Otolith microstructure and daily age of Anguilla japonica, Temminck & Schlegel elvers from the estuaries of Taiwan with reference to unit stock and larval migration

To test the hypothesis that the Japanese eel, Anguillu japonica , elvers in the eastern and western coasts of Taiwan are recruited from two different spawning grounds and to increase the knowledge of the early life history of the eel, the otolith microstructure and daily age of elvers collected from five estuaries in the coast of Taiwan during December 1989 through February 1990 were examined by scanning electron microscopy. The total length of elvers at arrival in the estuaries was similar among estuaries, averaging c . 56.0 mm and showed a seasonal decrease. The maximum radius of the sagittal otolith of elvers ranged from 124.46 to 181.82μm with a mean of 143.15 ± 12.72 μm. The otolith from centre to edge included an organic-rich primordium (9.20 ± 2.02 μm in diameter), a diffusively calcified core (20.94 ± 1.99 μm), and the daily growth increments; these three layers were probably deposited during the embryonic, yolk sac and feeding period respectively. The growth rate of the otolith was higher at the beginning of early life (0.5−1.0 μm day ⁻¹), lowest at approximately 100-days old (<0.5 μm day⁻¹), and highest 1 month before arrival at the estuary (> 1.0 pm day⁻¹). The mean age for elvers arriving in the estuaries of the coasts of Taiwan was approximately 170.4 ± 21.02 days. Neither the growth pattern of the otolith nor the age of elvers arriving in the estuary were significantly different among estuaries, indicating that the elvers in both eastern and western Taiwan were probably recruited from the same spawning ground. The growth pattern of the otolith in relation to larval migration was analysed.     

Indirect food web interactions increase growth of an algivorous stream fish

1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions.     

Capacity for growth compensation in juvenile three-spined sticklebacks experiencing cycles of food deprivation

The capacity of three‐spined sticklebacks Gasterosteus aculeatus (initial mean mass 0.280 g) to compensate for recurrent periods of food deprivation of 2, 4 or 6 days followed by 2 days of ad libitum feeding on enchytraeid worms over 56 days was assessed by measuring appetite and growth. Control fish were fed daily. The total number of days on which fish were fed ranged from 14 (6‐day cycle) to 56 (controls). Deprived sticklebacks were hyperphagic on the first day of re‐feeding in a cycle and this hyperphagia increased with successive cycles. Mean daily consumption on first day of refeeding was: controls, 62.9 mg; 2 days, 108 mg; 4 days, 98.8 mg; 6 days, 101 mg. The hyperphagia did not increase as the preceding period of deprivation within a cycle increased. Hyperphagia was not maintained on the second day of re‐feeding. The 4 day and 6 day groups initially showed hypophagia on the second day of re‐feeding. Mean daily consumption on second day of re‐feeding was: controls, 62.6 mg; 2 days, 62.2 mg; 4 days, 54.2 mg; 6 days, 50.0 mg. Over the experiment, consumption on the second day of the 4 day and 6‐day groups increased towards the control level, suggesting a developing compensatory response. The highest mean daily consumption per days fed was shown by the 2 day group. The relationship between number of days fed and total food consumption and specific growth rate suggested that the 2 day group almost compensated for the periods of deprivation. Performance declined for the 4 day and 6 day groups, although even at the highest level of deprivation, a positive growth was achieved. Mean specific growth rate in mass (% per day) was: controls, 2.33; 2 days, 1.89; 4 days, 1.21; 6 days, 0.86. Initial mass and total food consumption accounted for most of the variance in specific growth rate. Other indices of performance including lipid concentration, dry matter concentration and the RNA:DNA ratio in white muscle were positively related to quantity of food consumed by each group. Growth efficiency of sticklebacks in terms of wet mass gained and wet mass consumed over the experimental period was 19.4% and did not differ among control and treatment groups. The growth rates of the sticklebacks experiencing cyclical deprivation were comparable to growth rates previously recorded for sticklebacks fed daily, but consuming similar mean daily rations.     

