Ichthyophonus infections in cultured marine fish from Spain

Ichthyophonus sp. is reported for the first time in Mugil capito (thinlip grey mullet) and Li a saliens (leaping grey mullet). The fungus was also found in L. aurata (golden grey mullet), Dicentrarchus labrax (sea bass), Sparus aurata (gilthead sea bream) and Scophthalmus maximus (turbot), whereas Mugil cephalus (grey mullet) was not parasitized. In fish sampled periodically, the highest prevalences were observed in sea bass and the lowest in turbot. Among the fish sampled occasionally, the fungus was found associated to an epizootic in thinlip grey mullet. Ichthyophonus was never found in fish weighing <0·5 g. An increase in the prevalence of infection with the age of turbot and gilthead sea bream was observed. Gilthead sea bream and sea bass showed higher prevalences in a closed system than in open and semi-intensive systems. Multinucleate spherical spores, hyphae and endospores of Ichthyophonus sp. parasitized different organs of thinlip and leaping grey mullets, though infection intensity was maximal in the spleen. In the remaining fish, the fungus was found mainly in the trunk kidney, where it appeared frequently in a necrotic form. Ichthyophonus sp. can be considered a potential threat for marine fish aquaculture, especially in culture conditions which may favour the introduction and transmission of the fungus.     

Mineral nutrition of haddock Melanogrammus aeglefinus(L.): a comparison of wild and cultured stock

The macro and trace mineral composition of vertebrae and muscle in wild and cultured haddock Melanogrammus aeglefinus was determined. Results indicated that haddock deposit c . 10% higher amounts of mineral than salmonids. Based on distribution between the analysed tissues as well as concentration differences, the minerals in wild and cultured haddock were divided into four categories: (1) As, Mn, Na, S and Zn concentration did not show any significant ( P  > 0·05) variation in both muscle and vertebrae; (2) Cr, Co, Mg, Mo and Si concentrations in wild and culture stocks muscle did not vary but vertebrae concentration showed significant differences ( P  < 0·05); (3) Ca and Cu concentration varied in muscle while remaining the same in vertebrae; (4) Al, Ba, Fe, P, K and Sr concentration showed a significant difference in both muscle and vertebrae. Vertebrae P content of cultured haddock was lower than that of wild fish whereas muscle P content was relatively high in cultured fish. Vertebrae and muscle Fe content of cultured haddock was significantly higher than in wild fish. The Mg, K, Co and Cr concentrations in vertebrae were significantly higher in wild haddock than in cultured fish, whereas Mo and Al levels were low. These differences in trace element composition of wild and cultured haddock were probably related to differences in food source and therefore the mineral composition of the diet. The nutritional significance of these findings is discussed.     

Temporal stability of sea louse Lepeophtheirus salmonis Krøyer populations on Atlantic salmon Salmo salar L. of wild, farm and hybrid parentage

Atlantic salmon salmo salar smolts of wild, hybrid and farmed parentage were individually tagged then reared in a sea cage for 8 months. The fish were sampled three times during this period. On all occasions, farmed Atlantic salmon displayed the highest abundance and density of sea lice Lepeophtheirus salmonis , whilst no significant differences were observed between hybrid and wild Atlantic salmon. Percentage variation between the lowest and highest infected groups was as high as 175 and 144% for L. salmonis abundance and density respectively (sample 2). The temporal stability of interindividual sea lice infection levels was investigated pair‐wise between samples using correlation (sample 1 v . 2, 1 v . 3 and 2 v . 3). When calculated using sea louse abundance, correlations ranged from r ² = 0·11, P  < 0·01 to r ² = 0·39, P  < 0·001, but, when the effects of fish size were controlled for by converting abundance to density, all correlations were <  r ² = 0·1. Therefore, these data indicate that a fish's relative infection level in one sample was a weak predictor of its relative infection level in another sample. This suggests that identification of individual Atlantic salmon that display reduced susceptibility to sea lice, may be problematic.     

