Esterase polymorphism in vitreous fluid of Pacific hake, Merluccius productus

Three regions of esterase activity designated I, II, and III were found on zymograms of vitreous fluids. Region I, the most anodal, exhibited two zones, one of which (the slower) was in all samples, occasionally accompanied by a second band which moved just ahead of it. Likewise, Region III, the most cathodal, exhibited two phenotypes, a common one-band and a rare two-band phenotype. Region II was occupied by one- and two-banded combinations of five different zones (a, b, c, d and e), which indicated that each band was the product of an allelic series of genes (EsII ^a, EsII ^b, etc.).
Only 11 of 15 expected phenotypes were encountered because of the rarity of alleles EsII ^a and EsII ^c. The most common allele, EsII ^b, had a frequency of 0.83 in Puget Sound hake and 0.60 in Pacific Ocean hake; this difference was highly significant. In the Pacific Ocean population agreement was good between observed and expected numbers, assuming Hardy-Weinberg equilibrium. In the Puget Sound samples deviations from expected frequencies did not appear in females or first-year fish, but deviations were significant in males 2 years and older; these deviations occurred as a marked deficiency of bd males combined with an excess of bb and dd males, particularly the latter. Inhibition tests indicated that these isozymes are B esterases. Estimations of molecular weight for the isozymes of Region II based on chromatographic and ultracentrifugation methods were 70,000 and 73,500, respectively.     

Genetic Population Structure of Pacific Hake, Merluccius productus, in the Pacific Northwest

This study presents the first protein electrophoretic study of population structure within the Georgia Basin Pacific hake Distinct Population Segment, as defined under the U.S. Endangered Species Act. Forty-one allozyme loci (29 polymorphic) were analyzed in samples from three Pacific hake spawning populations on the west coast of North America: (1) Port Susan, Puget Sound, Washington (three temporal samples); (2) south-central Strait of Georgia, British Columbia, Canada (two temporal samples); and (3) offshore of southern California (two temporal samples) (total n = 664). Mean heterozygosity over all loci was 12–13% for all populations. Within-population temporal samples were not significantly different from one another, but statistically significant differences were detected at 15 of the 29 polymorphic loci (p < 0.05) among the three populations. Differences at eight of these loci were highly significant (p < 0.001): ADA ^*, ALAT ^*, bGALA ^*, GPI-A ^*, sIDHP ^*, LDH-A ^*, MPI ^*, and PEP-B ^*. The two Georgia Basin populations were significantly different at six loci: bGALA ^*, sIDHP ^*, LDH-A ^*, MPI ^*, PGK ^*, and PGM-2 ^* (p < 0.05). Nei's genetic distance (D) was 0.0006 between Port Susan and Strait of Georgia pooled temporal samples, and 0.005 between these populations and offshore Pacific hake. F_ST was 0.02 and 0.0046 among all three populations and among the Georgia Basin populations, respectively. Both F_ST estimates were significantly greater than zero, and the results suggest a high degree of demographic isolation among all three populations.     

Recent increase in Nybelinia surmenicola prevalence and intensity in Pacific hake (Merluccius productus) off the United States west coast

A larval marine cestode was found in 82.0% of 834 Pacific hake (Merluccius productus) stomachs collected from 341 trawl stations along the United States west coast during the summers of 2008 and 2009. Morphology and DNA sequencing was used to identify the cestode as Nybelinia surmenicola. In an examination of 131 Pacific hake stomachs collected from the same region in 1999, N. surmenicola prevalence was 35.1%. The results from a general linear model suggested that their prevalence is influenced by year and latitude, Pacific hake size, and sex. Mean intensity of N. surmenicola in 2008-2009 was 20.22 (±1.13 SE) and was positively related to Pacific hake length and the latitude of collection. Year-1 Pacific hake (<27 cm length) had significantly lower prevalence and intensity of N. surmenicola compared to older and larger fish. Pacific hake collected south of Point Conception, California (32.5 to 35°N) had lower prevalence and intensity of N. surmenicola compared to those collected in northern latitudes (35.1 to 48.4°N). Higher N. surmenicola prevalence in Pacific hake in recent years suggests food-web fluctuations in the northern California current ecosystem caused by changes in ocean transport of zooplankton or pelagic fish distributions and warrants future monitoring as a metric for ecosystem change.     

Fluid mechanosensory stimulation of behaviour from a planktonic marine copepod, Euchaeta rimana Bradford

This research provides the first reported thresholds for thebehavioural response of an individual planktonic copepod. Usinga novel technique to create near-field fluid disturbances, wedirected microlitre volumes of water towards the antennularysetae. In response to an increasing strength of this purelymechanical signal, the animal varied its behaviour from a rapidflick to a capture response and finally an escape reaction.This work provides a basis for addressing the criteria copepodsuse to interpret biologically generated signals to elicit anappropriate behavioural response and offers insight into howthese signals are differentiated from the random fluid motionin their environment.     

Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

Some ecological aspects of the copepod parasites of the common hake, Merluccius hubbsi, from the Argentine-Uruguayan coasts

A total of 2164 common hake Merluccius hubbsi captured in the Argentine-Uruguayan Common Fishing Zone was examined for parasitic copepods. The fish were infested with Chondracanlhus palpifer and Neobrachietia insidiosa f. lageniformis, the former parasitizing the buccal cavity and the latter the branchial arches. C. palpifer showed an increase in both prevalence and intensity in relation to the host size; infestation with N. insidiosa f. lageniformis decreased with increasing length of hake. Attachment site preferences and variations in the parasite distribution patterns as related to the host biology were observed. Evidence of negative association between copepod species and seasonal changes in the parasite composition was also found.     

Fish protein hydrolysis by a psychrotrophic marine bacterium isolated from the gut of hake (Merluccius hubbsi)

The aims of this study were to identify a psychrotrophic bacterium, strain CR41, producing a cold adapted protease during growth at low temperatures and to evaluate the ability of the cells to hydrolyze hake fish protein. The strain was isolated from the intestinal tract of hake collected from the San Jorge Gulf (Patagonia, Argentina) and it was identified as Pseudoalteromonas. Growth and fish protein hydrolysis were determined using an aerated simple mineral medium plus 10% fish protein concentrate. Proteolytic activity was measured at 7 and 22 degrees C during culture in the concentrate. Protease production started in the exponential growth phase and reached a maximum during stationary phase. Protease activity at 7 degrees C was lower than at 22 degrees C. After 8 h of incubation, the percentage of hydrolyzed protein was 84% at 7 degrees C and 95% at 22 degrees C. Electrophoresis detection showed that degradation of muscle hake proteins was complete at both temperatures, and in gelatin zymograms extracellular activity showed two proteolytic bands with apparent molecular masses of approximately 31.6 and 62 kDa.     

Populations and assemblages of parasites in hake, Merluccius gayi, from the southeastern Pacific Ocean: stock implications

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hake Merluccius gayi landed at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes for Grillotia dollfusi, Hysterothylacium sp., Clestobothrium crassiceps and Aporocotyle wilhelmi . More use should be made of the information on whole parasite assemblages including, for example, patterns of co-occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co-occurring taxa in community assemblages would remain undetected.     

Gyrodinium undulans Hulburt, a marine dinoflagellate feeding on the bloom-forming diatomOdontella aurita, and on copepod and rotifer eggs

The marine dinoflagellateGyrodinium undulans was discovered as a feeder on the planktonic diatomOdontella aurita. Every year, during winter and early spring, a certain percentage of cells of this bloom-forming diatom, in the Wadden Sea along the North Sea coast, was regularly found affected by the flagellate. Supplied with the food diatomO. aurita the dinoflagellate could be maintained successfully in clonal culture. The vegetative life cylce was studied, mainly by light microscopy on live material, with special regard to the mode of food uptake. Food is taken up by a so-called phagopod, emerging from the antapex of the flagellate. Only fluid or tiny prey material could be transported through the phagopod. Larger organelles like the chloroplasts ofOdontella are not ingested and are left behind in the diatom cell. Thereafter, the detached dinoflagellate reproduces by cell division, occasionally followed by a second division. As yet, stages of sexual reproduction and possible formation of resting cysts could not be recognized, neither from wild material nor from laboratory cultures. Palmelloid stages (sometimes with a delicate wall) occurring in ageing cultures may at least partly function as temporary resting stages. The winter speciesG. undulans strongly resemblesSyltodinium listii, a summer species feeding on copepod and rotifer eggs. Surprisingly, in a few cases this prey material was accepted byG. undulans as well, at least under culture conditions. When fed with copepod eggs, the dinoflagellate developed into a large trophont, giving rise thereafter by repeated binary fission to 4, 8 or 16 flagellates, as a result of a single feeding act. A re-examination of both species under simultaneous culture conditions is planned.     

Respiration rates of subitaneous eggs from a marine calanoid copepod: monitored by nanorespirometry

The oxygen consumption rate during embryogenesis of Acartia tonsa subitaneous eggs were measured at different temperatures (10, 15, 17, 21, 24 and 28°C) with nanorespirometry. The oxygen consumption was constant during the embryogenesis but increased rapidly at hatching time. The mean ± SD oxygen consumption rate increased exponentially with temperature and ranged from 0.09 ± 0.04 (10°C) to 0.54 ± 0.09 nmol O₂ egg⁻¹ h⁻¹ (28°C). The mean ± SD Q₁₀-value was 2.51 ± 0.15. Calculations of energy consumption during embryogenesis ranged from 1.86 to 18.28 mJ depending on temperature and development time. We conclude that the effect of temperature on oxygen consumption rate was far less important than the prolonged development time when calculating the energy consumed during embryogenesis.     

