Foraging and breeding performance of Japanese cormorants in relation to prey type

Seabirds are high trophic predators in marine ecosystems and are sensitive to change in food supply and thus seabirds can be used as monitors of the marine environment. In order to study the foraging responses of Japanese cormorants Phalacrocorax filamentosus breeding at Teuri Island, Hokkaido to changes in fish availability, the diet was assessed from the regurgitations of parents and chicks, and diving behavior was measured by using time-depth recorders. Breeding performance (brood size, chick growth, breeding success) was monitored using conventional methods to study their breeding responses. Japanese cormorants changed the diet and foraging behavior over four summers. The birds fed mainly on epipelagic schooling fish when they were available and on demersal fish when pelagic fish availability was low. They tended to dive deeper and longer in a year when they fed mainly on demersal fish than the other years, reflecting the change in the depth distribution of prey fish. Chick growth rate did not differ among years, but fledging success was lower in the years of demersal fish as their meal delivery rate was low. When epipelagic schooling fish were considered scare, parents maintained chick growth by reducing brood size. High variability and unpredictability in pelagic fish abundance are key factors affecting the foraging and breeding performance of Japanese cormorants, which could potentially be used to monitor fish resources.     

Fish as sources and sinks of nutrients in lakes

1. The release of total phosphorus (TP) and nitrogen (N in ammonium) was measured for the five most abundant fish species (>85% of biomass) in Mouse and Ranger Lakes, two biomanipulated, oligotrophic lakes in Ontario. 2. The specific release rate of both nutrients was significantly related to fish mass; log₁₀ TP release rate (μg h^?1) = 0.793 (±0.109) [log₁₀ wet mass (g)] + 0.7817 (±0.145), and log₁₀ N release rate (μg h^?1) = 0.6946 (±0.079) [log₁₀wet mass (g)] + 1.7481 (±0.108). 3. When fish nutrient release was standardized for abundance (all populations, 1993–95) and epilimnetic volume, fish were estimated to contribute 0.083 (±0.061) μg TP L^?1 day^?1, and 0.41 (±0.17) μg N L^?1 day^?1 in Mouse L., and 0.062 (±0.020) μg TP L^?1 day^?1 and 0.31 (±0.08) μg N L^?1 day^?1 in Ranger L. 4. In comparison, concurrent rates of total planktonic P regeneration were 1.02 (±0.45) μg L^?1 day^?1 (Mouse L.) and 0.85 (±0.19) μg L^?1 day^?1 (Ranger L.). Fish represented 8% of planktonic P release in Mouse L. and 7% in Ranger L. 5. Fish dry mass had mean elemental body compositions of 39.3% carbon, 10.9% nitrogen, and 4.0% phosphorus (all fish combined), with a mean molar C : N : P ratio of 27 : 6 : 1. This comprised about 55% and 23% of the total epilimnetic particulate P and N respectively. 6. Turnover times of P and N in fish were approximately 103 and 48 days respectively. In comparison, planktonic turnover times of particulate P in Mouse and Ranger Lakes were 4.3 and 4.4 days respectively. Given their high P content and low turnover rates, fish appear to be important P sinks in lakes.     

Seagrass feeding choices and digestive strategies of the herbivorous fish Sarpa salpa

This is the first study investigating the plant–herbivore interaction between Sarpa salpa, which has overgrazed seagrass transplants in Portugal, and the seagrasses Cymodocea nodosa, Zostera marina and Zostera noltii, which have been considered for restoration. When offered the choice between the three seagrasses in outdoor tanks, adult S. salpa clearly preferred Z. noltii. Testing the seagrasses separately, mean ± s.d. feeding rates ranged from 21 ± 11 g seagrass fresh mass kg^?1 fish mass day^?1 for Z. marina to 32 ± 9 g seagrass fresh mass kg^?1 fish mass day^?1 for C. nodosa and 40 ± 11 g seagrass fresh mass kg^?1 fish mass day^?1 for Z. noltii (temperature = 16° C). Food‐processing rate in S. salpa did not differ between seagrasses, and there was no evidence of a regulation of processing rate according to food intake. Seagrasses differed substantially in nitrogen content and C:N, with C. nodosa containing the highest nitrogen content and lowest C:N (2·5 ± 0·1% and 14·0 ± 1·0), followed by Z. noltii (2·1 ± 0·1% and 17·0 ± 1·0) and Z. marina (1·4 ± 0·1% and 26·0 ± 2·0). Food‐processing rate in S. salpa and the nutritional value of the seagrasses were not correlated with the observed feeding preference and rate. The study suggests that C. nodosa and Z. marina are less at risk of overgrazing by S. salpa and might thus be preferable to Z. noltii for seagrass restoration in areas with noticeable abundances of this fish.     

