Simulation of physically mediated variability in prey resources of a larval fish: a three-dimensional NPZ model

A three-dimensional biophysical nutrient–phytoplankton–zooplankton model was used to investigate the spatial and temporal dynamics of food resources for young walleye pollock in the western Gulf of Alaska, to further understanding of recruitment processes for pollock. We modeled nitrogen, phytoplankton, a large herbivorous grazer parameterized as Neocalanus spp. (the biomass dominant copepod in the Gulf), and the 13 stages (egg, naupliar and copepodite) of Pseudocalanus spp. (a major constituent of the diet of pollock) so that the appropriate size class of food for each size of larval pollock was represented. Model results identified an area between the Semidi and Shumagin Islands that may not be suitable as a nursery area early in the year due to low prey abundance. Modeled mesoscale eddies, previously hypothesized to be important for larval pollock retention in Shelikof Strait, contained higher prey concentrations than the surrounding waters when they were cyclonic. This work also help to understand the consistency of pollock spawning in time and space in Shelikof Strait, by examining the timing and location of prey availability which, along with transport, narrows the window for optimal spawning.     

Thermal stability of the synthetic peptides with the sequence of fish fast skeletal muscle tropomyosin

Tropomyosins from fish skeletal muscle show high amino acid sequence homology, although their thermal stability is clearly different among species. In order to determine the regions that are responsible for the stability of this protein, five synthetic peptides of 30mer were synthesized by Fmoc method, based on the sequence of walleye pollack Theragra chalcogramma fast skeletal muscle tropomyosin, namely, N terminal Met¹-Lys³⁰, the variable region Asp⁸⁴-Leu¹¹³, the middle region Val¹²⁸-Ala¹⁵⁷, the region containing the conservative Cys (Leu¹⁷⁶-Lys²⁰⁵), and C terminal Asp²⁵⁵-Ile²⁸⁴. The thermal stability of these peptides was measured by circular dichroism and differential scanning calorimetry. The helical contents of these peptides were decreased in a temperature-dependent manner, although they showed no clear melting temperature, suggesting that the enthalpy necessary for the complete denaturation of these peptides was low. Peptides Asp²⁵⁵-Ile²⁸⁴ and Asp⁸⁴-Leu¹¹³ showed the highest and second highest α-helical contents, respectively, and the other peptides gave rise to lower α-helical contents.     

Role of organic fertilizers in walleye (Sander vitreus) production in plastic‐lined culture ponds

This study used six 0.04 ha plastic‐lined ponds to compare the effects of a fertilization regime using a one‐time initial application of an organic fertilizer (alfalfa pellets) with the current regime of weekly applications of organic fertilizers on the abundance and distribution of aquatic invertebrates and walleye, Sander vitreus, fingerling production. Walleye, 3–4 days post hatch, were stocked on 1 May 2002 and harvested on 6–7 June 2002. Throughout the growing season, a ratio of 7:1 total nitrate‐nitrogen to total phosphorus was maintained in all ponds regardless of the treatment. Once fry were stocked, ponds in Treatment #1 were fertilized weekly with organic fertilizer (alfalfa pellets; 112 kg ha^?1 week^?1) for a total of 795 kg ha^?1 pond^?1. Ponds in Treatment #2 only received an initial application of alfalfa pellets (112 kg ha^?1). Ponds in Treatment #1 had significantly higher ammonia and nitrate levels as well as higher chironomid larvae but not zooplankton compared with the other treatment. At harvest, walleye in the Treatment #1 ponds were significantly longer and heavier; however, the survival and relative weight were not significantly different. These results suggest that weekly applications of organics are important for the benthic food base and growth of fingerling walleye reared in plastic‐lined ponds.     

Purification and Structural Aspects of Type I Collagen from Walleye Pollock (Theragra chalcogramma) Skin

Type I collagen was extracted from walleye pollock (Theragra chalcogramma) skin and purified by DEAE-52 cellulose chromatography and gel filtration chromatography with Sephacryl S-300 HR. Fourier transform infrared spectroscopy spectra and X-ray diffraction pattern showed the existence of a helical arrangement, with the distance between the molecular chains of 1.18 nm and the unit height, typical of the triple helix, of 0.27 nm. Scanning electron microscopy (SEM) revealed the collagen had a filamentary structure. Peptide mapping, obtained by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), indicated that peptides with the molecular weight of 1,470, 1,565, 1,570, 2,150, and 2,470 Da were the major products of trypsin digestion of pollock skin collagen.     

Sympatric walleye Sander vitreus and sauger Sander canadensis in large reservoirs: Variable isotopic niche size and overlap across multiple time scales

Walleye Sander vitreus (Mitchill) and sauger Sander canadensis (Griffith & Smith) may occupy similar niches in sympatric populations, but their long‐term resource use is poorly studied. Multi‐tissue (liver, muscle and bone) isotopic niche analyses were used to compare resource use by these species in two large reservoirs in Saskatchewan, Canada. Population isotopic niches were larger for sauger (1.73‰²–3.60‰²) than walleye (0.51‰²–2.61‰²) in Lake Diefenbaker, but opposite in Tobin Lake (sauger = 0.54‰²–2.57‰²; walleye = 1.30‰²–2.94‰²). Analyses of population overlap suggest that these species co‐exist via niche partitioning, but partitioning was more pronounced in Lake Diefenbaker (overlap = 6%–38%; Tobin Lake overlap = 18%–62%). The size of individual niches and levels of intra‐ and interspecific overlap among individual fish also varied with reservoir. This study shows that walleye and sauger use different resources across different time scales, but the degree of partitioning can vary markedly with environment.     