Thermally induced phenotypic plasticity of swimming performance in European sea bass Dicentrarchus labrax juveniles

The vulnerability of embryonic and larval stages of European sea bass Dicentrarchus labrax to environmental temperature and the longer-term consequences for the early juveniles was demonstrated. This phenotypic plasticity was highlighted by subjecting D. labrax at 15·2 ± 0·3 or 20·0 ± 0·4° C (mean ± s . d .) up to metamorphosis and then at the same temperature (18·5 ± 0·7° C). After 4–6 weeks at the same temperature, the measurement of critical swimming speed at four exercise temperatures (15, 20, 25 and 28° C) showed a significantly higher swimming capacity in the fish initially reared at 15° C than for fish initially reared at 20° C. This performance was correlated with significant differences in the phenotype of red muscle. Thermally induced phenotypic plasticity was clearly demonstrated as an important mechanism controlling swimming performance in early juveniles of D. labrax .     

Climate variables and spawning migrations of the striped mullet and white mullet in the north‐western area of the Gulf of Mexico

The 'smoothed'(4253e HT smoother) 6 year time series with a monthly periodicity of catches (where the increases of the catches reflect the spawning migration) of Mugil cephalus and Mugil curema , were correlated (Pearson correlation index) against the 'smoothed' data on rainfall, water temperature, daylight and tide monthly averages. Water temperature and M. curema spawning migrations had a negative correlation ( r  = −0·77), while tide monthly averages and M. cephalus spawning migrations were positively correlated ( r  = 0·84). The two environmental variables that showed highly significant correlations were water temperature and daylight ( r  = 0·85, P  < 0·05). Meteorological tides were used as a reflection of the effect of the north winds from the Gulf of Mexico which produce an average tide rise from September to November. The relationship of these variables with spawning migrations is discussed, and it is suggested, in particular, that meteorological tides, as a reflection of the north winds, are the trigger (zeitgebers) for M. cephalus spawning in the ocean.     

In vitro interactions between Neoparamoeba spp. and salmonid leucocytes; the effect of parasite sonicate on anterior kidney leucocyte function

Sonicated Neoparamoeba spp. (Nspp) did not affect the in vitro respiratory burst response of leucocytes isolated from Atlantic salmon Salmo salar , rainbow trout Oncorhynchus mykiss and chinook salmon Oncorhynchus tshawytscha anterior kidneys ( P > 0·05). Atlantic salmon and chinook salmon leucocytes pre-incubated with the parasites, however, responded to phorbol myristate acetate (PMA) stimulation with a greater response compared to cells incubated with PMA on its own ( P < 0·05). Sonicated Nspp was not chemo-attractive for anterior kidney leucocytes isolated from all three fish species.     

Effect of feeding level and feeding frequency on specific dynamic action in Silurus meridionalis

The effect of feeding level ( F _L; 0·5 to 4% dry diet mass per wet fish body mass) and feeding frequency (once every 4 days to twice per day) on postprandial metabolic response was investigated in southern catfish Silurus meridionalis at 27·5° C. The results showed that there was no significant difference in the specific dynamic action (SDA) coefficient among the groups of different feeding levels ( P  > 0·05). The duration increased from 26·0 to 40·0 h and the peak metabolic rate increased from 207·8 to 378·8 mg O₂ kg⁻¹ h⁻¹ when the feeding level was increased from 0·5 to 4%. The relationship between the peak metabolic rate ( R _P, mg O₂ kg⁻¹ h⁻¹) and F _L could be described as: R _P = 175·4 + 47·3 F _L( r ² = 0·943, n  = 40, P  < 0·001). The relationship between the SDA duration ( D , h) and F _L could be described as D =30·97 F _L^0·248 ( r ²=0·729, n =40, P  < 0·001).     

Light and Electron Microscopic Description of Sphaerospora dicentrarchi N. Sp. (Myxosporea: Sphaerosporidae) from Wild and Cultured Sea Bass, Dicentrarchus labrax L.

