Host-parasite interaction of the myxosporeans Kudoa paniformis Kabata & Whitaker, 1981 and Kudoa thyrsites (Gilchrist, 1924) in the muscle of Pacific whiting, Merluccius productus (Ayres): an ultrastructural study

Abstract. Kudoa paniformis and Kudoa thyrsites infect the muscle of Pacific whiting, Merluccius productus , and K. paniformis is known to cause a softened muscle texture after death of the fish. Ultrastructural studies were conducted on the host-parasite interaction between Pacific whiting and these myxosporeans at two stages of their infection: (1) unencapsulated plasmodia that contained mature and developing spores, and (2) encapsulated plasmodia that contained deteriorating spores. Unencapsulated plasmodia of both species had a microvillar border that was closely associated with the host muscle. Species-specific characteristics included the presence of multi-vesicular bodies in plasmodia of K. paniformis whereas the cytoplasm of K. thyrsites plasmodia contained an array of vesicles, microfilaments and microtubules. Differences in the predominant organelles of the plasmodia may be related to the production of different proteolytic enzymes by each species. A host response became apparent only after a plasmodium had replaced the width of an infected muscle fibre. At that time, the plasmodia of both species became encapsulated by a wall of fibroblast-like cells that were connected by numerous desmosomes. Occasional phagocytes were located at the edge of these capsules. Ultrastructural evidence suggests that the encapsulated plasmodia were not proteolytically active. Melanin deposition did not occur. However, encapsulated plasmodia with deteriorating spores contained electron-dense breakdown products.     

Observations on the host-parasite relations of the Pacific whiting, Merluccius productus (Ayres), and two myxosporean parasites, Kudoa thyrsitis (Gilchrist, 1924) and K. paniformis Kabata & Whitaker, 1981

Abstract. Muscle samples from 178 Merluccius productus were examined for two myxosporean parasites, Kudoa thyrsitis and K, paniformis. Kudoa paniformis was found in 51% of the samples, while K. thyrsitis and mixed infections were observed in 7% and 17% of the samples respectively. An inflammatory response that resulted in an encapsulation around a completely replaced muscle fibre was observed in infections with either parasite. Presporogenic and sporogenic stages were common while stages that may represent early forms of the parasites were only rarely observed.     

Pacific hake (Merluccius productus Ayres, 1855) hydrolysates as feed attractants for juvenile Chinook salmon (Oncorhynchus tshawytscha Walbaum, 1792)

Soybean meal (SBM) inclusion in salmonid diets can lower feed cost, but dramatically reduces growth and feed utilization, and increases mortality in juvenile chinook salmon Oncorhynchus tshawytscha, due to diminished diet palatability and/or other adverse physiological effects exerted by antinutritional factors in SBM. The objective of this study was to investigate whether commercial Antarctic krill meal Euphausia superba or hydrolysates enzymatically produced from Pacific hake Merluccius productus could reverse the negative palatability effects of SBM inclusion in juvenile chinook salmon diets. Diets without SBM or with SBM and no added feed attractant were used as positive and negative control diets respectively. Incorporation of 2% krill meal or Alcalase^®‐produced hydrolysates into SBM‐containing diets (20% of dry matter by isonitrogenous replacement of fishmeal) significantly (P < 0.05) increased feed intake, feed utilization, fish weight gain and thermal growth coefficient during a 5‐week trial. Nevertheless, the negative effects on fish performance incurred by dietary inclusion of 20% SBM could not be fully reversed, indicating that most of those effects were likely unrelated to palatability. This study demonstrates the potential for using Pacific hake hydrolysates as a dietary feed attractant for salmonid diets, and supports the need for further research to optimize its application for ideal fish performance.     

Correlation of Kudoa Spore Counts with Proteolytic Activity and Texture of Fish Mince from Pacific Hake (Merluccius productus)

ABSTRACT

Sixteen batches of fish mince prepared using fillets from Pacific hake (Merluccius productus) harvested near Vancouver Island, Canada were studied for possible correlations of Kudoa spore counts with proteolytic activity and cooked texture. The fish were mainly infected by K. paniformis, and Kudoa spores were distributed throughout 7 sampling sites on 13 individual hake fish tested. Proteolytic activity of fish homogenate was optimum within the range of pH 5.25–5.50 and 52–55°C. Significant (p < 0.05) correlations were observed among fish mince K. paniformis spore counts, endogenous proteolytic activity, cooked texture measured as maximum compression force (g), and the change in free amino groups during autolysis.     