Sexual differences in the diet of great cormorants <Emphasis Type="Italic">Phalacrocorax carbo sinensis</Emphasis> wintering in Greece

Sexual differences in the diet of the great cormorant, Phalacrocorax carbo sinensis, were studied in four Greek wintering areas, the Amvrakikos Gulf, the Axios and Evros Deltas and the Messolonghi Lagoon, through the analysis of stomach contents. Great cormorants are birds sexually dimorphic in size, with males being generally larger than females. Although similar prey species were found in the stomachs of both sexes in all the studied areas, significant differences were observed with respect to the proportion of species taken. Male birds ate higher proportions of large fish species such as grey mullets, European sea bass, Dicentrarchus labrax, and Prussian carp, Carassius gibelio, while female birds took higher proportions of smaller species such as big-scale sand smelt, Atherina boyeri, and black goby, Gobius niger. As a consequence, male great cormorants were found to feed on significantly larger prey than did females by means of fish standard length and body mass. There was no significant difference between the sexes in the mass of food found in stomachs.     

Stressor interactions in freshwater habitats: Effects of cold water exposure and food limitation on early‐life growth and upper thermal tolerance in white sturgeon,Acipenser transmontanus

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Differences in growth between offspring of anadromous and freshwater brown trout Salmo trutta

In this study, individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway, was estimated. The juveniles were incubated until hatching at two temperatures (±S.D. ), either 4.4 ± 1.5°C or 7.1 ± 0.6°C. Growth rate was estimated for 22 days in August–September when the fish on average were c. 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18°C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, this appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence the later growth as reported earlier from the studies of Atlantic salmon Salmo salar.     

Growth rate of tank-reared Mediterranean amberjack, Seriola dumerili (Risso 1810) fed on three different diets

Mediterranean amberjack Seriola dumerili (Risso 1810) has aquaculture potential. The growth rate and food conversion ratio of S. dumerili on three different types of food (A: 100% frozen sardines; B: 50% frozen sardines and 50% pellet; C: 100% pellet) were measured, and analysed with respect to temperature, condition index and chemical composition of the fish fillet. Wild S. dumerili, average body weight 248 g and average total length 26.9 cm were caught in August and September 1994 in the South Adriatic Sea near Dubrovnik, Croatia and kept in three tanks (n=15 in each tank; duration of experiment, 226 days). The fish that were fed on diet A [initial weight, 252 ± 71 g; total length (TL), 24.3 ± 2.6 cm] started feeding immediately; however, fish assigned to diet C began to feed entirely on the pelleted diet 1 month after the start of the experiment. The mortality of fish fed on diet A was negligible, the registered growth rate was 313 ± 74 g (124.2%), specific growth rate was 0.32% day^?1 and the food conversion rate was 6.7. The fish fed on diet B (initial weight, 246 ± 74 g; TL, 28.2 ± 2.5 cm) started to feed on day 3 and achieved a total growth rate of about 98% (final weight gain, 241 ± 69 g) and specific growth rate of 0.24% day^?1 (feed conversion rate of 9.00 and mortality 13%). The fish fed on diet C (initial weight, 246 ± 74 g; TL, 28.2 ± 2.5 cm) started to feed on the pellets after 1 month and had a growth rate of 87% (weight gain 214 ± 85 g), a specific growth rate of 0.24% day^?1 and a food conversion rate of 10.6 with considerable mortality (27%). In all three diet groups the fish grew with considerable variation in food consumption and growth rate, depending on seasonal temperature variations of the ambient sea water supplied to the rearing tanks. Chemical analysis showed that the protein level (amount) in the fish meat exceeded 20% in all three fish fillet samples.     