Influence of stocking density of European eel (Anguilla anguilla, L.) elvers on sex differentiation and zootechnical performances

Survival rate, sex ratio and zootechnical performances were evaluated on 168 kg of Anguilla anguilla elvers (0.45 g) weaned into three groups (A1, A2, A3) at initial densities of 800, 1600 and 3200 g m⁻³, respectively. In order not to modify the sex ratio, animals weaned at the different densities were maintained separately during the trials, and no size grading was performed at the fattening phase.
Final mean weight achieved by females belonging to the different groups showed no statistically significant differences; weight of males was higher (P < 0.05) in A1 than in A3 where a higher percentage of males was observed. Sex ratio of eels was different among the groups, with a higher percentage of males in A3 (96%) than in A2 (78%) or in A1 (69%). This finding testifies to a sex differentiation strongly affected by pre-fattening stocking density of elvers. Final load showed an increase in males corresponding to a significantly reduced biomass between A1 and A2 (10.97 and 10.24 kg m⁻³) and A3 (8.44 kg m⁻³). Final survival rate ranged from 87% (A1) to 90% (A3). As to food conversion, a better rate was found in A1 (1.9:1) compared to A2 (2.1:1) and A3 (2.3:1) eels.     

Behaviour and swimming performance of elvers of the American eel, Anguitta rostrata, in an experimental flume

Migrating elvers of the American eel, Anguilla rosirata , were examined in an experimental flume to determine the effect of water speed and presence of substrate on swimming performance. Use of the substrate as a resting area between movements increased with increasing water speed. The number of elvers moving in the boundary layer above the substrate was significantly greater than those moving in the water column. Swimming speed in the water column and along the substrate increased with water speed. Rate of progress over ground in the water column and boundary layer increased slightly with water speed initially, but subsequently declined in the boundary layer. Overall, swimming speed increased linearly with increasing water speed and net upstream progress remained constant with increasing water speed. Use of the boundary layer probably was restricted by the thickness of the layer as a function of water speed. The boundary layer should be used to maximize distance and minimize energy expense when migrating upstream. Elvers appear to use substrate to avoid free stream velocities and not as a medium for movement. Fifty per cent of all elvers tested in a chamber without substrate, which had no resting places, were unable to swim; thus migrations may be limited by the need to rest. The potential migration rate was estimated to approach 100m per day, based on movements in the substrate chamber.     

Nutritional condition of Anguilla anguilla starved at various salinities during the elver phase

The effects of food deprivation and environmental salinity (<1, 10 and 20) on survival, fish morphology, organization of the digestive system and body lipid reserves in European eel Anguilla anguilla during the transition from glass eel to elver, were evaluated. Fasted elvers kept in fresh water were able to withstand starvation for >60 days, while those in brackish environments (salinity 10 and 20) reached the level of irreversible starvation at 37 and 35 days, respectively. The high level of lipid reserves contained in liver inclusions and the abdominal cavity (perivisceral deposits) in elvers might explain their long resistance to starvation and differences in fasting tolerance under different salinities. Fasting resulted in a significant reduction of the elvers' condition factor and body depth. There were severe histopathological changes in the digestive system and musculature, such as the alteration of the liver organization, and hepatic glycogen and lipid content, shrinkage of enterocytes and reduction of their height, pancreas degeneration, autolysis of the oesophageal and intestinal mucosa and disarrangement of myofibrils and degeneration of trunk musculature. Degeneration of the oesophageal and intestinal mucosa as a consequence of fasting might have impaired digestive and osmoregulatory functions in feed‐deprived fish, directly affecting the tolerance to starvation and survival. Length of food deprivation was associated with a significant increase in mortality, coefficient of variation, cannibalism and point of no return at high salinities. Mortality was dependent on food deprivation and salinity concentrations. Environmental salinity directly influenced the ability of elvers to withstand starvation; once glass eels metamorphosed into elvers, they tolerated starvation better in fresh water than in brackish environments.     

