Lernaeocera branchialis: a potential pathogen to cod ranching

A study was carried out to determine the effect of Lernaeocera branchialis on Atlantic cod infected in the laboratory and in the field and also to ascertain its effect on cod-ranching. Sixty-four percent (308) of 481 cod acquired infections in the laboratory and 33% (159) of the infected fish died over a 4-yr period. About 74% of the deaths occurred within 4 mo of the infection. Monthly samples of cod collected adjacent to a cod-ranching operation showed an initial prevalence of 30% that subsequently decreased in the following 2 mo to 15%. Prevalence of the infection also decreased among the initial field sample of cod that were kept alive, from 30 to 17% during the same 2-mo period and to 9% after 8 mo and was associated with death caused by the parasite. Cod examined at intervals after infection showed evidence of reduced weight gain, lower liver somatic index, liver lipid, and blood values than controls. A field sample taken from the same area during the summer of the following year indicated a prevalence of 12%. This higher than usual prevalence (4-6%) was associated with retention of the intermediate host, Cyclopterus lumpus, that provided an additional source of infective stages. It is likely that increased parasitism could affect the success of the cod-ranching operation in view of the parasite's devastating effects on its hosts.     

Influence of Lernaeocera branchialis (Crustacea: Copepoda) on growth rate of Atlantic cod, Gadus morhua

Influence of Lernaeocera branchialis, a hematophagous copepod, on the growth rate of Atlantic cod, Gadus morhua, was investigated in fish of various sizes. Initially, it appeared that growth, over a 16-mo period, was reduced when single or multiple infections were present. We then examined growth rate by comparing food consumption, weight gain, food conversion efficiency, and condition (k) factor over a 2-mo period and subsequently over a 4 wk in control and experimentally infected fish. Total body weight and length of each fish, controls and infected were determined before and after feeding known weights of food. Adults infected with young parasites consumed more food and gained more weight than controls, especially in the first month, but food conversion efficiency and k-factor were greater than those of controls after 2 mo, but food efficiency was still lower than in controls. In 2 groups of young infected fish, all values were consistently lower than those of uninfected fish of comparable size during the 2-mo period. Three additional trials on immature cod confirmed that infected fish consumed less food and exhibited less growth than infected controls. Our results suggest that only adult cod infected with immature parasites compensate for the infections by increasing food consumption, thus resulting in a transitory weight gain. Additionally, parasites that have completed their reproductive activities still produce subtle effects in the form of low food conversion efficiency in their hosts.     

Ultrastructural studies on the early cuticular metamorphosis of adult female Lernaeocera branchialis (L.) (Copepoda,Pennellidae)

After its final moult and fertilization an adult female of the marine fish-parasitic copepod, Lernaeocera branchialis, begins an extensive metamorphosis. This commences while the parasite is still on the flounder intermediate host and is completed once the female has established itself on the whiting final host. One early component of the metamorphosis is a considerable elongation of the parasite's abdominal region. S.e.m. and t.e.m. studies have revealed that part of the mechanism of the elongation consists of a straightening out of a highly folded abdominal cuticle. Before fertilization, the epicuticle and outer procuticular layers of this integument are thrown into a series of transverse, 4–6 µm deep pleats or folds with a density of 1–1.2 folds/µm of abdominal length. Straightening these folds can generate an approximately 6-fold length increase. The folds are already present beneath the female chalimus IV cuticle when the epidermis of this development stage starts to secrete the adult cuticle. Immediately before the final moult, the adult cuticle is super-folded with the whole cuticle displaying second-order folds, 8–10 µm deep.The capacity of Lernaeocera to engage in extensive cuticular modifications without recourse to a moult is compared with similar abilities shown by some insect species.     

The ultrastructure of the spermatozoon of Lernaeocera branchialis (Copepoda : Pennellidae)

Spermatozoa are produced by males of the fish-parasitic copepod, Lernaeocera branchialis, on the flounder (Platichthys flesus) host and packaged into spermatophores. Mature spermatozoa from spermatophores have been investigated with light microscopy and t.e.m. and s.e.m. techniques. Each is a filiform cell up to 30 µm long and 1 µm in diameter, being symmetrically tapered at each end to produce a javelin-shaped configuration. Surface s.e.m. appearances suggest that the cell is helically twisted. The spermatozoon possesses no flagellum, no nuclear envelope, no mitochondria and no orthodox acrosome. For most of its length the cell has a four-lobed appearance in transverse section and contains little more than a cylindrical sleeve of pseudomembranous material with which is associated finely filamentous or granular material which is assumed to be nuclear chromatin. The spermatozoon is immobile in seawater.The ultrastructure of L. branchialis spermatozoa has been compared with that of eight other copepod species.     