Biomass plasticity of the leaves and inflorescences of Acaena magellanica (Lam.) Vahl (Rosaceae) on Subantarctic Iles Kerguelen

Summary The relative allocation of biomass within monospecific stands of Acaena magellanica that vary in level of wind and water stress differ greatly. Populations in January 1983 varied in leaf biomass from 192 to 2373 g wet wt m^-2 (1105 to 10023 kJ m^-2) Inflorescences were not produced at either of these extremes of leaf biomass. In two populations with intermediate levels of leaf biomass (597 and 640 g wet wt m^-2, 3185 and 2664 kJ m^-2), inflorescent biomass was 104 and 273 g wet wt m^-2 (385 and 1127 kJ m^-2). The relative allocation to sexual reproduction is thus not constant in A. magellanica. The levels of energy in the leaves and inflorescences did not differ greatly despite differences in proximate composition.     

Biochemical composition of a dominant detritivorous fish Prochilodus lineatus along pollution gradients in the Paraná-Río de la Plata Basin

The biochemical composition of muscle, liver and stomach contents of a detritivorous fish Prochilodus lineatus was analysed and compared to settling particles and sediments along pollution gradients over 1500 km of the Río de la Plata Basin to evaluate the effects of anthropogenic discharges in a detritus food chain. The stomach contents of P. lineatus collected in the polluted Metropolitan Buenos Aires coast were enriched in proteins, carbohydrates and lipids, similar to settling particulates collected in the sewer area, and two to five times higher than underlying sediments, supporting the interpretation that P. lineatus feeds on unconsolidated organic flocs freshly decanted from mixed industrial and sewage outfalls. Fish from Buenos Aires had consistently higher standard length (L_S) and mass (M_T) slopes (b = 3·5), condition indexes (K = 3·01 ± 0·47, mean ±s.d .) and muscle fat content (fat = 23·8 ± 13·8% wet mass, mean ±s.d .) relative to northern fish (b = 2·7, K = 2·22 ± 0·39, fat = 3·4 ± 3·2% wet mass, respectively), suggesting that sewage‐derived organic matter was an enriched diet, which allowed an enhanced body mass gain and fat accumulation compared to organic‐poor vegetal detritus in the north Paraná area. Buenos Aires fish also showed higher hepato‐somatic indices (mean ±s.d . I_H 1·41 ± 0·49 v. 0·70 ± 0·32, respectively), which correlated with their two to three orders of magnitude higher hydrocarbon and polychlorinated biphenyl (PCB) loads, suggesting an enhanced detoxifying metabolism. The northward migration of fatty P. lineatus was evidenced by the presence of clear outliers in the L_S and M_T relationship, K and fat content along the Paraná River.     

Serum Level of Zinc and Copper in Sudanese Women with Polycystic Ovarian Syndrome

The paper’s objective was to estimate weekly Hg intake from fish meals based on intervention research. Total Hg (THg) concentrations in blood and hair samples collected from men (n = 67) from an intervention study as well as muscular tissues of fresh and after heat-treating fish were determined using the thermal decomposition amalgamation atomic absorption spectrometry method (TDA-AAS) using direct mercury analyzer (DMA-80). The mean of the estimated weekly intake (EWI) was estimated at 0.62 μg/kg bw/week in the range 0.36–0.96 μg/kg body weight (bw) /week through the consumption of 4 edible marine fish species every day (for 10 days) by the participants from the intervention research in Lodz, Poland. The Hg intake in the volunteers in our intervention study accounted for 38.6% of the provisional tolerable weekly intake (PTWI) (1.6 μg/kg bw, weekly) value. The average Hg concentration in the analyzed fish ranged from 0.018 ± 0.006 mg/kg wet weight (Gadus chalcogrammus) to 0.105 ± 0.015 mg/kg wet weight (Macruronus magellanicus). The results for the average consumers were within PTWI of methylmercury (MeHg). Moreover, the average concentration of Hg in the selected fish after heat treatment did not exceed the maximum permitted concentrations for MeHg (MPCs = 0.5 mg/kg wet weight) in food set by the European Commission Regulation (EC/1881/2006). Hence, the risk of adverse effects of MeHg for the participants is substantially low.     

