Recruitment of the amphidromous goby <Emphasis Type="Italic">Sicyopterus japonicus</Emphasis> to the estuary of the Ota River,Wakayama, Japan

Ecological aspects of recruitment in the amphidromous goby, Sicyopterus japonicus, were studied from larval collections made with a set net in the estuary of the Ota River, Wakayama, Japan. The abundance patterns of the 12,766 larvae collected from 18 April to 26 August 2006 showed several peaks during the recruitment season. Their body sizes at recruitment ranged from 23.5 to 30.0 mm standard length (mean ± SD, 26.3 ± 1.1 mm), 0.11 to 0.49 g body weight (0.22 ± 0.05 g), and 8 to 20 condition factor (11 ± 2). The standard length of the goby larvae tended to decrease with the season, while their body weight slightly increased and resulted in an increase in condition factor. The recruitment of larvae occurred mainly during the daytime. Otolith growth increment analysis of 30 larvae collected by a square lift net on 30 April 2005 revealed that the oceanic larval duration after downstream migration ranged from 173 to 253 days (208 ± 22) after hatching. A limited time of recruitment in early summer and a considerably long duration of oceanic life (about a half year) appeared to be unique characteristics of this Sicyopterus species that lives in a temperate region in comparison to other tropical species of the genus Sicyopterus that all have year-round recruitment.     

Starvation reduces the heat shock protein responses in white sturgeon larvae

This study investigates the responses of white sturgeon larvae (Acipenser transmontanus) to starvation and thermal stress, through the measurement of nutritional status (i.e. growth performances) and cellular biomarkers: heat shock proteins (Hsp) 70 and 90. White sturgeon larvae (25 day post hatch; initial weight 179.0 ± 5.1 mg) were fed (20% body weight per day) or starved for 24, 48 or 72 hrs. Every 24 hrs, five larvae from each of the starved or fed treatment replicates were exposed to heat shock resulting from an increase in water temperature from 19°C to 26°C, at a rate of 1°C per 15 min, and maintained at 26°C for 4 hrs. No mortality was observed in this study. Starvation significantly (p < 0.05) decreased the body weight and body contents of energy, protein, and lipid of the experimental larvae, compared to the fed larvae. Heat shock induced the expressions of Hsp70 and Hsp90 in both the fed and starved group; however, starvation reduced the induction at all sampling points. The current study demonstrates that poor larval nutritional status, assessed by the aforementioned parameters, reduced heat shock responses to thermal stress, as measured by heat shock protein levels. Furthermore, Hsp70 and 90 are more sensitive to heat shock and starvation, respectively. This may be, in part, a result of the different functioning of the heat shock proteins in cellular stress response and warrants further study.     

Post‐hatch dispersal of lake sturgeon (Acipenser fulvescens,Rafinesque, 1817) yolk‐sac larvae in relation to substrate in an artificial stream

Knowledge of the effects of environment and genotype on behavior during early ontogenetic stages of many fish species including lake sturgeon (Acipenser fulvescens) is generally lacking. Understanding these effects is particularly important at a time when human activities are fundamentally altering habitats and seasonal and diel physical and biotic stream features. Artificial stream channels were used in a controlled experiment to quantify lake sturgeon yolk‐sac larvae dispersal distance and stream substrate preference from different females (N = 2) whose eggs were incubated at different temperatures (10 and 18°C) that simulated stream conditions during early and late spawning and incubation periods in the Black River, Michigan. Data revealed that yolk‐sac larvae exhibited considerable variability in dispersal distance as a function of family (genotype), temperature experienced during previous (embryonic) ontogenetic stages, and environmental ‘grain’. Yolk‐sac larvae dispersal distance varied as a function of the juxtaposition of substrate to location of egg hatch. Lake sturgeon yolk‐sac larvae dispersed from mesh screens attached to bricks and settled exclusively in gravel substrate. Dispersal distance also varied as a function of family and egg incubation temperatures, reflecting differences in offspring body size and levels of endogenous yolk reserves (yolk sac area) at hatch. Expression of plasticity in dispersal behavior may be particularly important to individual survival and population levels of recruitment contingent upon the location, size, and degree of fragmentation of suitable (gravel) habitats between adult spawning and yolk‐sac larvae rearing areas.     