Donor life stage influences juvenile American eel Anguilla rostrata attraction to conspecific chemical cues

The present study investigated the potential role of conspecific chemical cues in inland juvenile American eel Anguilla rostrata migrations by assessing glass eel and 1 year old elver affinities to elver washings, and elver affinity to adult yellow eel washings. In two‐choice maze assays, glass eels were attracted to elver washings, but elvers were neither attracted to nor repulsed by multiple concentrations of elver washings or to yellow eel washings. These results suggest that A. rostrata responses to chemical cues may be life‐stage dependent and that glass eels moving inland may use the odour of the previous year class as information to guide migration. The role of chemical cues and olfaction in eel migrations warrants further investigation as a potential restoration tool.     

卫星灵芝液体发酵富集硒锌的研究

研究不同浓度的硒、锌对卫星灵芝菌丝体生长的影响,初步探讨卫星灵芝菌丝体生物富集硒、锌的效应。采用平板培养法及液体发酵法研究锌、硒对卫星灵芝菌丝体生长的影响及富集效应。培养基中不同浓度的亚硒酸钠对菌丝体生长均具有不同程度的抑制作用,但灵芝菌丝体的富硒量随着硒浓度的增加而提高,当亚硒酸钠浓度为40 mg/L时,菌丝体中的生物量、富硒量及富硒转化率最高,分别为1.54%、2 131.55 mg/kg、32.91%;培养基中硫酸锌浓度低于150 mg/L的范围内对卫星灵芝菌丝体生长有明显的促进作用,硫酸锌浓度为60 mg/L时菌丝体中的锌含量和富锌转化率最高,分别为1 142.91 mg/kg、1.76%。培养基中同时添加40 mg/L的亚硒酸钠和60 mg/L硫酸锌,菌丝体生长量1.60%,富硒量301.85 mg/kg,富硒率4.84%;富锌量为540.41 mg/kg,富锌率为5.72%。     

水貂妊娠与泌乳期的能量代谢

孕貂摄入日粮比孕前高8.03%,即摄入总能量高11.70%。产后,母貂摄入日粮与总能量的变化,近似S型曲线。孕貂体重与妊娠时间呈正相关,与泌乳时间呈负相关。妊娠期,孕貂每天摄入总能量超过呼吸量与粪便排出量之总和,则体重增加。泌乳期,母貂每天摄入总能量少于呼吸量、粪便排出量及泌乳量之总和,故体重减轻。     

Swimming performance of European eel (Anguilla anguilla (L.)) elvers

To determine the relation between swimming endurance time and burst swimming speed, elvers of the European eel, Anguilla anguilla (L.), were made to swim at speeds from 3.6 to 7.2 L (body lengths) s⁻¹ in both fresh and sea water. Swimming endurance time of elvers averaging 7.2 cm total length decreased logarithmically with increased swimming speed from 3.0 min at 3.5 L s⁻¹ to 0.7 min at 5.0 L s⁻¹, and again logarithmically but with a lesser slope to 0.27 min at 7.5 L s⁻¹. No differences were found between fresh and sea water elvers. In still water, elvers could swim at high speeds for about 10–45m before exhaustion, depending upon speed. Elvers would be able to make virtually no progress against water currents >50 cm s⁻¹. Drift in coastal water currents and selective tidal transport probably involve swimming speeds below those tested in this study. Migration into freshwater streams undoubtedly involves avoidance of free stream speeds and a combination of burst and sustained swimming.     