Mercury Levels in Barbadian Fisher Folk and Commonly Caught Fish Species

Ocean fish are an important staple food for many Caribbean persons. Some species, however, have high Hg concentration levels and represent a significant source of Hg exposure. This study assessed Hg concentrations in fish species commonly caught and consumed in Barbados as well as Hg exposure of those who work in the fishing industry. Total Hg concentrations were measured in 100 fish samples. Human Hg concentrations were determined from hair snippets taken from 46 fisher folk and fish consumption habits evaluated using interview-administered questionnaires. Mercury levels varied by fish species with predatory fish species having the highest concentrations. Low Hg concentrations were found in dolphinfish (Coryphaena hippurus) and flyingfish (Hirundichthys affinis). Reported fish consumption rates were high and varied significantly between men and women, 2675 ± 1600 and 1275 ± 600 (g/week), respectively (p = 0.01). The median hair Hg concentration was 3.1 ± 2.3 μg/g (range: 0.01–15.6 μg/g) and significantly associated with consumption of “high-risk” fish species (p = .02). These results show that it is possible to make informed choices concerning fish consumption habits in order to maximize benefits while minimizing the effect of Hg exposures, especially for sensitive groups such as pregnant women and infants.     

Reproduction efficiency of the Horse Leech,Haemopis sanguisuga (Linnaeus, 1758)

The aquaculture sector has recently focused on alternative food sources due to increased costs and limited resources. Live food sources, such as invertebrates, have important roles in digestion processes of fish. It was aimed to determine the reproduction efficiency of the horse leech, Haemopis sanguisuga, which is expected to be used as an alternative live nutritional source in aquaculture in this study. The study was conducted at ambient temperature in the laboratory conditions for three months. A total of 25 gravid leeches with an average body mass of 6.91 ± 2.20 g were used. The leeches lost up to 75% of their body mass and laid 4.30 ± 1.49 cocoons at 12.0 ± 8.2 days interval during cocoon laying period. Leeches stopped laying cocoon when the temperature fell to 16 °C. The average of offspring hatched from the cocoons was 6.45 ± 2.86. The length–body mass relationship of the offspring was exponential (W = 0.012L^2.809, R² = 0.898). The results from the current study indicate that the basic biological parameter affecting the reproduction efficiency of H. sanguisuga is the size of the broodstock leeches, and reproduction activity weakens the broodstocks.     

Partial compensatory growth in hybrid tilapia Oreochromis mossambicus × O. niloticus following food deprivation

The capacity of hybrid tilapia Oreochromis mossambicus × O. niloticus [23.2 ± 0.2 g (mean ± SE)] to show compensatory growth was assessed in an 8‐week experiment. Fish were deprived of feed for 1, 2 and 4 weeks, and then fed to satiation for 4 weeks; fish fed to satiation during the experiment served as control. Water temperature gradually declined from 28.1 to 25.5°C throughout the experiment. Specific growth rate (SGR) decreased with progressive food deprivation. At the end of deprivation, body weight was lower in the deprived fish than in the control. Fish deprived for 4 weeks exhibited lower contents of lipids and energy in whole body, and higher moisture content and ratio of protein to energy (P/E) than those of the control; they also consumed feed faster than the control when normal feeding was resumed. All deprived fish showed higher food intake (FI) than that of the control during re‐alimentation; however, enhanced SGR was only observed in the fish deprived for 4 weeks. There were no significant differences in digestibility of protein and energy, food efficiency (FE) or energy retention efficiency between the control and deprived fish. At the end of re‐alimentation, deprived fish failed to catch up in body weight with the control, while content of moisture, lipids and energy, and P/E in whole body of the deprived fish did not significantly differ from that of the control. The results of the experiment revealed that the hybrid tilapia reared in freshwater showed partial capacity for compensatory growth following food deprivation of 4 weeks, and that growth compensation was due mainly to increased FI, rather than to improved FE.     

