Nucleic acid contents and growth of first-feeding walleye pollock larvae in response to prey densities typical of sub-Arctic ecosystems

The growth, nucleic acid and protein contents of walleye pollock Theragra chalcogramma larvae reared at prey densities of 10, 30, 50, and 500 prey 1^-1 were measured for the first 9 days after the feeding initiation at 6° C. Incremental growth rates of larvae (mm day^-1) were low and variable for the first 7 days after feeding initiation. Growth rates and rates of RNA, DNA, and protein accumulation by larvae reared at 500 prey 1^-1 were positive while those of larvae reared at the lower prey levels did not differ significantly from zero. The RNA/DNA ratio was variable and exhibited no significant trend among food treatments. Estimates of instantaneous protein growth rates ranged from - 6·7 to 13·2% day^-1 at food densities of 10 and 500 prey 1^-1, respectively, and were moderately correlated with larval RNA/DNA ratios ( r = 0·628). The results suggest that in situ protein growth rates of first-feeding pollock larvae may be influenced by prey fields within the range of ambient food densities reported for sub-Arctic ecosystems.     

The effect of calcium concentration on the toxicity of copper, lead and zinc to yolk-sac fry of brown trout, Salmo trutta L., in soft, acid water

Yolk-sac fry of brown trout were exposed to three levels of single trace metals (Cu, 20,40,80 nmol 1^-1; Pb, 12·5,25,50 nmol 1^-1; Zn, 75,150,300 nmol 1^-1) typical of concentrations reported for acid soft waters, in flowing, artificial, soft water media maintained at pH 4·5 and [Ca] of 20 or 200 μmol 1^-1for 30 days.
Mortalities were high in fry subjected to all levels of the three trace metals at [Ca] 20 μmol 1^-1, with 80% of the total deaths occurring between days 11 and 15 of the experiment. 25% mortality occurred at low [Ca] and pH 4·5 in the absence of trace metals, with only one death recorded at [Ca] 200 μmol1^-1'(Cu, 80 nmol 1^-1). At high [Ca] all three levels of Cu and Pb impaired net Na and K uptake; Cu was the only metal to reduce the uptake of Ca. The Zn treatments had no significant effect on mineral uptake. Calcification of centra was reduced by all three Cu treatments at [Ca] 200 μmol 1^-1. The lowest Zn concentration (75 nmol 1^-1) was the only other treatment to impair skeletal development. In the absence of trace metals, low [Ca] significantly reduced Ca, Na and K uptake, skeletal calcification and dry mass at pH 4·5.
The deleterious effects of low Cu, Pb and Zn concentrations at low pH and low [Ca], and the ameliorative effect of higher ambient [Ca], are discussed in relation to fishery status in soft, acid waters.     

Drinking rate, uptake of bacteria and microalgae in turbot larvae

The drinking rate of turbot larvae increased from 14 to 120 nl larva^-1 h^-1 from day 2 to 11 after hatching, which gave a slightly increased specific drinking rate (calculated per biomass) from day 2 to 7 (0·8–1·9 nl μg carbon^-1 h^-1. The clearance rate of both algae and bacteria was 10–100 times higher than the drinking rate, which indicated that the larvae had an active uptake of both algae and bacteria. On day 2 and 4 after hatching highest clearance rate was observed for Tetraselmis sp. On day 6 about the same clearance rate was observed for bacteria, Isochrysis galbana and Tetraselmis sp. Until day 4 the turbot larvae had a higher ingestion rate of Tetraselmis sp. than of I. galbana , whereas on day 6 the rates were similar (28–41 ng carbon larvae^-1 h^-1). The assimilation efficiency was somewhat higher for I. galbana than for Tetraselmis sp., and on day 6 the assimilated algae constituted 1·5 and 0·9% of the larval biomass for I. galbana and Tetraselmis sp., respectively.     