Evidence of differences in growth and food intake regulation in different genetic strains of channel catfish

Norris and USDA-103 strains of channel catfish Ictalurus punctatus were compared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day⁻¹) regimes. At the start of the experiment Norris fish weighed 2·8 g, USDA-103 fish weighed 14·0 g. Therefore, a regression of the loge of specific growth rate against the log_e of mean body size with an empirically derived fixed slope of -0·37 was used to compare growth rates. Under both feeding regimes the USDA-103 strain had faster specific growth rates and more efficient food conversion. In subsequent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were acclimatized to tank conditions for 3 weeks prior to voluntary food intake measurement. Half of the groups were deprived of food for 2 days prior to food intake measurement, while the remaining groups were fed 1% body weight day⁻¹. The USDA-103 strain fish ate significantly more food and grew faster than the Norris strain fish. Previously fasted Norris fish subsequently ate more than their fed counterparts, whereas the fed USDA-103 fish consumed more food than the fasted USDA-103 group. When the USDA-103 strain fish were deprived of food for 4 , 2 or 0 days, all groups subsequently consumed between 4·5 and 5·0% of body weight in one meal. The USDA-103 fish, unlike the Norris fish were not stimulated to consume more after short-duration fasting. Taken together, these results suggest that there are genetic differences in growth, food conversion ratio and regulation of food intake between Norris and USDA-103 strains.     

Migratory patterns and contribution of stocking to the population of European eel in Lithuanian waters as indicated by otolith Sr:Ca ratios

Otolith Sr:Ca ratios were examined to evaluate the contribution of the stocked eel Anguilla anguilla elvers, which have been stocked in Lithuanian waters and mixed with naturally recruited eels for several decades, to the native eel population. Stocked eels were identified by the freshwater signature (Sr:Ca ratios <2·24 × 10⁻³) on the otolith after the glass eel stage. Naturally recruited eels, that had migrated through the North and Baltic Seas, were characterized by an extended seawater and brackish-water signature (Sr:Ca ratios >3·23 × 10⁻³) after the glass eel stage. Of 108 eels analysed, 21 eels had otolith Sr:Ca ratio profiles consistent with stocking while 87 showed patterns of natural recruitment. The ages of naturally recruited eels arriving in Lithuanian fresh waters varied from 1 to 10 years, with a mean ±  s.d . age of 5·2 ± 2·1 years. Eels from the inland Lake Baluošai were all freshwater residents of stocked origin. Stocked eels, however, accounted for only 20% of the eels from the Curonian Lagoon and 2% of eels sampled in Baltic coastal waters. This finding does not support the hypothesis that the eel fishery in the Curonian Lagoon depends mostly on stocking.     

Handling of coarse and fine particulate organic matter by the aquatic insects Paraleptophlebia gregalis and P. temporalis(Ephemeroptera: Leptophlebiidae)

SUMMARY 1. Paraleptophlehia gregalis and P. temporalis were abundant throughout a flow-controlled section of stream that contained large quantities of fine particulate organic matter (FPOM; 0.45 μm to 1 mm in diameter), and in upstream and downstream areas.
2. In laboratory studies, Paraleptophlebia spp. fed and grew on FPOM and CPOM (coarse particulate organic matter; greater than 1 mm in diameter); growth rate was not related to the particle size of food. In addition, these animals were able to survive and grow on various sizes of faecal material produced by shredders.
3. Paraleptopblehia spp. consumed relatively large amounts (0.16±0.09 mg per mg animal dry mass) of detrital material daily.
4. The mayflies had short gut content passage times (2–3 h) and low efficiencies of conversion of ingested food to body substance (0.08±0.07%). They egested relatively small, amorphous faeces,
5. The overall pattern exhibited by Paraleptophlebia spp. involved rapid processing and partial recycling, through relatively simple alimentary tracts, of large amounts of detrital material from a wide range of sources.     

Intensive culture of grass carp, Ctenopharyngodon idella, in circular tanks

Fingerling grass carp ( Ctenopharyngodon idella ) were cultured in 380 1 circular fiberglass tanks at stocking densities of 0.53, 1.06, 1.59 and 2.11 fish/1. Fish were fed duckweed ( Lemna minima ) to satiation. Fish grew from 2.7 g to a maximum mean weight of 72.7 g in 88 days. Fish stocked at 0.53 fish/1 grow more rapidly than those stocked at higher densities. Mean daily consumption rates were strongly correlated with oxygen levels and when oxygen levels dropped below 4 mg/1 consumption was reduced approximately 40%. High biomass, growth, and survival rates obtained during this study indicate grass carp are well suited for intensive tank culture.     