Intra‐ and interspecific differences in nutrient recycling by European freshwater fish

1. We measured N and P excretion rates of 470 individuals belonging to 18 freshwater fish species widespread in Western Europe. We assessed the effect of body mass on excretion rates at both the intra‐ and interspecific levels. 2. The high variability in per capita N and P excretion rates was mainly determined by differences in body mass. The scaling coefficients of allometric relationships for both N and P excretion rates were significantly lower than 1 (mean ± SE, 0.95 ± 0.04 and 0.81 ± 0.05, respectively). 3. The slope of the allometric relationship between fish mass and nutrient excretion rate was significantly different among species. We did not detect any influence of phylogenetic conservatism on fish mass and on excretion rates. Further investigations are needed to understand the biological determinants of these differences. 4. This high intra‐ and interspecific variability in per capita excretion rates, coupled with differences in fish body mass, produce marked differences in biomass‐standardised excretion rates. These results thus indicate the necessity for further experimental and in situ investigations on the consequences of nutrient recycling by fish in freshwater ecosystems.     

Effect of diet switch timing and food source on survival and growth of lake sturgeon

Studies were conducted to determine the effects of diet switch timing and food source on hatchery survival and growth of lake sturgeon (Acipenser fulvescens) during a 7‐ and 6‐week period in 2004 and 2005, respectively. Diet transitions to bloodworm (Diptera: Chironomidae) and black fly (Diptera: Simuliidae) larvae were undertaken 1, 2, 3 or 4 weeks after an initial diet of brine shrimp (Artemia spp.) in 2004, and 2 or 4 weeks after initiation of feeding in 2005. In 2004, mean (±SE) final survival was significantly lower following early (week 1, 50.8 ± 8.3%) vs late (week 4, 83.3 ± 3.9%) diet switches, regardless of diet type; however, rearing lake sturgeon on black fly larvae led to significantly higher mean survival rates (78.7 ± 3.3%) in comparison to bloodworm diets (56.5 ± 6.5%). Fish reared in 2005 on black fly larvae showed no significant differences in mean (±SE) final survivals when switched early (week 2, 96.7 ± 1.0%) vs late (week 4, 97.6 ± 0.5%), but those groups transitioned to bloodworm did significantly worse following the early diet switch (week 2, 91.9 ± 1.7%; week 4, 99.0 ± 1.0%). Final mean (±SE) mass was significantly higher for lake sturgeon reared on black fly larvae (0.63 ± 0.02 g) vs bloodworm (0.53 ± 0.02 g) at the end of the 2004 study period, despite having received fewer daily feedings; however, this difference was not observed the following year (bloodworm, 1.48 ± 0.07 g; black fly larvae, 1.43 ± 0.07 g). While there was no significant difference in final mean mass (±SE) of fish among the various diet switch points in 2004 (week 1, 0.54 ± 0.05 g; week 2, 0.57 ± 0.03 g; week 3, 0.60 ± 0.01 g; week 4, 0.59 ± 0.03 g), there was a significant advantage to transitioning fish early in 2005, regardless of food type (week 2, 1.60 ± 0.03 g; week 4, 1.31 ± 0.02 g). Given our results from both years, we conclude that transitioning larval lake sturgeon to black fly larvae following 2 weeks on an initial diet of brine shrimp can maximize survival rates without sacrificing final sizes, while reducing effort and cost associated with culturing brine shrimp and feeding bloodworm.     

The fish diet of black-browed albatrossDiomedea melanophris and grey-headed albatrossD. Chrysostoma at South Georgia