ABSTRACT. A new myxosporean, Sphaerospora dicentrarchi n. sp., was found in numerous organs of wild and cultured sea bass ( Dicentrarchus labrax L.). It is distinguished from all previously reported Sphaerospora spp. by the shape and small size of the spores, location in the host and its geographical distribution. Prevalence of infection was 100% and 83.5% in wild and cultured fish, respectively. Outstanding ultrastructural features are the presence of a binucleate sporoplasm, valvogenic spheroidal structures and capsulogenic lipid inclusions. Other data concerning ultrastructure and sporogenesis are presented.     

Intraspecific aggression in rosyside dace, a drift-feeding stream cyprinid

Individual rosyside dace Clinostomus funduloides in a semi-natural, artificial stream displayed substantial differences in their aggressiveness and could be classified as: (1) non-aggressive (NA, 18 of 30 rosyside dace), (2) moderately aggressive (MA, 9 of 30) and (3) highly aggressive (HA, 3 of 30). Rosyside dace groups, however, did not exhibit linear dominance hierarchies and fish size was only weakly correlated with the number of aggressive acts performed per individual. Small rosyside dace (<56 mm L_F) were always non-aggressive, but larger fish were present in all three aggression classes. The difference in size between the contestants was significantly, although not very strongly, correlated with the probability of winning an agonistic interaction (r ²=0·39). Aggressive rosyside dace may have ultimately gained higher fitness than less aggressive ones. HA individuals occupied the upstream-most position within foraging groups significantly more often than other rosyside dace. This location should be the most profitable one because its occupant will be the first to encounter prey. HA rosyside dace also occupied significantly higher focal velocities that were closer to energetic optima than MA and NA ones. They also had greater foraging rates and were less solitary than less aggressive fish, but these differences only were significant at the P=0·066 and P=0·081 level, respectively. Finally, HA fish performed significantly more aggressive acts and feedings backwards than other individuals. Despite these differences, the effects of intraspecific aggression in rosyside dace appeared less substantial than those that have been observed in stream salmonids.     

Isolation by distance and selection effects on genetic structure of sardines Sardina pilchardus Walbaum

Allozyme data were used to analyse the genetic structure of Sardina pilchardus populations. Fifty samples from 15 locations between the North Sea and Mauritania, including samples from the Azores, Madeira and the Mediterranean Sea, were surveyed. A weak but significant structure was found between all samples ( F _ST= 0.057, P < 0·001). This structure results from a change in the most common allele of SOD* between the North African and the Azores populations separated by the greatest distance. This locus seemed to be under selective pressure according to the test of neutrality, and the variations in allele frequencies may be explained due to isolation by distance (IBD) of coastal populations (from Mauritania to the North Sea) ( r = 0·86, P < 0·001). When SOD* was removed from the analyses, IBD was not observed in coastal populations ( r = 0·236, P > 0·05) but was observed over the whole range ( r = 0·321, P = 0·05). The genetic structure of S. pilchardus is driven by both IBD and selective processes.     

Feeding ecology and habitat preferences of the catfish genus Trichomycterus in low‐order streams of the Colombian Andes

Six lower order streams in the south‐west of Colombia were sampled on a monthly basis in order to determine the status of Trichomycterus species in relation to their food supply (macroinvertebrates), and physico‐chemical habitat. Fishes were sampled by electrofishing and samples taken for dietary analysis. Macroinvertebrates were collected using a Surber sampler. Trichomycterus spp. populations were present in all streams in habitats ranging from soft to hard substrata and from relatively stagnant waters to fast flowing streams. The average density of the fishes ranged from 0·06 to 1·14 individuals m⁻² with peaks in population corresponding to recruitment of individuals of <1 g. Trichomycterus spp. were found to be benthic carnivores with a diet mostly of aquatic insects. The index of relative importance for the dietary items was 35·0, 10·5, 1·9 and 7·8% for Chironomidae, Trichoptera, Ephemeroptera and Oligochaeta respectively. Combined with physical habitat data, ordinations of fishes and macroinvertebrate data suggested that differences in abundance among sites were driven by stream size and flow regime, indicating dominance of the physical habitat, although a high correlation between Trichomycterus spp. and Chironomidae abundances ( r  = 0·81, P  = 0·049) was also recorded.     