Growth and physiological changes during metamorphosis of Senegal sole reared in the laboratory

The metamorphosis of Solea senegalensis was studied in larvae reared at 20° C and fed four different feeding regimes. A, Artemia (4 nauplii ml⁻¹); B, Artemia (2 nauplii ml⁻¹); C, mixed diet (2 nauplii ml⁻¹ and 3 mg ml⁻¹ microencapsulated diet); and D, microencapsulated diet (3·7 mg ml⁻¹). Rotifers were also supplied in all cases during the first days of feeding. These feeding regimes supported different growth rates during the pre-metamorphosis period (regime A, G=0·376 day⁻¹; regime B, G=0·253 day⁻¹; regime C, G=0·254 day⁻¹; regime D, G=0·162 day⁻¹). Larvae started metamorphosis 9 days after hatching (DAH) when fed the regime A, 13 DAH with regime B, 11 DAH with regime C and 15 DAH with regime D. A minimum 5·6–5·9 mm L_T was required under all feeding regimes to initiate the metamorphosis. Eye translocation was completed when the larvae reached 8·6–8·7 mm L_T (regimes A, B and C), but only 7·3 mm L_T with regime D. 4·4–6·2 days were required to complete eye migration under the regimes A, B and C, and 18·3 days under the regime D. This transformation is concomitant with changes in body reserves, and with the pattern of some digestive enzymes.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Morphological development and allometric growth patterns in the juvenile seahorse Hippocampus kuda Bleeker

The morphological development and allometric growth patterns in the juvenile spotted seahorse Hippocampus kuda were studied under hatchery rearing conditions. Newborn spotted seahorses [mean ± s.d . standard length ( L _S) 9·33 ± 0·79 mm] were raised till the age of 124 days (119·35 ± 6·04 mm). Growth was characterized by three stages with two inflexion points occurring at day 21 and 76. The mean growth rates in the first, second and third stages were 0·68, 1·16 and 0·71 mm day⁻¹, respectively. The growth rate was most rapid in the second stage and was probably influenced by a behavioural shift from pelagic to benthic form. The mass ( M ) and L _S relationship was exponential ( M = 7·14 × 10⁻⁶ L _S^2·76), but the slope, b = 2·76, reflected negative allometric growth. Sexes could be distinguished at c. 110 days, and the sex ratio was unbiased. The L _S in males and females did not differ significantly. Morphological stageing series is proposed, which divides H. kuda juvenile development into eight stages based on the development of coronet, cheek and eye spines, keel and pigmentation. The morphometric ratios for all the body parts, except trunk length, showed considerable changes at a transition point occurring at c. 25 mm L _S. The high proportional growth in head length, head depth, pectoral fin base length, dorsal fin base length, snout length, snout depth and eye diameter at the initial stages, and the abrupt increase in tail length only after the first 2 weeks, possibly reflect development priorities during early development where important organs are being developed first for the enhancement of juvenile survival.     

Toxicity versus avoidance response of golden shiner, Notemigonus crysoleucas, to five metals

Avoidance thresholds and 96-h LC50 values were determined for golden shiners, Noiemigonus crysoleucas , for five individual elements: chromium, Cr; copper, Cu; cadmium, Cd; arsenic, As; selenium, Se. The avoidance concentrations were 73, 26 and 28 μgl^-1 for Cr-VI, Cu and As-III, respectively. Cadmium and Se were not avoided at experimental concentrations up to 68 and 3489 μg1^-1, respectively. Acute flow-through 96-h LC50 values were Cr-VI 55·0, Cu 84·6, and As-III 12·5 mg 1^-1, which were more than two orders of magnitude above avoidance concentrations. The acute flow-through 96-h LC50 values for Cd and Se were 2·8 and 11·2 mg 1^-1, respectively. These concentrations are 31 and 2·2 times the highest concentration employed in the avoidance tests, neither of which were avoided by the test organisms. Thus, simple toxicity tests do not identify the environmental hazard of some elements, and the most toxic elements may not elicit a behavioural response. When used in concert with tests of organism function, more realistic indicators of environmental hazard or safety may be determined.     