Geographical variations in infection by larval Anisakis simplex and Contracaecum osculatum (Nematoda, Anisakidae) in walleye pollock Theragra chalcogramma stocks off Hokkaido, Japan

ABSTRACT: Stocks of walleye pollock Theragra chalcogramma collected from: (i) the Sea of Japan (off Rebun Island and Kumaishi); (ii) the Pacific coast (off Shikabe and eastern Hokkaido); and (iii) Nemuro Strait off Hokkaido, northern Japan, were examined for anisakid nematodes during December 1999 to February 2000, and the prevalence and abundance of Anisakis simplex and Contracaecum osculatum larvae were compared among the various sampling sites for fish of the same size and age. Anisakis simplex was generally more abundant than C. osculatum . Infection by A. simplex varied between the aforementioned stocks of walleye pollock as well as within stocks, whereby fish from off Rebun Island and Nemuro Strait were infected the most, followed by those from off the Pacific coast and Kumaishi. Infection by C. osculatum differed between the host stocks, and C. osculatum was the most abundant among the fish from Nemuro Strait. The infection variations seemed to be due to differences in host growth rate, host feeding habit, and the distribution of marine mammal final hosts. The results indicate that these two larval nematodes are useful biological indicators for the population study of walleye pollock in Japanese waters.     

Interannual variability in hatching period and early growth of juvenile walleye pollock, Theragra chalcogramma, in the Pacific coastal area of Hokkaido

Juvenile walleye pollock of the Japanese Pacific population were collected from the Funka Bay [spawning ground; 16–64 mm fork length (FL)] in spring and the Doto area (nursery ground; 70–146 mm FL) in summer. Hatch dates were estimated by subtracting the number of otolith daily increments from sampling dates, and their early growth was back‐calculated using otolith radius–somatic length relationships. Interannual change of the hatching period was observed during 2000–02, and the peaks ranged from mid‐February in 2000 to early‐April in 2002. In 2000, when a strong year class occurred, early life history of the surviving juveniles could be characterized by early hatching and slower growth in the larval stage (<22 mm length). Higher growth rate in 2001 and 2002 did not always lead to good survival and recruitment success. Even though their growth was slow in 2000, the larvae hatched early in the season had larger body size on a given date than faster‐growing larvae hatched in later season in 2001 and 2002. Bigger individuals at a certain moment may have advantage for survival. The delay of hatching period may result in higher size‐selective mortality, and as a necessary consequence, back‐calculated growth in 2001 and 2002 could shift towards higher growth rate, although abundance of such a year class would be at the lower level. Variability in spawning period, early growth and their interaction might have a strong relation to larval survival through cumulative predation pressure or ontogenetic changes in food availability.     

Preventive effects of amino acids and glutathione on the formaldehyde-induced denaturation of myofibrillar proteins

ABSTRACT:     Formaldehyde (FA)-induced denaturation of myofibrillar proteins and its prevention were investigated by means of measuring the solubility, adenosine triphosphatase (ATPase) activity, and thermal gel formability of myofibrils and surimi proteins in the presence and absence of free amino acids and glutathione, reduced form. The addition of FA decreased the solubility of myofibrils in 0.5 M NaCl at pH 7.0 and 0°C depending on its concentration and incubation time. The solubility decrease was completely inhibited by the presence of equal, twofold, and threefold amounts of cysteine (Cys), glutathione, and histidine (His) to the amount of FA, respectively. Myofibrillar Ca-ATPase was markedly activated at the initial phase and then decreased later by the addition of FA. The K-ATPase was inactivated with an increase in the amount of FA. The FA-induced changes in both ATPase activities were inhibited in the presence of Cys and His. Thermal gel formability of surimi paste increased only in a short period after the addition of a low concentration of FA. Practically, FA inhibited the thermal gelation and setting effect through the inactivation of transglutaminase. In the presence of Cys, His or glutathione, a strong elastic surimi gel was produced because FA-induced detrimental effects were inhibited.     

Consumption estimates of walleye stocked as fry to suppress fathead minnow populations in west-central Minnesota wetlands

Abstract –  Fisheries managers throughout the Prairie Pothole Region of Minnesota often use semi-permanent and permanent wetland basins to extensively culture walleye Sander vitreus fry. Waterfowl managers have expressed concern over this practice because of the potential influence that fish have on food resources used by waterfowl during development and migration. It is well known that native fathead minnows Pimephales promelas can have detrimental effects on macroinvertebrates, zooplankton, water clarity, epiphyton, and macrophytes in wetlands. Because walleye commonly become piscivorous as soon as mouth gape allows, walleye fry may suppress fathead minnow populations and improve wetland conditions for waterfowl. In this study, we quantify consumption estimates, specifically predation on fathead minnows, by age-0 and age-1 walleye reared in natural wetland basins. Six wetlands were stocked in mid-May 2001 and 2002 at a rate of 12,000 walleye fry ha^–1. Age-0 walleye were sampled bi-weekly from mid-June through mid-September 2001. Age-0 and age-1 walleye were sampled monthly from mid-May through mid-September 2002. A generalised diet shift from zooplankton to fish to macroinvertebrates was observed in 2001, whereas diets of juvenile walleye contained primarily macroinvertebrates in 2002. Stocked walleye quickly reduced fathead minnow populations in 2001 and suppression was maintained throughout 2002. Although walleye consumed primarily macroinvertebrates once prey fish populations became suppressed, consumption estimates of invertebrates by walleye were substantially less than those documented for fathead minnow populations. Thus, stocking age-0 walleye was an effective biomanipulation tool that substantially reduced fathead minnow densities and influenced lower trophic levels in these aquatic communities.