Energy savings in sea bass swimming in a school: measurements of tail beat frequency and oxygen consumption at different swimming speeds

Tail beat frequency of sea bass, Dicentrarchus labrax (L.) (23.5 ± 0·5 cm, L_T ), swimming at the front of a school was significantly higher than when swimming at the rear, for all water velocities tested from 14·8 to 32 cm s⁻¹. The logarithm of oxygen consumption rate, and the tail beat frequency of solitary swimming sea bass (28·8 ± 0·4 cm, L_T ), were each correlated linearly with swimming speed, and also with one another. The tail beat frequency of individual fish was 9–14% lower when at the rear of a school than when at the front, corresponding to a 9–23% reduction in oxygen consumption rate.     

Genetic differentiation among populations of the shortfinned eel Anguilla australis from East Australia and New Zealand

Variability at seven microsatellite loci was used to survey the genetic population structure of the shortfinned eel Anguilla australis . Samples were collected from six estuaries along the east coast of Australia and from three estuaries around New Zealand. Hierarchical analysis of molecular variance of the five loci with good fit to Hardy–Weinberg genotypic proportions detected highly significant differences among samples ( F _ST= 0·016, P < 0·001). The fixation index between countries ( F _CT= 0·012, P < 0·001) was more than double the index among samples within countries ( F _SC= 0·005, P < 0·05). An unweighted pair-group method with arithmetic mean (UPGMA) tree also supported the separation of Australian and New Zealand populations, as did assignment tests, which correctly assigned 80 and 84% of the individuals to Australia and New Zealand, respectively. Isolation-by-distance appeared among samples overall ( r = 0·807, P < 0·001), but not among samples within countries ( r = 0·027, P > 0·05 in Australia; r = 0·762, P > 0·05 in New Zealand). These findings indicate that populations of A. australis in East Australia and in New Zealand may be reproductively isolated from one another. Genetic differentiation among populations of A. australis was two- to 10-fold higher than that among populations of other temperate eels in the North Atlantic Ocean, suggesting that two group of A. australis may reflect sub-species. Anguilla australis in the two countries have different genetic structures and thus require separate management. Genetic isolation between Australian and New Zealand populations indicates that juveniles recruit independently into these two regions from geographically or temporally isolated spawning areas.     

Effect of acute and chronic ammonia and nitrite exposure on oxygen consumption and growth of juvenile big bellied seahorse

Juvenile big bellied seahorse Hippocampus abdominalis were exposed acutely and chronically to elevated ammonia and nitrite {24 h exposure: 0·01, 5·0, 10·1, 14·8 and 19·9 mg l⁻¹ total ammonia-nitrogen [TA-N] and <0·001, 74·4, 99·2 and 123·6 mg l⁻¹ [NO₂-N] nitrite-nitrogen and 35 days exposure: 0·11, 0·55, 1·67 and 3·07 mg l⁻¹ TAN and <0·001, 0·92, 4·67 and 9·10 mg NO₂-N l⁻¹}. Significant ( P <0·001) increases in oxygen consumption rate and ventilation frequency occurred at 14·8, 19·9 mg l⁻¹ TA-N and 99·2, 123·6 mg l⁻¹ NO₂-N for acutely exposed fish. Oxygen consumption rate was significantly ( P <0·05) elevated at 1·67 and 3·07 mg l⁻¹ TA-N in chronically treated fish and ventilation frequency increased significantly ( P <0·05) at 0·55, 1·67, 3·07 mg l⁻¹ TA-N and 4·59, 9·10 mg l⁻¹ NO₂-N. There were no significant differences in growth between controls and ammonia exposed fish. Mortalities occurred at 14·8, 19·9 mg l⁻¹ TA-N.     