Seasonal variability in growth of larval Japanese anchovy Engraulis japonicus driven by fluctuations in sea temperature in the Kii Channel, Japan

Seasonal variability in the growth of larval Japanese anchovy Engraulis japonicus was examined through otolith microstructure analysis based on the samples collected from the northern side (inner area, IA) and the southern side (outer area, OA) of the Kii Channel from April 2006 to March 2007. Growth trajectories (otolith backcalculated mean standard length of 5 day intervals from 5 days after hatch to 24 days) as well as the most recent 5 day mean growth rate of larvae before capture ( G ₅) differed among months. Growth trajectories showed the same pattern as G ₅. In IA, mean ± s.d. G ₅ ranged from 0·31 ± 0·04 mm day⁻¹ (January) to 0·73 ± 0·06 mm day⁻¹ (October). In OA, mean ± s.d. G ₅ ranged from 0·36 ± 0·05 mm day⁻¹ (January) to 0·79 ± 0·11 mm day⁻¹ (August). G ₅ values declined from November to January and then started to increase. In general, the seasonal patterns of growth were similar between IA and OA, and a clear seasonal pattern in growth was identified. When the relationships among larval growth rate, sea temperature, zooplankton density and larval density were examined, growth rate was positively related with sea temperature in both areas and not related with the other factors. The similar pattern in growth observed between IA and OA was probably due to the low spatial variability in sea temperature compared to its seasonal variability.     

Ceratium in Lake Erken: vertical distribution, migration and form variation

External morphological features and growth characteristics of the dinoflagellates Ceratium hirundinella and C. furcoides were investigated in relation to the environmental conditions in Lake Erken. Three distinct population maxima were distinguished, one in June, one in July, and one in September. C. hirundinella dominated the spring and summer populations. C. furcoides was rare in June, but it continuously increased and composed ca. 18% of the Ceratium-cetts in the autumn. The size of a C. hirundinella decreased during the investigation period and a form with a long horn disappeared in June. Ceratium was most numerous during the warmer periods in summer when a distinct thermocline appeared and before the turnover period in September. The alga preferred depths down to 3 m where the blue light dominated and the following parametric magnitudes could be measured: oxygen contents >5 mg 1^-1, pH >7, HCO₃, >1.7 meq. · 1^-1, and a specific conductivity of ca. 250 mS · cm^-1. The algal growth periods displayed doubling times of 2.63 and 4.04 days at surface temperatures of 19°C and 15°C, respectively. The water transparency decreased 3.8 m when Ceratium reached cell densities of 13 individuals · ml^-1 (0–10 m depth). Its vertical migration demonstrated a dial rhythm with accumulation of cells in the surface waters during the day. Complicated patterns of surface avoidance occurred in clear weather and under wind stress.     

Differences in temperature conditions and somatic growth rate of larval and early juvenile spring-spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith to fish size relationship

Larval and juvenile herring Clupea harengus collected in the Polish part of the Vistula Lagoon in May-July 1997 had hatched between 17 April and 9 June and originated from three cohorts. The spawning season began on 1 March at 3·8° C and was completed on 3 June at 12·7° C. Mortality among larvae was high in the first 2 weeks of April, probably associated with significant temperature decrease at the beginning of the spawning season. The growth of 10–48 mm L _S herring was linear, highest for larvae and juveniles from the first cohort (0·58 mm mm^-1 day^-1), slower for the second cohort (0·55 mm mm^-1 day^-1) and the slowest for the third cohort (0·45 mm mm day^-1). Temperature effects on the growth were inconclusive and potentially unfavourable feeding conditions in June might have been responsible for the relatively slow growth of third cohort larvae and juveniles.
Relationships between otolith size (perimeter, length, width, area, and weight) and fish size ( L _S) differed among the three cohorts, related mostly to the positive temperature effect on otolith growth, individuals growing in warmer water had larger otoliths. Although a negative growth rate effect was observed as well, it was less significant.     

Differences in growth rates among cohorts of Encrasicholina punctifer and Engraulis japonicus larvae in the coastal waters off Tanshui River Estuary, Taiwan, as indicated by otolith microstructure analysis

The hatching dates of Encrasicholina punctifer and Engraulis japonicus larvae collected in the coastal waters off Tanshui River Estuary during the fishing seasons of 1992 and 1993 indicated that these two anchovies had protracted spawning seasons, which resulted in multiple recruitment cohorts. Encrasicholina punctifer larvae recruited to the estuary from October to March, while the majority of E. japonicus larvae came in March-May and to a lesser extent in October and November. The E. punctifer larvae on arrival to the estuary were 17·4–35·6 mm in length, 167ndash;89 days old and had growth rates of 0·4–1·0 mm day⁻¹, E. japonicus larvae were 12·1–32·7 mm in length, 19–62 days old and had growth rates of 0·7–0·9 mm day⁻¹. Growth rates were significantly different among cohorts and positively correlated to water temperature.     