Distribution and abundance of European hake Merluccius merluccius (L.), eggs and larvae in the North East Atlantic waters in 1995 and 1998 in relation to hydrographic conditions

Plankton samples from surveys in 1995 and 1998 were analysedin order to study the spatial distribution of hake (Merlucciusmerluccius) eggs and larvae. The cruises covered an extensivearea from the south of the Bay of Biscay to the north-west ofIreland. This spatial distribution has been interpreted in relationto the direction and intensity of the dominant winds. An importantdecrease of eggs (69%) and larvae (27%) was observed from 1995to 1998. Hake showed continuous spawning from February to Julyin the area. The centroids of hake egg distribution indicateda northward displacement of the peak of spawning as the seasonprogresses. Spawning of hake was located close to the 200 mdepth isobath in the southern area (Bay of Biscay) and it spreadover the shelf in the area of the Celtic Sea. Eggs were mostabundant at 20 m depth temperatures between 12 and 12.5°C.The centroids of hake larvae distribution also showed a northwarddisplacement although not as strong as that of hake eggs. Thespatial distribution of hake larvae by size ranges showed importantdifferences between years: in 1995 it suggested inshore transportof larvae, from the spawning areas (close to the 200 m depthisobath) to nursery areas (closer to the coast) while in 1998it suggested offshore transport. This transport does not correspondwith the general wind regimes during those years. Thereforeit is concluded that the transport of the hake larvae to nurseryareas must be controlled by different hydrographic mechanismssuch as geostrophic currents in the Bay of Biscay and tidalcurrents in the northern areas.     

Predation, production and the organization of an estuarine copepod community

The copepod community of the estuaries near Beaufort, NC underwenta consistent seasonal succession from a spring assemblage dominatedby the medium-sized copepod Acartia tonsa (1 mm) to a summer—fallassemblage dominated by the small-bodied copepods Parvocalanuscrizsrirostris and Oithona colcarva (both 0.5 mm). However,in enclosure experiments during this period, A. tonsa dominatedthe community, due to higher growth rates and its predationon the nauplii of other species. Nutrient additions enhancedthe dominance by A. tonsa. The decline in abundance of A. tonsain the estuary was associated with increased abundance of planktivorousanchovies and silversides. In other enclosure experiments, planktivorousfish eliminated A. tonsa and other large copepods, althoughthey persisted in enclosures lacking fish. I conclude that predationby size-selective planktivorous fish prevents dominance by A.tonsa during summer—fall. ¹Present address: Institute of Marine Sciences, University ofNorth Carolina, 3407 Arendell Street, Morehead City, NC 28557,USA     

Predation byOligotricha striata caddis larvae on amphibian eggs: Effects of a high quality food on growth rate

In the field and also in the laboratoryOligotricha striata trichopteran larvae were observed to feed onRana temporaria eggs. Laboratory experiments revealed thatO. striata larvae preferred amphibian eggs to plant matter. The jelly-like sheath of the eggs was easily penetrated. A larva consumed 1 to 2 eggs per day. The supply of high quality food in the form of amphibian eggs was found to accelerate the growth ofO. striata larvae.     

Predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the cyclopoid copepod Cyclops vicinus: a laboratory investigation with mixed and single prey

We tested the outcome of predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the similar sized cyclopoid copepod Cyclops vicinus in laboratory experiments with mixed and single-prey. When ovigerous females and adult non-ovigerous females of the calanoid copepod and the cyclopoid copepod were offered in equal numbers to the fish in the mixed-prey experiments, the cyclopoid copepods were significantly more heavily preyed upon than the calanoids. Between 14 and 16 females of the cyclopoid copepod and only between 2 and 4 calanoids had been consumed after the observation period of two hours. The single-prey experiments revealed that the conspicuousness of the calanoid vs the cyclopoid depended on sex and gravidity. Ovigerous females of the cyclopoid copepod were slightly earlier detected by the fish than ovigerous females of the calanoid, probably a result of the highly visible egg-sacs carried by the cyclopoid females. Females without eggs and males of the cyclopoid copepod were recognized later by the predator than females without eggs or males of the calanoid, probably a result of the different behaviours of the different copepod taxa. Cyclopoids frequently congregated near the aquarium bottom while calanoids were closer to the water surface where they were better visible. The calanoid copepod could better escape the fish's attacks than the cyclopoid copepod. Egg-bearing females of both the calanoid and the cyclopoid copepod could significantly better escape than non-ovigerous females or males. Probably ovigerous females react very early to water disturbances caused by the predator. Activity measurements showed that the cyclopoid copepod displayed 2 to 4 times more hops per time unit than the calanoid. Probably the high number of jerky movements displayed by the cyclopoid attracted attention of the predator and contributed to its greater vulnerability.     