 The fish component of the diet of black-browed and grey-headed albatrosses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish represented 30% and 72% by mass of the diet of black-browed albatrosses and 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the contribution (by numbers, size and mass) of fish species mainly by using otoliths (54 representing 9 taxa and 57 representing 17 taxa in black-browed and grey-headed albatross samples respectively). For black-browed albatrosses in 1986 the main fish prey was Patagonotothen guntheri (77% of otoliths, 51% of estimated fish biomass) and a single large specimen of Icichthys australis (40% estimated biomass), whereas in 1994 Pseudochaenichthys georgianus was the main fish prey (57% of estimated biomass) with Magnisudis prionosa (30%) and Champsocephalus gunnari (12%) also making substantial contributions. Grey-headed albatross samples from 1986 were dominated by southern lampreys (40% by number, 79% of estimated biomass), lanternfish (32% of numbers, 9% by mass) and Patagonotothen guntheri (11% by mass); in 1994 Champsocephalus gunnari (42% by numbers, 24% by mass), Magnisudis prionosa (13% by number, 36% by mass), Muraenolepis microps (90% by number), Pseudochaenichthys georgianus (15% by mass) and lanternfish (18% by number but only 1% by mass) were the main prey. The importance of Patagonotothen guntheri to both species in 1986 and its absence in 1994 probably reflect albatrosses obtaining it from the commercial fishery, which was active in 1986 but closed in 1994. Otherwise the fish diet of black-browed albatrosses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross diet comprises deeper water mesopelagic species, especially lanternfish, which reflect its affinity for the Antarctic Polar Frontal Zone and associated oceanic upwellings. Received: 28 June 1995 / Accepted: 8 October 1995     

Growth, sex differentiation and gonad and plasma levels of sex steroids in male‐ and female‐dominant populations of Dicentrarchus labrax obtained through repeated size grading

Starting from 66 days post hatching (dph), European sea bass Dicentrarchus labrax were graded successively to create a fast growing (L‐extreme) and a slow growing (S‐extreme) population. The L‐extreme population grew significantly larger (ANOVA, n = 89–101, P < 0·01) attaining twice the wet mass of the S‐extreme population at 300 dph (130·9 ± 1·8 v. 66·7 ± 0·9 g, mean ± s .e .). When the two populations were sexed, the L‐extreme consisted of 96·5% and the S‐extreme of 30·2% females, while the ungraded control had 59·2% females. Sex differentiation began first in females at a total length (L_T) of 97 ± 4 mm and wet mass of 9·4 ± 1·2 g (150 dph), and was completed when fish reached 166 ± 6 mm and 53·4 ± 6·4 g (250 dph) in both sexes. Precocious maturation in males was positively correlated to growth. Gonad oestradiol (E₂) was significantly higher in the female‐dominant population at the onset of ovarian differentiation (ANOVA, n = 10, P < 0·05) and in the plasma after the appearance of the first primary oocytes (P < 0·01). Gonad testosterone (T) increased in both populations after sex differentiation (ANOVA, n = 10, P < 0·05), while plasma levels were significantly higher in the male‐dominant population (P < 0·001). Both gonad and plasma 11‐keto testosterone (11‐KT) were significantly higher in the male‐dominant population (ANOVA, n = 10, P < 0·01) reaching maximal values at spermiation. The results suggest that E₂ is closely related with ovarian differentiation and the onset of oogenesis, while T and 11‐KT is more related to spermatogenesis and precocious maturation.     

Effects of two parasites, Schistocephalus solidus (Cestoda) and Bunodera spp. (Trematoda), on the escape fast-start performance of three-spined sticklebacks

The fast‐start performance of three‐spined sticklebacks Gasterosteus aculeatus infected with Schistocephalus solidus and Bunodera spp. was determined and two distinct fast‐start responses (A and B) were observed. ‘A’ starts were of higher flexibility than B and three‐way ANOVA showed significant effects of A and B starts (P < 0·05), time (P < 0·05) and per cent standard body length, L_S (P < 0·05) on the orientation angle (angle of an individual segment of the fish with respect to the direction of travel). Schistocephalus solidus infection reduced maximum velocity (P < 0·05) and maximum acceleration (P < 0·05) of infected fish. Uninfected fish and fish infected with S. solidus up to a parasite index (parasite mass divided by the sum of fish and parasite mass) of 0·1 executed both types. Infected fish exclusively executed B starts for parasite index between 0·1 and 0·2. This was not due to a reduction in body flexibility associated with mechanical obstruction caused by S. solidus as no significant difference in the ratios of body width (P > 0·05) or depth (P > 0·05) to L_S were found between uninfected and infected fish. At a parasite index >0·2, infected fish were unable to perform escape fast‐starts increasing the likelihood of predation by their definitive hosts such as loons or belted kingfishers. Three‐spined sticklebacks infected with S. solidus with a parasite index of c. 0·2–0·3, however, were compromised by a suite of behavioural (e.g. increased foraging activity and amount of food consumed, increased risk associated with feeding and increased response latency to predatory stimuli), physiological (e.g. increased rate of oxygen consumption, slower growth, delayed sexual maturation and breeding success) and biomechanical (e.g. decreased fast‐start performance) factors. Bunodera spp. did not affect the escape fast‐start performance of three‐spined sticklebacks and no significant difference for maximum velocity (P > 0·05) and maximum acceleration (P > 0·05) was found.     