Comparison of phospholipid and fatty acid composition of wild and cultured striped bass eggs

The dominant fatty acids in all neutral lipid fractions of non-water hardened eggs from two wild and one cultured stock of striped bass Morone saxatilis were the monoenes, 18 : 1n9/n7>16 : 1n7>17 : 1. The dominant fatty acids in the phospholipid fraction of all eggs, regardless of origin, were 22 : 6n3>18 : 1n9/n7>20 : 5n3>16 : 1n7>16 : 0>18 : 0. Arachadonic acid (AA, 20 : 4n6) was significantly lower (2·0%) in cultured fish eggs compared to either wild stock (5·8–6·1%). Fatty acids from the liver and eggs of wild Shubenacadie fish were similar to one another with respect to both neutral and phospholipid fractions. However, the AA and eicosapentaenoic acid (EPA, 20 : 5n3) content of the phospholipid fraction varied according to the hypothesized migration behaviour of Shubenacadie fish. The total lipid content of wild fish eggs was significantly greater than that of cultured fish. The total phospholipid content of Shubenacadie eggs was significantly higher than either Roanoke or cultured fish eggs. Phosphotidylinositol (PI) was the dominant phospholipid found ins all egg samples from all origins as opposed to phosphotidylcholine, which is usually the dominant phospholipid. These data indicate that PI and AA may have important and as yet unidentified roles in fertilization and embryonic development in these fish.     

Nitrogen and phosphorus content of some temperate and tropical freshwater fishes

The nitrogen and phosphorus content of two temperate fishes, Rutilus rutilus and Perca fluviatilis , and six tropical fishes, Oreochromis niloticus , Cichla monoculus , Serrassalmus rhombeus , Plagioscion squamosissimus , Prochilodus brevis and Hoplias malabaricus , were investigated to test the hypothesis that variation in body P content and N:P ratio is related to body size. Regressions of %P and N:P ratios against fish size (length and mass) confirmed the hypothesis for P. fluviatilis and P. squamosissimus , suggesting that body size is an important factor driving body P content and N:P ratios in some fishes. Moreover, significant increases in %N and N:P ratio with body size was found for H. malabaricus , a common piscivorous fish of the Neotropics. Interspecific variation in %P and N:P ranged two-fold and significant differences ( P < 0·05) were found among the tested species. The mean ± s . d . elemental content across all fishes ( n = 170) was 10·35 ± 1·29% for N and 3·05 ± 0·82% for P, while the N:P ratio was 8·00 ± 2·14. Data on fish body nutrient content and ratio will improve parameterization of bioenergetics and mass balance models and help clarify the role of fishes in nutrient cycles in both temperate and tropical freshwaters.     

Feeding preference and deterrence in rabbitfish Siganus fuscescens for the cyanobacterium Lyngbya majuscula in Moreton Bay, south‐east Queensland, Australia

Rabbitfish Siganus fuscescens preferences for Lyngbya majuscula collected from three bloom locations in Moreton Bay, Queensland, Australia, were tested along with a range of local plant species in the laboratory. Consumption of L. majuscula by fish did not differ between wild and captive‐bred fish ( P  = 0·152) but did differ between bloom location ( P  = 0·039). No relationship was found between consumption rates and lyngbyatoxin‐a concentration ( r ² = 0·035, P  = 0·814). No correlation existed between C : N and proportion of food consumed when all food types were analysed statistically, whereas a clear correlation was observed when L. majuscula was removed from the calculations. In simulated bloom conditions, fish avoided ingestion of L. majuscula by feeding through gaps in the L. majuscula coverage. Both wild and captive‐bred S. fuscescens showed a distinct feeding pattern in 10 day no‐choice feeding assays, with less L. majuscula being consumed than the preferred red alga Acanthophora spicifera . Lyngbya majuscula however, was consumed in equal quantities to A. spicifera by wild S. fuscescens when lyngbyatoxin‐a was not detectable. Wild fish probably do not preferentially feed on L. majuscula when secondary metabolites are present and are not severely impacted by large L. majuscula blooms in Moreton Bay. Furthermore, poor feeding performance in both captive‐bred and wild S. fuscescens suggests that they would exert little pressure as a top‐down control agent of toxic L. majuscula blooms within Moreton Bay.     