Production of metabolic and waste products by intensively farmed rainbow trout, Salmo gaivdnevi Richardson

The pollution production rate as measured by the increase in the amounts of ammonia, phosphate, nitrate, urea, and faeces in an intensive fish farm is described and is related to the amount of food fed per day or the biomass weight. Pollution production varied with fish size. Main pollutants produced per kg food fed per day were ammonia 31–37 g; phosphate 5.2–5.9 g; nitrate 9–15 g and suspended solids 40–9O g. Expressed as g kg⁻¹ fish produced per day ammonia ranged from 0.3–0.8 g; phosphate 0.067–0.17 g; nitrate 0.13–0.21 g and suspended solids 0.80–0.94 g. These rates differ from those reported in previous studies and these differences may be attributed to the design of the Shearwater farming system which involves self cleaning, intensively stocked tanks, a system which ultimately gives a more accurate assessment of pollution rates.     

Kill rates and food consumption of leopards in Bardia National Park, Nepal

This is the first study presenting data on kill rates and food consumption among Asian leopardsPanthera pardus Linnaeus, 1758. In Bardia National Park, Nepal, we found leopard kills by searching within areas with clusters of locations from radio collared leopards (2 males and 1 female with 2 cubs aged 4–9 months). We used two tracking schemes, 24-h intensive radio-tracking and daily monitoring, and we defined food consumption as the product of average prey live weight and proportion consumed. The three leopards consumed 89.2 kg of meat from five chitalAxis axis, one domestic dog and two birds during 19 days of 24-h intensive tracking, rendering an average (± SE) daily food intake of 4.7 ± 0.3 kgper capita. Twenty-five prey items (14 chital, one muntjacMuntiacus muntjak, four primates and six birds) were found during 180 days of daily monitoring of the female. All edible biomass was consumed in all kills, except for three chital, and the rate of kill consumption was positively related to the age of her cubs. The average daily food consumption of the female was 4.0 ± 0.3 kg/day, the kill rate (days/kill) including all prey categories was 5.6 ± 0.4 days, and the kill rate of ungulates was 10.6 ±0.7 days. Our food consumption estimates are higher than reported from arid African environments. We suggest that the high food consumption rate in our study is a consequence of a release from time-energy constraints due to high prey abundance.     

Effects of eflornithine hydrochloride (DFMO) on fetal development in rats and rabbits

Eflornithine hydrochloride (DFMO) is a highly selective, enzyme-activated, irreversible inhibitor of the enzyme L-ornithine decarboxylase (ODC). Because of its role in the biosynthetic pathway of polyamines, ODC is essential for the growth and development of newly implanted embryonic tissue. In order to assess its effect on embryonic growth and fetal development, at various stages of gestation, DFMO was administered in the drinking water to pregnant rats and rabbits at several concentrations (from 0.03% to 3.0%) and times (from days 7, 10, or 11 through days 18 or 19). Rats were killed on day 21 and rabbits on day 29 of pregnancy (day 1 = day of insemination), and the implantations and fetuses were examined. At a concentration of 1.0% (approximately 1,270 mg/kg/day) in rats and 3.0% (approximately 915 mg/kg/day) in rabbits, maternal food and water consumption and body weight gain were significantly reduced during the treatment period, and all implantations were aborted or resorbed. At lower doses (approximately 200-600 mg/kg/day) fetuses survived to term, though in reduced numbers, and a marked reduction in average fetal weight was seen. At levels of 60 mg/kg/day or lower, there were no deleterious effects to the dams or their offspring. Few malformations were detected at any dose level by gross teratologic examination; nor were any considered to have been drug induced because of their sporadic incidence. The embryotoxicity and severe growth retardation demonstrated by these studies verify that adequate polyamine levels are essential for normal embryonic and fetal development.     