Diet spectrum of great cormorants (<Emphasis Type="Italic">Phalacrocorax carbo sinensis</Emphasis> L.) at the Donji Miholjac carp fishponds in eastern Croatia

This paper reports the results of a diet analysis from the digestive tracts of 203 great cormorants shot at the Donji Miholjac fishponds in eastern Croatia, in the period 2000–2002. Eight fish species were determined. The dominant species was common carp (Cyprinus carpio) with a relative frequency of 73.4%, followed by grass carp (Ctenopharingodon idella) (11.6%), bighead carp (Aristichthys nobilis) (7.2%), pikeperch (Sander lucioperca) (2.0%), wels catfish (Silurus glanis) (1.7%), pike (Esox lucius) (1.5%), topmouth gudgeon (Pseudorasbora parva) (1.5%) and Prussian carp (Carassius auratus gibelio) (1.1%). The diet spectrum of the great cormorants from the Donji Miholjac fishponds was in accordance with the structure of the fish population in the fishponds. The average stomach weight per bird was 244 g. When birds shot with an empty stomach were excluded, the average stomach weight increased to 286 g. The length of consumed fish ranged from 40–335 mm, with 47% of the fish belonging to the length category 100–149 mm. The study revealed no significant relationship between the weight of the consumed fish and the body weight of male and female cormorants.     

Growth and mortality of zebra fish, Brachydanio rerio (Hamilton Buchanan), maintained at two temperatures and on two diets

One hundred zebra fish per tank were maintained for 112 days at 24°C or 28°C in glass aquaria and fed a diet of flaked food made without cellulose (13.45 kJ g^?1, metabolizable energy, Type A) or with cellulose (8.71 kJ g^?1, metabolizable energy, Type B). Each experimental condition was repeated in triplicate (12 tanks). The weight of food given daily to the fish was based on daily records of survivors (from which mortality rates were calculated) and wet wt of fish (measured every 14 days) in each tank. All fish were fed with the same weight of food per day and the quantity of energy in the food in excess of standard metabolism (as a proportion of SM) was approximately 0–5 for fish maintained at 28°C and fed food B, 1–0 for fish maintained at 24°C and fed food B, 1–5 for fish maintained at 28°C and fed food A, and 2.2 for fish maintained at 24°C and fed food A. Non-ionized ammonia, nitrite and nitrate nitrogen in the tanks did not reach toxic levels although there was an increase in total ammonium nitrogen in one tank and a subsequent heavy mortality. It was assumed that this was caused by the build up of pathogenic bacteria. Apart from this tank, mortality was highest in tanks at 28°C with fish fed food A and second highest in tanks at 24°C with fish fed on the same diet. Growth was measured in units of length, wet and dry weights, carbon and energy. There was a good correlation (P < 0.001) between carbon (mgC mg^?1) and calorific (J mg^?1) values and a conversion factor of 46.2 J (mgC)^?1 was derived. Fish maintained at 24°C and fed food A had the highest rates of growth both in weight and in energy value per unit weight. Fish fed the same diet but kept at 28°C had the lowest growth rates. Both these groups of fish had the highest coefficients of variation in wet weights which increased during the experiment, indicating an increase in interaction within the tanks. There was agreement between the energy value of fish sampled for growth and a condition factor based on the length-weight relationships of fish remaining in the tanks. A correlation (P < 0.05) was found between instantaneous mortality and growth rates for fish between tanks when those maintained at 28°C and fed on food A were ignored.