Effects of Varying Sucrose Concentrations in Pacific Whiting (Merluccius productus) Stabilized Mince Used for Surimi Production

Stabilized mince (SM) was made from fresh Pacific whiting mixed with varying levels of sucrose (6 to 12% w/w) including 0.2% w/w polyphosphates. SM samples were maintained in frozen storage and used at different time intervals for surimi production. Comparisons with control surimi made from fresh mince showed that acceptable surimi can be produced from SM stored at -20°C with cryoprotectant levels at 6% w/w sucrose and 0.2% w/w polyphosphates. There was a slight decrease in whiteness in surimi made from the SM samples when compared to the control. Surimi yields from SM were comparable to yields of surimi made from fresh mince.     

Comparison of Physical,Thermal and Chemical Methods to Measure Protein Denaturation in Frozen Pacific Whiting (Merluccius productus)

The potential of using the torsion test and differential scanning calorimetry (DSC) to determine the effect of frozen storage on protein denaturation in fish fillets was investigated. Pacific whiting fillets were stored for 12 weeks at three temperature conditions: -20¦C, -8¦C, and at a level varying between 0 and -8¦C. Salt soluble protein (SSP) extractability and Ca++-ATPase activity were used to evaluate the torsion test and DSC. The shear strain value of the torsion test provided a good correlation with SSP extractability, Ca++-ATPase activity, and myosin transition enthalpy as measured by DSC. Therefore, shear strain can be considered as a useful tool for the determination of protein denaturation in Pacific whiting during periods of frozen storage. Because Ca++-ATPase activity, shear stress and shear strain, and myosin transition enthalpy all decreased within one week, protein deterioration in frozen Pacific whiting appears to be rapid at the temperatures tested.     

Interannual variation in the availability and utilization of euphausiids as prey for Pacific hake (Merluccius productus) along the south-west coast of Vancouver Island

The species and size composition of euphausiids consumed by Pacific hake ( Merluccius productus ) along the south-west coast of Vancouver Island were monitored during the 1989, 1990 and 1995–97 summer feeding seasons. Thysanoessa spinifera and Euphausia pacifica were the only euphausiid species eaten by hake. Hake persisted in selecting krill longer than 17 mm and consistently preferred T. spinifera, even though there was a substantial reduction in euphausiid abundance, a change in species composition and a shift in the size distribution to smaller individuals after the 1992–93 warm water years. The biomass of euphausiids available to hake after 1993 averaged 27% of that for 1991, the pre-ENSO year, and was 12% of the 1991 value in 1996. Hake predation was not responsible for the reduction in euphausiid abundance, as it was already low at euphausiid sizes smaller than those eaten by hake.     

The feeding ecology of larval Pacific hake (Merluccius productus) in the California Current region: an updated approach using a combined OPC/MOCNESS to estimate prey biovolume

A combined optical particle counter (OPC) and multiple opening and closing net and environmental sensing system (MOCNESS) was used to obtain simultaneous measurements of the fine‐scale distribution of ‘prey‐sized’ particles and the vertical distribution of larvae of Pacific hake (Merluccius productus). Physical properties were also measured. The data were used to describe the feeding ecology of Pacific hake larvae, and to explore the effects of prey abundance, time of day, temperature and depth on feeding. Pacific hake larvae consumed a wide variety of prey including copepod eggs, nauplii, copepodites, and euphausiid metanauplii. Calanoid copepodites comprised > 75% of the ingested prey volume. First‐feeding larvae were 2.5–3.0 mm SL. These larvae consumed prey 40–200 μm wide. Larvae 3.0–6.5 mm long ingested prey 40–400 μm wide and larvae > 6.5 mm long ingested prey 400–700 μm wide. There were clear diel patterns in feeding incidence and prey volume ingested. Feeding commenced between 06:01 and 08:00 hours PST and continued until ～ 16:00 hours. Ingested prey items remained in the gut until complete gut evacuation occurred near dawn. The volume of food ingested was estimated using two indices, the cube root of the prey volume (CRPV) and the cube root of the stomach volume (CRSV). Standard length, log elapsed time since gut evacuation, depth and particle biovolume contributed significantly to variation in both indices. Temperature did not contribute to variability in either CRPV or CRSV.     