Long-term tagging of elvers, Anguilla anguilla, with radioactive europium

Elvers were labelled with ¹⁵²Eu and ¹⁵⁵Eu. Optimum conditions turned out to be incubation for 3 h at 15°C in artificial sea water containing 2% NaCl and 0.1% KCl, EuCl₃ at 1 mCi (37 MBq) 1⁻¹ and an eel concentration of about 15%. Laboratory experiments pointed to a biological half-life of added europium of 1.6–0.5 years. Thirteen hundred ¹⁵⁵Eu-labelled elvers (50 Bq per eel), each weighing on average 0.21 g, were set out near Oskarshamn on the east coast of Sweden in June 1982. Three of these were caught nearby in May 1985 and one was caught in August 1985. They weighed then on average 56 g and showed no significant loss of label other than the physical half-life (5.1 years). All the radioactivity was found in bone tissue.     

Seasonal diet and prey selection of black‐backed jackals on a small‐livestock farm in South Africa

The extent to which black‐backed jackals (Canis mesomelas) selectively consume domestic sheep (Ovis aries) compared to wild prey is unknown. Using faecal analysis and prey surveys, we determined the seasonal diet and prey selection of jackals on a small‐livestock farm in South Africa. Sheep comprised 25–48% of the biomass consumed by jackals across seasons, and consumption peaked during the lambing seasons, indicating sheep often were the main food resource for jackals. Another main food resource was wild ungulates <50 kg, primarily springbok (Antidorcas marsupialis) and steenbok (Raphicerus campestris), which comprised 8–47% of the biomass consumed. Other important food items were mammals 1–3 kg (4–16%), which included hares (Lepus spp.) and springhares (Pedetes capensis), and small rodents (10–14%). Compared to the biomass available, jackals selectively consumed mammals 1–3 kg over sheep across all seasons, whereas wild ungulates <50 kg were selectively consumed over sheep in most seasons. Our results showed that jackals selectively consumed different food items throughout the year and that wild prey were consistently selected over sheep.     

Nutrition of Captive Cheetahs: Food Composition and Blood Parameters

Diet and nutrition of cheetahs was evaluated through survey, in conjunction with chemical analysis of feed and plasma samples, as part of a multidisciplinary effort to investigate underlying causes of low reproductive success in North American captive cheetah populations. Cheetahs consumed an average of 1.32 ± 0.4 kg of food daily, containing approximately 1,800 kcal, and maintained an average body mass of 36.7 ± 1.0 kg (n = 34). A commercially prepared horsemeat-based mixture comprised the dietary staple in 10 of 13 zoos responding to the survey, with additional whole or carcass portions offered 1--2 days per week to maintain variety and provide periodontal stimulation. Seven of 13 respondents fasted animals 1 day/week; five maintained no fast days. The primary meat product (n = 14 samples) contained: 58% crude protein, 28% crude fat, 7% total ash, 52 Iu/kg vitamin E, 9.7 Iu/g vitamin A, and 2,200 mg/kg taurine (dry basis). Mineral content of the same food item was: 1.9% Ca, 10.0 mg/kg Cu, 645.2 mg/kg Fe, 0.08% Mg, 22.6 mg/kg Mn, 1.3% P, 0.4% Na, and 127.8 mg/kg Zn. Nutrient levels, except vitamin E (and possibly Mg), met or exceeded recommendations established for domestic felids. Plasma α-tocopherol, retinol, and taurine (18.1, 1.82, 128.4 μmol/L, respectively) concentrations were similar to normals for domestic felids, as were mean plasma mineral levels (n = 81; in mEq/L: 5.64 (Ca), 0.03 (Cu), 0.03 (Fe), 2.0 (Mg), 166.0 (Na), 12.3 (P), and 0.026 (Zn)). No gross physiological or dietary nutrient imbalances were evident from this survey. © 1993 Wiley-Liss, Inc.