.56 cM), which is located on the long arm of chromosome 2. Two other marker genes,li andwst,,B, were linked (26.50±5.24 cM) on chromosome 2 but segregate independently of the other loci evaluated. This project was supported by funds from the U.S.-Spain Joint Committee for Scientific and Technological Cooperation.     

Small marine pelagic fish and the threat of fishing; are they endangered?

Evidence of the collapse and recovery of major marine fisheries for pelagic fish species is reviewed, distinguishing the influence of fishing compared with natural (environmental) effects. In one only of the best documented cases (Icelandic spring-spawning herring) has the stock failed to reappear, after 20 years. Several others, e.g. California sardine, have persisted at 1/000th or possibly less of their peak size for some years before beginning to recover. Fishing has been the main cause of collapse in most but not all cases, due initially to the escalation of catchability as stock size decreases–a phenomenon characteristic of fisheries for pelagic species due to their shoaling habit, ease of detection and vulnerability to modern fishing methods. It is concluded that although the threat of fishing to the continuity of the species is remote, excessive depletion (although avoidable by firm and timely management) is potentially able to cause temporary disappearance of local stock and disruption of the ecosystem.     

A meristic, morphometric and biochemical investigation of Atlantic menhaden, Brevoortia tyrannus (Latrobe)

Juvenile Atlantic menhaden, Brevoortia tyrannus , were collected from estuarine waters of the Atlantic coast of the United States. Those collected north of latitude 40°N had lower numbers of total and trunk vertebrae, ventral scutes and interhaemal spines, and shallower heads, smaller eyes, shorter predorsal lengths, and lower frequencies of the fastest allele observed at the transferrin locus than those collected south of Long Island. Although the evidence is still inconclusive, the potential for at least two subpopulations still exists: one which spawns in the spring and early summer and is responsible for the primary recruitment in the northern North Atlantic area, and one which spawns in the autumn and winter and contributes the majority of recruitment in the middle and southern North Atlantic areas of the United States.     

Germination, seedling morphology and establishment of Cotnbretum bauchiense Hutch. & Dalz. (Combretaceae)

ONYEKWELU, S. S. C, 1990. Germination, seedling morphology and establishment of Cotnbretum bauchiense Hutch. & Dalz. (Combretaceae). Cotnbretum bauchiense is a suffrutex with short, erect, usually herbaceous stems arising from a woody root stock. It appears in savanna soon after fire and (lowers within a few weeks. The fruits germinate in 5–6 days. The germination is cryptogeal. On germination the true radicle and the apparent radicle formed by fused cotyledon stalks push down into the soil, carrying the plumule with them. The cotyledon lamina and part of the fused cotyledon stalks remain above the soil. Both the apparent radicle and the true radicle produce roots. Below the soil at the joint of the apparent radicle and the true radicle the plumule produces 1–3 shoots which grow out to the surface of the soil. The underground portion of the shoot bears scale leaves, from which the plant regenerates when the aerial shoot is damaged by fire. This type of germination is an adaptation that ensures successful establishment in an environment that is subjected to fire.     

Application of a fry (0+;) abundance index, based on semi-quantitative electrofishing, to predict Atlantic salmon smolt runs in the River Bush, Northern Ireland

An abundance index for 0+ Atlantic salmon was based on semi-quantitative electrofishing estimates at 137 sites in typical juvenile habitat throughout the River Bush (N. Ireland). 0 + abundance was linearly related to total smolt numbers migrating through a downstream trap in subsequent years ( r ²= 0.716, P <0.001), suggesting a high degree of predictive ability. This predictive ability decreased as smolt age increased, suggesting influence of density-independent mortality. Potential application of the technique to estimate smolt production from rivers having no trapping facilities is discussed, together with sources of variability potentially affecting estimates.     

Mitochondrial DNA sequence variation and genetic stock structure of Atlantic cod (Gadus morhua) from bay and offshore locations on the Newfoundland continental shelf

Bay cod, Atlantic cod (Gadus morhua) that over-winter in the deep-water bays of northeastern Newfoundland, have historically been regarded as distinct in migration and spawning behaviour from offshore (Grand Bank) cod stocks. To investigate their genetic relationships, we determined the DNA sequence of a 307-base-pair portion of the mitochondrial cytochrome b gene for 236 adult cod taken from the waters off northeastern Newfoundland, including fish found over-wintering and spawning in Trinity Bay. Although 17 genotypes were found, a single common genotype occurs at a frequency of greater than 80% in all samples, and no alternative genotype occurs at a frequency of greater than 3%. Genotype proportions did not differ significantly among samples. Measures of genetic subdivision among sampling locations are nil. Cod over-wintering in Trinity Bay are not genetically distinct from offshore cod. In combination with tagging and physiological studies, these data suggest that there is sufficient movement of cod between bay and offshore locations to prevent the development or maintenance of independent inshore stocks. Adult cod that over-winter in Trinity Bay appear to represent an assemblage of temporarily nonmigratory fish that have become physiologically acclimated to cold-water inshore environments. The pattern of genetic variation in northern cod suggests a recent population structure characterized by extensive movement of contemporary individuals superimposed on an older structure characterized by a bottleneck in the population size of cod in the north-western Atlantic.     

Effect of Acetate on Esterase C Activity During the Growth Cycle of Paramecium*

SYNOPSIS Enhanced esterase C activity could be demonstrated by starch gel electrophoresis in various stocks of Paramecium spp. (P. primaurelia stocks 90 and 540, P. biaurelia stock 93, P. tetraurelia stock 29. P. pentaurelia stock 87, P. octaurelia stocks 31 and 300, and P. multimicronucleatum species 3, stock 8 MO) grown in Adaptation Medium. This esterase, however, was barely detectable when they were cultivated in Axenic Medium. Addition of trypticase to Adaptation Medium resulted in reduction of esterase C in the ciliates. This effect is ascribable to Na acetate present in trypticase. Since esterase C increased with the decrease in acetate concentration (as estimated by gas-liquid chromatography) during growth of Paramecium, acetate appears to be utilized by the cells. Sensitivity of esterase C to acetate occurs in all 6 species of Paramecium examined. Different stocks within a species may have different levels of sensitivity; in one case this is genetically determined. The results emphasize the importance of controlling and manipulating growth conditions for the assessment of inter- and intraspecies variations in the isozymes of Paramecium.     

A direct approach to the measurement of genetic variation in fish populations: applications of the polymerase chain reaction to studies of Atlantic cod, Gadus morhua L.

We used the polymerase chain reaction (PCR) and direct DNA sequencing to study genetic variation within and among populations of Atlantic cod, Gadus morhua , in the western North Atlantic. In a 307 bp region of the mitochondrial cytochrome b gene, 24 variable nucleotide positions define 24 genotypes, which differ by from one to six nucleotide substitutions. Greenland cod ( G. ogac ) differs from the most similar G. morhua genotype by an additional 12 nucleotide substitutions. Silent transitions dominate both intra- and interspecific comparisons, however four nucleotide substitutions within morhua result in amino acid replacements. Direct sequencing of DNA reveals substantially more of the genetic variation that exists within and between species than do previous indirect methods based on restriction fragment length polymorphisms, and thus has far greater potential to quantify such differences as may exist among fish stocks. Preliminary experiments also indicate that automation of DNA sequencing provides an efficient, rapid, and accurate means for detection of genetic variation in natural populations offish.