Locus-specific EPIC-PCR primers for four distinct calmodulin genes of the Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel, 1844)

International Aquatic Research - Nucleotide sequences of four distinct calmodulin genes (designated as CaM-A to -D) of the Pacific bluefin tuna (Thunnus orientalis) were compared. Nucleotide...     

Effect of temperature on the hatching success of the eggs of Japanese whiting, Sillago japonica Temminck & Schlegel, during the spawning season

Abstract. Hatching responses of the Japanese whiting, Sillago japonica Temminck et Schlegel, to a series of temperature changes were measured by exposing the fertilized eggs to eight constant incubation temperatures which ranged from 20·0 to 34·0°C. For a control, hatching temperature was kept the same as temperature of the ambient environment. Hatching responses were expressed as hatching percentages. Altogether 18 experimental trials were conducted during the natural spawning season of the species which extended over a period of 2 months from late July to mid-September 1988, when seawater temperature varied between 24·0 and 30·0°C. Optimum and limiting temperatures were recorded and the data were optimally fit to the quadratic model. Results indicated that viable hatch occurred at almost all ranges of hatching temperature from 22·0 to 32·0°C. However, no hatching was recorded at either 20·0 or 32·0°C. The experiment showed that the optimum hatching temperature varied with the ambient temperature changes during the spawning season, indicating the latter to be a dependent factor for any hatching success.     

Infection of captive Pagrus auratus (Bloch & Schneider) by the monogenean, Anoplodiscus cirrusspiralis Roubal, Armitage & Rohde (Anoplodiscidae) in Australia

Abstract The monogenean Anoplodiscus cirrtisspiralis infects the fins and nares of snapper, Pagrus auratus (Bloch & Schneider). The epidermis beneath the haptor in both microhabitats is eroded and the parasite attaches to the basement membrane by an adhesive secretion. Captive snapper suffered fin damage through high levels of infection by this parasite. Laboratory experiments showed A. cirrusspiralis to be adversely affected by reduced salinity and killed within 1 h by diluted sea water of < 5%0 salinity.     

Pathology of attachment and vascular damage associated with larval stages of Dissonus manteri Kabata, 1966 (Copepoda: Dissonidae) on the gills of coral trout, Plectropomus leopardus (Lacépède) (Serranidae)

Abstract. Tissue responses in Plectropomus leopardus gills infested with Dissonus manteri copepodid and ehalimus larvae were almost entirely proliferative, with little or no cellular infiltration. The pathological changes were related to attachment, feeding and parasite size, and comprised progressive mechanical erosion, epithelial hyperplasia and fibrosis. When present, infiltrating cells were associated with initial attachment by the copepodid and with the frontal filament basal plate. Approximately 2.4% of the respiratory area was lost as a result of direct vascular damage. Disruption of branchial blood flow resulted from the burrowing and feeding activities of the larvae and compression of adjacent vessels as the parasite increased in size. Chalimus stages were attached by a frontal filament which consisted of a stem with a terminal anchor, and a basal plate in contact with the cartilaginous filament ray. Following chalimus release, the branchial tissue appeared to repair rapidly. No frontal filament remains were found.     

Effects of food availability on feeding and growth of cultivated juvenile Babylonia formosae habei (Altena & Gittenberger 1981)

Juveniles of the scavenging gastropod Babylonia formosae habei ( Altena & Gittenberger 1981 ) were kept at different ration levels in the laboratory for 30 days. Feeding behaviour and growth performance of the juveniles in relation to food availability were studied. Babylonia formosae habei juveniles were exposed to one of the four ration levels with food provided once either every 1, 2, 5 or 10 days. Higher food consumption, longer time spent on feeding and higher percentage of feeding individuals were obtained in individuals maintained at lower ration levels. Similar growth performances were observed in individuals fed once every day or every two days. A sustained production of shell was obtained in the juveniles maintained at low ration levels. At the end of the experiment, lower protein and lipid content as well as lower energy content were measured in the somatic tissue of juveniles maintained at lower ration levels. During the 30‐day experiment, food availability is not a crucial factor on survival of juvenile B. formosae habei due to its physiological and behavioural adaptations developed in association with starvation.     