Effects of river red gum, Eucalyptus camaldulensis, litter on golden perch, Macquaria ambigua

Aquaria with added river red gum, Eucalyptus camaldulensis , litter became hypoxic, with decreased pH and contained up to 30 mg 1⁻¹ tannin and lignin. Survival of golden perch, Macquaria ambigua , larvae in aquaria treated with a simulated annual litter density of 450 g m⁻² for 72 h was 14·9% for 15-day-old larvae and 0% for 8-day-old larvae. A litter density of 1223 g m⁻² resulted in total mortality for both age groups of larvae. Aeration increased survival of larvae to a minimum of 68·8% in 1223 g m⁻² litter treatments compared to 89·8% in aerated controls and 86·8% in non-aerated controls. A kinetic behavioural assay was used to detect alarm responses in golden perch larvae and juveniles exposed to leachates from river red gum bark, leaves and wood. Eight-day-old larvae exposed to bark and wood leachates (0·001–10 g 1⁻¹) exhibited an initial period of hyperactivity, followed by a concentration-dependent decrease in spontaneous activity. Larvae exposed to leaf leachates displayed only a decrease in spontaneous activity. Four-month-old juveniles exposed to wood leachates were also initially hyperactive, then progressively developed mild hypoactivity at increasing leachate concentrations. Juveniles exposed to wood leachates at 20g 1⁻¹ for 30min suffered 97·5% mortality in 96 h. Wood leachates induced dose-dependent lamellar fusion, epithelial dissociation and necrosis in the gills. The presence of toxic leachates and low oxygen availability in flooded river red gum forests may make these habitats unsuitable as nursery areas for native fish.     

Early life characteristics of pike, Esox lucius, in rearing ponds: temporal survival pattern and ontogenetic diet shifts

Survival, biomass and diet of pike, Esox lucius , larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m⁻² in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mm t.l .) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mm t.l .). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha⁻¹) and 121 mm T.L. (181.8 kg ha⁻¹) and stabilized between 121 and 139 mm t.l . Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mm t.l .) and between 74 and 121 mm t.l . (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mm t.l . juveniles. Average-sized pike exhibited a sequence of size-dependent shifts from a diet composed primarily (in terms of weight) of micro-crustaceans (at 13 mm t.l .), to chironomid larvae (at 74 to 99 mm t.l .), and finally macrocrustaceans (at 121 to 139 mm t.l .). Cannibalism was detected first among the largest fish at the 74 mm t.l . stage. Between-year diet similarity at various developmental stages was consistently high. In 70 mm t.l . fish harvested from different ponds, we found significant among-pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquaculture practices.     

Fast locomotion of some African ungulates

Ten species of ungulate were filmed, galloping in their natural habitat. They ranged in size from Thomson's gazelle (about 20 kg) to giraffe (about 1000 kg). They were pursued to make them run as fast as possible. The films have been analysed to determine speed, stride frequency, stride and step lengths, and duty factors. The dependence of these quantities on body size is discussed.  

Summary:

Fast locomotion of zebra, giraffe, warthog and seven species of Bovidae has been studied. The animals were filmed from a pursuing vehicle while galloping in their natural habitat.
Stride frequency was more closely correlated with limb length (represented by hip height) than with body mass. Mean stride frequency was proportional to (hip height)^-0·51 and maximum stride frequency to (hip height) ^-0·63.
Maximum speed was between 10 and 14 m s ^-1 for all species except buffalo (7 m s ^-1). It was not significantly correlated with body mass.
Since the small species ran at least as fast as the large ones they attained higher Froude numbers. Relative stride length was approximately 1·8 (Froude number)^0·39 for all species, irrespective of size. Relative step length was approximately 0·65 (Froude number)^0·2, both for the fore feet and for the hind ones. The vertical forces exerted by the feet are proportional to (body weight)×(Froude number)^0·2 so the forces at maximum speed are larger multiples of body weight for small species than for large ones.     