Is reduced body growth of cod exposed to the gill parasite Lernaeocera branchialis a cost of resistance?

Three hundred and sixty-nine cod Gadus morhua were individually marked and caged for 19 months. During this period, each cod was inspected several times for Lernaeocera branchialis . Growth in four groups of cod, identified by their infection history, were compared. During the caging, 79% of the cod remained uninfected, 8·5% were infected, but lost the parasite, 8% were infected with one parasite and 4·5% were infected with more than one parasite. The infected fish either harboured the parasite at caging or were infected during the study period. The highest rate of increase, both in body mass and in standard length ( L _S), was recorded in the group of male fish infected with one parasite throughout the experimental period. Conversely, those males free from infection showed significantly lower growth. The observed differences in growth could not be explained by changes in variables related to reproductive strategies. The alternative explanation for these results is that resistance to L. branchialis was associated with costs in terms of reduced growth of body mass and L _S.     

The infection dynamics and dispersion pattern of Lernaeocera branchialis L. on 0+ whiting (Merlangius merlangus L.) in the Oosterschelde (SW Netherlands)

Size and structure of the Lernaeocera branchialis population infecting 0+ whiting in the Oosterschelde were studied during 1989. Two periods of successful transmission were distinguished. The first transmission wave occurs in late spring when the post-larval whiting enter the Oosterschelde. A second wave occurs in autumn. This pattern in the infection dynamics is possibly related to seasonal variations in spatial overlap of the intermediate ( Platichthysflesus ) and the final host ( Merlangius merlangus ). The dispersion pattern of Lernaeocera branchialis within the whiting population can be described by the Poisson distribution. Possible explanations for the observed dispersion pattern are given. Evidence is presented that the rejection of pennella larvae is a key mechanism determining the abundance of L. branchialis in whiting. The potential impact of parasite-induced host mortality on population size and dispersion pattern of the parasite is discussed.     

The parasitic copepod Lernaeocera branchialis negatively affects cardiorespiratory function in Gadus morhua

The parasitic copepod Lernaeocera branchialis had a negative effect on cardiorespiratory function in Atlantic cod Gadus morhua such that it caused pronounced cardiac dysfunction with irregular rhythm and reduced stroke amplitude compared with uninfected fish. In addition, parasite infection depressed the postprandial cardiac output and oxygen consumption.     

Experimental transmission, development, and effects of a parasitic copepod, Lernaeocera branchialis, on Atlantic cod, Gadus morhua

Development and effects of adult Lernaeocera branchialis were studied following experimental transmission to Atlantic cod, Gadus morhua. Growth from the detection of pennella stages to mature adults was approximately 9-10 mo (September-June of the following year) at which time eggs were released and the adult parasites degenerated. Cod from all size groups were susceptible but the prevalence of infection was greater in small fish. Peak mortality, about 30%, occurred within 4 mo after infection and was greatest in young fish with multiple infections. Death was associated with emaciation, blood loss, open lesions, and probable occlusion of branchial blood vessels and/or ventral aorta. Infected fish, especially subadults that survived, consumed less food, gained less weight, had a lower conversion factor, and were substantially smaller than uninfected controls through a 32-wk period. Many of these fish displayed hyperactivity. Large cod that survived the infection and harboured 1 parasite were apparently unaffected but died when stressed. A previous infection conferred no protection against reinfection. Multiple infections delayed gonadal maturation and resulted in significantly lower gonadal somatic indices than in controls. Exposure of infected fish to crude oil fractions or to infection with a hemoprotozoan, Trypanosoma murmanensis, culminated in mortality, weight loss, or low organ somatic indices. It is estimated that considerable losses through mortality and weight gain in young fish occur each year in coastal areas from infections by L. branchialis, particularly in one area where it was estimated that 20% of the population was infected.     

The effects of Lernaeocera branchialis on the Merlangius merlangus population in the Medway Estuary

Whiting entering estuarine waters during autumn are largely free from the copepod Lernaeocera branchialis (L.). Infection soon follows and, between 1973 and 1975, an average 40.4% whiting were infected. The parasite's effects on fish weight over this period are assessed and, in a separate study, its effects on the host's lipid biochemistry determined. Mature adults of L. branchialis caused a significant reduction in body weight. Liver lipid content was also lower in these individuals, by more than 50%. Phospholipid levels were lower but cholesterol readings were greater in infected fish. Fatty acid composition of liver lipids appeared unaffected.     