Predation on eggs and larvae ofHeliothis virescens [Lep.: Noctuidae] by an adult predator complex in cage studies on cotton

Predation by a predator complex consisting of adults of the lygaeidGeocoris punctipes (Say), the nabidsNabis roseipennis Reuter and/orTropiconabis capsiformis Germar and the coccinelids,Hippodamia convergens Guerin-Meneville andColeomegilla maculata (DeGeer) onHeliothis virescens (F.) eggs, 1st-instar larvae or both on late pinhead square and early bloom stage cotton was evaluated in field cages in Mississippi. Prey densities of 4 (11, 512/ha) or 8 per cage and predator: prey (P:p) ratios of 1∶1, 2∶1, 3∶1, 4∶1 and 5∶1 were used. Prey were labeled with phosphorus-32 or carbon-14 to determine predator ingestion and effectiveness. Average percent egg predation as a function of P:p ratio ranged from 2.1 to 12.1 for a 48 h period. The average percent predation on larvae as a function of P:p ratio ranged from 5.3 to 22.0. The hemiptera fed more than the coleoptera on larvae, andG. punctipes was the best egg predator. For the range of predator densities used, the average area of discovery for the predator complex was 6.98 × 10⁻³ m/day and 2.34 × 10⁻² m/day when exposed to eggs and larvae, respectively. Publication N^o 5936-Mississippi Agricultural and Forestry Experiment Station, Mississippi State, MS 39762.     

Diet of two large sympatric teleosts, the ling (Genypterus blacodes) and hake (Merluccius australis)

Ling and hake are tertiary consumers, and as a result both may have an important structuring role in marine communities. The diets of 2064 ling and 913 hake from Chatham Rise, New Zealand, were determined from examination of stomach contents. Ling was a benthic generalist, and hake a demersal piscivore. The diet of ling was characterised by benthic crustaceans, mainly Munida gracilis and Metanephrops challengeri, and demersal fishes, mainly Macrourids and scavenged offal from fishing vessels. The diet of hake was characterised by teleost fishes, mainly macrourids and merlucciids. Multivariate analyses using distance-based linear models found the most important predictors of diet variability were depth, fish length, and vessel type (whether the sample was collected from a commercial or research vessel) for ling, and fish length and vessel type for hake. There was no interspecific predation between ling and hake, and resource competition was largely restricted to macrourid prey, although the dominant macrourid species predated by ling and hake were different. Cluster analysis of average diet of intraspecific groups of ling and hake confirmed the persistent diet separation. Although size is a central factor in determining ecological processes, similar sized ling and hake had distinctly different foraging ecology, and therefore could influence the ecosystem in different ways, and be unequally affected by ecosystem fluctuations.     

Predation, behavior, and attachment by Chrysoperla plorabunda larvae on Brassica oleracea with different surface waxblooms

Predation by Chrysoperla plorabunda (Fitch) (Chrysopidae) first instars on Plutella xylostella (L.) (Plutellidae) neonates was measured on nine Brassica oleracea L. types with different surface wax crystal morphology. Forty-eight-hour survival of P. xylostella caged on leaves was significantly reduced by C. plorabunda on plants expressing glossy mutations that reduce surface waxbloom, but not on plants with normal waxbloom. During 5-min observations, C. plorabunda spent more time walking and less time scrambling (moving the legs with no locomotion) on glossy types than on the normal-wax types. Adhesive force produced by C. plorabunda on plant surfaces was 20 to 200-fold greater on glossy types than on normal-wax types. All the glossy types provided an advantage to C. plorabunda over normal-wax types by increasing the force of attachment to the leaf suface by the larvae, which in turn increased time allocated to walking, leading to greater predation of P. xylostella larvae. Among glossy and normal wax types together, attachment force and time allocated to walking were significantly correlated with predation by C. plorabunda. Within glossy or normal-wax types, however, these correlations were not significant. Neither time allocated to walking, nor attachment to the leaf surface was a predictor of predation by C. plorabunda within glossy or normal-wax types. Although diverse mechanisms therefore contribute to differences in predation, the results show that reduction in waxbloom can substantially affect the mobility and effectiveness of this generalist predator.     

The metabolism of wax ters and other lipids by the marine copepod, Calanus helgolandicus

The polyunsaturated wax esters which occur in an oil droplet in Calanus helgolandicus apparently serve as a short term reserve metabolic fuel. The lipids of the copepods were labeled by feeding them (14)C-labeled diatoms, Skeletonema costatum, after which starvation and turnover experiments were carried out. During starvation both wax esters and triglycerides are largely depleted within 72 hr, whereas cholesterol and phospholipid decreased at much slower rates.