Mycobacteriosis in wild rabbitfish Siganus rivulatus associated with cage farming in the Gulf of Eilat, Red Sea

Infection patterns of Mycobacterium marinum were studied over a period of 3 yr in wild rabbitfish Siganus nivulatus populations associated with commercial mariculture cages and inhabiting various sites along the Israeli Red Sea coastline. Mycobacteriosis was first recorded from the Red Sea in 1990 in farmed sea bass Dicentrarchus labrax and is absent from records of studies on parasites and diseases of wild rabbitfish carried out in the 1970s and 1980s. A sharp increase in the prevalence of the disease in cultured and wild fish in the region has occurred since. A total of 1142 rabbitfish were examined over a 3 yr period from inside mariculture net cages, from the cage surroundings and from several sites along the coast. Histological sections of spleens were examined for presence of granulomatous lesions. Overall prevalence levels of 50% were recorded in the rabbitfish sampled inside the net cages and 39% at the cages' close surroundings, 21% at a sandy beach site 1.2 km westwards, 35% at Eilat harbour 3 km to the south and 42% at a coral reef site about 10 km south of the cages. In addition, 147 fish belonging to 18 native Red Sea species were sampled from 2 sites, the net cage farm perimeter and the coral reef area, and examined for similar lesions. None of those from the coral reef were infected with Mycobacterium; however, 9 of 14 species collected from the cage surroundings were infected. An increase in prevalence of mycobacteriosis in the mariculture farm area was noted from 1995 to 1997. At the same time, a significant increase in prevalence was also apparent at the coral reef sampling site. Two M. marinum isolates from rabbitfish captured at Eilat harbour and the coral reef site were shown by 16S rDNA sequencing analysis to be identical to isolates from rabbitfish trapped inside the mariculture cages as well as isolates from locally cultured sea bass D. labrax. The implications of spreading of M. marinum infection in wild fish populations in the Gulf of Eilat are discussed.     

Temporal repeatability of relative standard metabolic rate in juvenile Atlantic salmon and its relation to life history variation

There was a strong correlation between the relative standard metabolic rate (rSMR) values of individual Atlantic salmon Salmo salar L. measured 5 and 22 weeks after first feeding in June and October respectively (Pearson's r =0·68, 26 d.f., P <0·001). However, this is a conservative estimate of repeatability as two separate regressions were used to calculate SMR in October due to the separation of the population into an upper modal group made up of early migrants and a lower modal group comprised of delayed migrants. SMR values in June and October were similar (paired t test, t =-0·85, 27 d.f., P >0·05) when expressed as the percentage deviation from those predicted for a fish of that size based on the body mass/SMR relations in June or October indicating that relative standard metabolic rates were stable over time when food was not limiting. rSMR status was maintained in 19 of the 28 fish (i.e. 68%) between the two measures. rSMR status was correlated with life history strategy: salmon fry with a high SMR in June were more likely to become smolts during the autumn than those with a low SMR.     

Cyclic feeding and subsequent compensatory growth do not significantly impact standard metabolic rate or critical swimming speed in rainbow trout

Standard metabolic rate ( R _s) and critical swimming speed ( U _crit) were used to assess the aspects of physiological status (stamina) of rainbow trout Oncorhynchus mykiss . Fish were fed either 1·5% body mass daily, 1·5% body mass cyclically (3 weeks of food deprivation followed by 3 weeks of refeeding), a ration based on Stauffer's formula (a maximum temperature-specific ration level) daily or on Stauffer's ration cyclically for 18 weeks. It was hypothesized that if cyclic feeding had no impact on the status of the fish, R _s and U _crit would not cycle with the feeding regime. This hypothesis was supported. No significant difference was found between the mean mass and the fork length of the four groups at the end of the experiment ( P > 0·05). Feeding had no effect on changes in R _s among the four groups, which were significantly different throughout the experiment ( P ≤ 0·05). No significant difference in U _crit was found ( P > 0·05) until at week 12 between groups fed 1·5% body mass ration cyclically and Stauffer's ration daily ( P ≤ 0·05). For groups fed a 1·5% body mass ration cyclically and daily, significant differences occurred at week 15 ( P ≤ 0·05) but no significant difference was found by week 18 ( P > 0·05), suggesting that cyclic feeding does not affect the aspects of physiological status (stamina) of the fish.