Stage-specific mortality of Baltic cod (Gadus morhua L.) eggs

A study on cod egg mortality was carried out in the Bornholm Basin (southern central Baltic Sea) toward the end of July 1996. An initial egg aggregation marked by a satellite‐tracked drifter buoy was sampled repeatedly over an 11‐day period; profiles of temperature, salinity and dissolved oxygen were concurrently recorded. Three replicate estimates of mortality were obtained for each pair of subsequent developmental stages from newly spawned eggs to early larvae. A consistent pattern of stage‐specific mortality coincided well with previous experimental observations. Average daily mortality rates were 7.2% (eggs IA/IB), 38.7% (eggs (IB/II), 25.6% (eggs II/III), 40.0% (eggs III/IV), and 42.3% (eggs IV/early larvae). The cumulative mortality until hatch amounted to 99.9%. Results from hydrodynamic modelling, however, indicated that the drifter's trajectory was influenced by wind stress. Hence, the mortality rates might be biased despite the short sampling intervals; a modification of the sampling design is recommended for future studies.     

On differentiation of cod (Gadus morhua L.) groups in Baltic Sea

Russian Journal of Genetics - Using the AGP*, PGI-1*, PGI-2*, LDH*, IDH*, and PGM* allozyme markers, the differentiation of cod groups during the spawning period in Baltic Sea was evaluated. It was...     

First evidence of spawning of eastern Baltic cod (Gadus morhua callarias) in the Belt Sea,the main spawning area of western Baltic cod (Gadus morhua L.)

Two cod stocks (western Baltic cod, WBC, and eastern Baltic cod, EBC) are managed in the Baltic Sea which is characterized by different main spawning areas and different main spawning periods. In this study we analyse the spatial and temporal occurrence of spawning individuals of both cod stocks in the main spawning grounds of the Baltic Sea based on eight microsatellite loci. Our results suggest that EBC (Gadus morhua callarias) has formed currently temporally stable, substantially homogeneous population not only in the Bornholm Sea (ICES SD: 25) but also in the Arkona Sea (ICES SD: 24). The presented analyses proved that EBC (G. m. callarias) can temporarily also spawn in the Belt Sea.     

Experimental studies on the development of Lernaeocera branchialis (Copepoda: Pennellidae): population processes from egg production to maturation on the flatfish host

Quantitative population dynamical information derived from laboratory- and field-based experiments is provided for the fish-parasitic copepod, Lernaeocera branchialis, infecting flounder (Platichthys flesus) and whiting (Merlangius merlangus). Adult, post-metamorphosis females from whiting can produce more than one set of egg-strings. The mean number of eggs in each egg-string pair was 1445. At 10 °C these eggs took about 12.7 d after extrusion before hatching of NI nauplii began. Hatching took up to 12 days to be completed with an exponentially declining pattern of output over this period. In the laboratory about 44% of the egg-string egg population successfully passed through the NI to NII nauplius moult and the NII to copepodid moult to produce infective copepodids, a process lasting about 2 d. The non-feeding copepodids had a maximum survival time at 10 °C of 18 d, with a time to 50% survival of 7.5 d. In laboratory infection experiments at 10 °C, copepodids infected flounder and passed through all their developmental stages to adulthood and copulation in a minimum of 25 d. Field experiments on the seabed off Lowestoft in June 1987 with a sea temperature of about 16 °C suggested that the developmental period in those conditions could be as short as 11 d. Previously uninfected flounder in the field experiments became naturally infected with copepodids at a mean rate of not less than 30 parasites per fish d^–1.     

Prevalence and influence of Loma branchialis (Microspora) on growth and mortality in Atlantic cod (Gadus morhua) in coastal Newfoundland

A study was conducted to determine the prevalence, geographical distribution, and effects of a microsporan parasite, Loma branchialis, in Atlantic cod in coastal Newfoundland. The parasite was identified microscopically as opaque, ovoid xenomas, primarily in the gills, heart, and spleen. Although widely distributed in young fish inhabiting 7 coastal localities, prevalence was 1-7% in general, <0.01% in older and large fish, but 78% in market-size cod from a commercial farm. Some of the latter fish were emaciated, and approximately 2 mo after the parasite was detected, 63% succumbed with a massive infection. Condition factor and blood values were significantly lower than those in reference fish. An experimental study conducted over 2 yr revealed that mass gained and condition factor were significantly lower in infected cod than in controls at the termination of the study. Feed consumption, mass gained, feed conversion efficiency, and condition factor also were significantly lower in another group of infected cod of marketable size studied over 12 wk. Xenomas also were observed in the heart and gills of year class II cod reared in a hatchery. Loma branchialis is considered to be a potential pathogen in both hatchery-reared and net pen-cultured cod in Newfoundland.     