Bacteriological study of shrimp, Penaeus monodon Fabricius, hatcheries in India

Shrimp hatcheries often face problems of mortality caused by diseases. To understand the bacteriological status of shrimp, Penaeus monodon Fabricius, hatcheries in India, a study of hatchery water at different points was conducted in several hatcheries located along the east and west coast of India. The species composition of the bacterial flora was also determined. The total plate counts of raw sea water on tryptic soya agar ranged from 10² to 10⁴ ml^–1, whereas it ranged from 10⁴ to 10⁶ ml^–1 in larval tanks. In the larval tanks, the proportion of Vibrio species ranged from 50% to 73%, as compared to 31% in raw sea water. A mixed bacterial flora was observed in hatchery water; however, in the larval tanks, the flora in the larvae was predominantly made up of Vibrio species. A few of the tested Vibrio isolates were non-virulent to shrimp larvae under experimental conditions. Over 90% of the strains were resistant to amoxycillin, ampicillin, cephalexin, cephazolin, cloxacillin and sulphafurazole. Most strains showed sensitivity to tetracycline, chloramphenicol, and quinolones such as norfloxacin and ciprofloxacin.     

Resistance of a cased caddis larva to accidental entry into the drift: the contribution of active and passive elements

SUMMARY. . 1. The resistance to passive entry into the drift of first to fifth instar larvae of Allogamus auricollis (Pictet, 1834), a case-bearing caddis-fly, was investigated in the laboratory using an artifical stream channel.
2. Dead larvae in their cases were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to wash larvae away ranged from 3 cm s^-l (first instars) to 21 cm s^-1 for fifth instars. When the larvae were at right angles to the current (lateral position), these speeds were 2 and 9cm s^-1, respectively. In terms of force (Newtons), this passive resistance to drift ranged from 0.3x10^-6 N (first instar, frontal position) to 307.0x10^-6 N (fifth instar, frontal position). The data obtained in the experiments were in good agreement with values calculated from hydrodynamic equations, using biometric parameters of the larvae.
3. Total resistance to drift was studied by exposing living larvae to different current speeds. The speed just sufficient to wash larvae away ranged from 13 cm s^-1 in the first instar to 27.9 cm s^-1 in the fifth instar (frontal position). In terms of force, the total resistance to drift varied between 5.3x10^-6 N (first instar) and 547.5x10^-6 N (last instar).
4. The difference between total and passive resistance to drift was defined as'active resistance to drift', and is due to the effectiveness of a larva's attachment to the substrate. It ranged from 3.5x10^-6 N (first instar) to 222.8X 10^-6 N (last instar).     

Pathogenicity of live bacteria and extracellular products of motile Aeromonas isolated from eels

The pathogenic activities in vitro and in vivo of live bacteria and extracellular products (ECP) of 24 motile Aeromonas strains were investigated. Most Aer. hydrophila and Aer. jandaei isolates were pathogenic for eels (LD₅₀ 10^5·4-10^7·6 cfu fish^-1) but no Aer. sobria , Aer. caviae and Aer. allosaccharophila caused mortality in eels at doses of > 10^8·4 cfu fish^-1. Of these Aeromonas strains, Aer. hydrophila and Aer. jandaei in particular produced elastases and haemolysins against fish erythrocytes. ECP from Aer. hydrophila and Aer. jandaei caused degenerative changes in fish cell lines and were strongly toxic for eels (LD⁵⁰ 1·0–3·2 μg (g fish)^-1) reproducing the symptoms associated with natural disease. ECP from non-pathogenic species were inactive on fish cell lines as well as being poorly lethal for eels (LD⁵⁰ > 9·2 μg (g fish)^-1). All these biological activities of Aeromonas ECP were lost after heat treatment. These findings indicate differences between pathogenic and non-pathogenic Aeromonas species with respect to the expression of virulence factors, and show that elastases, haemolysins and exotoxins play a leading role in the pathogenicity of motile Aeromonas for eels.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.