Effect of Artemia enrichment on the growth and survival of Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel) larvae

This study was carried out to investigate the suitability of Artemia enriched with docosahexaenoic acid (DHA) and choline as live food on the growth and survival rate of the Pacific bluefin tuna (PBT; Thunnus orientalis) larvae. The PBT larvae were fed either Artemia enriched with oleic acid (Diet 1), DHA (Diet 2), DHA+choline 1.0 mg L^?1 (Diet 3) and DHA+choline 2.0 mg L^?1 (Diet 4) or striped knifejaw larvae (Diet 5, reference diet), in duplicate for 12 days. Enrichment of Artemia with DHA significantly increased the DHA levels to 13.9, 13.8 and 12.5 mg g^?1 on a dry matter basis in Diets 2, 3 and 4 respectively; however, the levels were significantly lower than the reference diet (26.9 mg g^?1 dry matter basis; Diet 5). Although growth and survival rate were significantly improved by the enrichment of Artemia with DHA and choline, the improvement was negligible compared with the enhanced growth and survival rate of the fish larvae‐fed group (P<0.05). The results demonstrated that enriched Artemia does not seem to be the right choice to feed the PBT larvae perhaps because of the difficulties in achieving the correct balance of fatty acid with higher DHA/EPA from Artemia nauplii.     

Gill pathology caused by infestations of adult and preadult Dissonus manteri Kabata (Copepoda: Dissonidae) on coral trout, Plectropomus leopardus (Lacépède), (Serranidae)

Adult and preadult Dissonus manteri attached to the gills of Plectropomus leopardus cause significant pathology in the form of large hyperplastic nodules on the afferent (leading) edges of gill filaments. Nodules result from the dual actions of parasite attachment and feeding. The host response is characterized by severe epithelial hyperplasia, supplemented by fibroplasia and inflammation. Parasites attach close to the gill arch near the base of filaments. They have little effect on gill vasculature as the maxillipeds penetrate the filament superficial to the efferent filament artery and do not interfere with the blood vessels of the secondary lamellae. Tissue proliferation is limited to the wide portion of filament 'edge' epithelium in the proximal third and also does not extend to the secondary lamellae. Nodules are most numerous towards the ends of hemibranchs and are generally absent from the central regions. Leading hemibranchs bear significantly more nodules than their trailing counterparts. Of the total number of nodules, 20.5% are located on the pseudobranchs. Distribution patterns are considered to be primarily the result of D. manteri avoiding strong water currents, although this cannot explain the difference between numbers on leading and trailing hemibranchs.     

Rickettsia-like organisms in the blue-eyed plecostomus, Panaque suttoni (Eigenmann & Eigenmann)

Abstract. Intracytoplasmic organisms resembling rickettsia were observed in tissues of two blue-eyed plecostoitius, Panaqae suttoni (Eigenmann & Eigenmann), a tropical freshwater fish. Gross lesions were limited to renomegaly and splenomegaly. Cytopathological and histopathological examination of the various tissues revealed numerous small, discrete, coccoid organisms in the cytoplasm of monocytes as well as tissue macrophages of the spleen, heart, kidney and sometimes liver. Transmission electron microscopy confirmed that these organisms were within membrane-bound vacuoles and had a morphology resembling rickettsia.     

The effect of Eimeria sp. infection on the condition of blue whiting, Micromesistius poutassou (Risso)

Abstract. Eimeria sp. infection of blue whiting, Micromesistius poutassou (Risso), taken to the north and west of Scotland, was investigated with particular reference to the effect on host condition. Eimeria sp. is a parasite of the liver parenchyma and causes extensive lesions. Juvenile blue whiting were not found to be infected before the late 1-group stage, but all 308 adult (3- to 17-group) fish examined were infected. Condition factor ( k = 100 w/l³ ) showed a statistically significant decrease with increasing intensity of infection. Average value of liver weight, expressed as a percentage of total body weight, also decreased with increasing intensity of infection. It is concluded that Eimeria sp. infection is a major factor contributing to loss of condition in blue whiting from the study area. The loss of weight in fish with moderate-to-heavy infections was estimated at from 6 to 10%; this figure does not take account of mortalities resulting from Eimeria infection nor does it take account of the most heavily infected fish which could not be included in the analysis because sufficiently accurate estimates of the large numbers of oocysts present were not made.