Sexual maturation of cod (Gadus morhua L.) in the southern Baltic (1990–2006)

Baltic cod, like other species, is susceptible to inter‐annual fluctuations in sexual maturation, depending on the length, age, sex, extent of the habitat area, and stock abundance of the cod population. Maturity is one of the biological indicators used to detect changes in a stock that can be caused by fishing. To address these issues specifically for the eastern Baltic cod stock, long‐term data (1990–2006) from Polish research vessels in the southern Baltic were examined. To date, the ICES has used the same maturity ogives over extended periods and assumed invariant sex ratios for the assessment of eastern Baltic cod. The combined maturity ogives calculated in the present study were markedly lower, particularly for age groups 2–4 (5), in all periods, than those used in the ICES assessment. Moreover, the proportion of females increased with length and age, suggesting that annual verification of the sex ratio is needed. The present study also revealed that the total length (L_50%) and the age (mean age‐at‐maturity; MAM_50%) at which 50% achieved first sexual maturity were higher for females than for males in the study period. The long‐term mean L_50% and MAM_50% for females were 43.9 cm and 4.3 years, respectively, and for males 34.8 cm and 3.4 years. There was also a spatial difference between calculated maturity ogives, with slightly lower L_50% (range: 1.4–8.6 cm) in the Gdańsk Basin than in the Bornholm Basin. The increasing trend in fishing mortality observed in 1993–2004 (ICES data) did not translate into a temporal trend in calculated maturity ogives. However, changes in L_50% and MAM_50% reflected recruitment variations (ICES data). The significance of these findings is discussed in the context of the environment and recruits abundance.     

Robertsonian polymorphism in plaice, Pleuronectes platessa L., and cod, Gadus morhua L., (Pisces Pleuronectiformes and Gadiformes)

Karyotypic analysis of plaice, Pleuronectes platessa L., and cod, Gadus morhua L., revealed that the chromosome numbers in both species vary but that chromosome arm numbers (NF) stay constant. The C-, Q- and R-banding patterns also confirmed that the population of plaice studied shows Robertsonian polymorphism. The tendency of reduction in chromosome number in fishes suggests that Robertsonian fusions play a role in karyotype evolution in fishes.     

Effect of concurrent infections of Lernaeocera Branchialis (Copepoda) and Trypanosoma murmanensis (Protozoa) on Atlantic cod, Gadus morhua

A study was initiated to ascertain the prevalence, effect and interaction of the adult stages of the parasitic copepod, Lernaeocera branchialis, on Atlantic cod concurrently infected with a hematozoan, Trypanosoma murmanensis, by comparing condition (K) factor, organ somatic indices, hematological values and lipid concentrations of the liver from infected and uninfected fish of comparable length. Prevalence of the copepod varied from 9 to 21% and was highest in fish examined on the southern coast of Newfoundland. Body condition and blood values were significantly lower in young cod infected with two parasites whereas only K-factor was altered in two size classes parasitized by one copepod. Although lipid concentrations were similar in three length groups of fish without and infected with L. branchialis, the pooled values were significantly greater among the infected group. Mortality occurred only in juvenile cod infected with the copepod and T. murmanensis concurrently. Cod which survived dual infections had lower K-factor and blood values than controls or fish harboring single, parasitic infections. It is concluded that an infection with an adult L. branchialis does not impair the health of fish in this area of the northwestern Atlantic Ocean, but the presence of T. murmanensis concurrently can potentiate its effect.     

Ecological implications of Echinorhynchus gadi parasitism of Baltic cod (Gadus morhua)

Of 533 Baltic cod (body length 21–93 cm) 530 were infected with Echinorhynchus gadi at infection intensities from 1 to 490 per host. The heavy infection of large cod (normally not feeding on amphipods) may be explained by a transfer of parasites from prey fishes to the predating large cod.     

Distribution patterns of Baltic herring larvae, Clupea harengus L., in the coastal waters off Helsinki, Finland

Changes in the spatial distribution of Baltic herring larvaethrough time were investigated in the waters off Helsinki, thenorthern Baltic Sea. The average larval densities were comparableto the relatively low levels (mean around 2 larvae m^–2)found in other studies in the Gulf of Finland. In shallow baysvirtually no herring larvae were found in early June. In lateJune and early July the densities of larvae longer than 10 mmincreased to 1–4 larvae m^–2 in shallow areas (depth<2 m), i.e. to levels higher than those recorded in deeperwaters. In combination with data on the size distributions ofthe larvae, these observations suggest that a significant proportionof the herring larvae are found in shallow water after the yolksac stage. We conclude that shallow coastal waters are potentiallyimportant nursery areas for herring larvae and that this featureof herring larval biology should be taken into account in planningsampling programs for larval herring.