Physiological responses of the olive flounder, <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>, to a series stress during the transportation process

The main objective of this investigation was to examine physiological changes occurring within the olive flounder, Paralichthys olivaceus, in the presence of continuous stress factors. The experiment gave continuous stress, and each stress step is as follows: water level reduction (S1), selection process (S2), confinement (S3), air exposure (S4), transportation (S5), and storing in volume 0.5-t (S6) and 50.0-t (S7) rearing tanks for 24 h after transportation. The cortisol concentration showed a trend to continuously rise in response to consecutive stress from transportation from 7.4 ± 0.6 ng/ml in an experimental opening. The concentration showed the highest level, 25.3 ± 4.4 ng/ml, after confinement stress. Glucose concentration in S3 and S4 were increased significantly to 71.0 ± 13.0 and 78.7 ± 7.0 mg/dl, respectively (P < 0.05). Lactic acid was increased significantly from 0.5 ± 0.1 mM (S0) to 9.0 ± 1.2 mM (S4), but it did not recover until 24 h (7.0 ± 1.0 mM) after transportation (S6 and S7) (P < 0.05). Some contents displayed recovery within 24 h, but a longer time would be required for normal physical metabolism to resume after fish experienced stress. Therefore, it would be endangering the survival of this species if the transport were repeated within a 24-h period.     

Laboratory study of the susceptibility of hatchery reared Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) larvae to predation

The aim of the study was to determine the susceptibility to predation of Atlantic sturgeon larvae (Acipenser oxyrinchus) reared under traditional hatchery conditions. Experiments were conducted to determine whether predators would prey on Atlantic sturgeon if alternative prey was available and if the presence of substrate on the tank bottom impacted the number of Atlantic sturgeon consumed. European perch (Perca fluviatilis) was used as the predator, and the alternative prey were three‐spined stickleback (Gasterosteus aculeatus) or gudgeon (Gobio gobio). The predators and alternative prey were obtained from the wild. The mortality of sturgeon (n = 10) and alternative prey (n = 10) caused by four predators was recorded during 15 min trials. Trials with three‐spined stickleback and gudgeon as alternative prey were performed separately. Each experimental trial was repeated five times. The predators consumed significantly more Atlantic sturgeon than alternative prey in both the experimental setups when the bottom of the tank was covered with gravel and stone substrate and when there was no substrate. In trials with three‐spined stickleback the mortality of Atlantic sturgeon in both experimental setups was 94 ± 8.94%, while that of three‐spined stickleback in the setup with substrate was 20 ± 19.23%, and without substrate it was 22 ± 10.00%. European perch also consumed more Atlantic sturgeon than they did gudgeon, and the mean Atlantic sturgeon mortality in the experimental setup with substrate was 94 ± 5.48%, while for gudgeon it was 48 ± 8.37%. In the experimental setup without substrate the predators also consumed substantially more Atlantic sturgeon than gudgeon, with a mean Atlantic sturgeon mortality of 94 ± 8.94%, while for gudgeon it was 76 ± 5.48%. The study indicated that hatchery reared Atlantic sturgeon larvae are susceptible to predation by European perch. Predation could impact the survival of juvenile Atlantic sturgeon in the natural environment, and it could be one of the factors that is impeding the restoration of this species in the Baltic Sea basin.     

Molecular Studies on the Microbial Diversity Associated with Mining-Impacted Coeur d’Alene River Sediments

Mass mortalities of larval cultures of Chilean scallop Argopecten purpuratus have repeatedly occurred in northern Chile, characterized by larval agglutination and accumulation in the bottom of rearing tanks. The exopolysaccharide slime (EPS) producing CAM2 strain was isolated as the primary organism from moribund larvae in a pathogenic outbreak occurring in a commercial hatchery producing larvae of the Chilean scallop Argopecten purpuratus located in Bahía Inglesa, Chile. The CAM2 strain was characterized biochemically and was identified by polymerase chain reaction amplification of 16S rRNA as Halomonas sp. (Accession number DQ885389.1). Healthy 7-day-old scallop larvae cultures were experimentally infected for a 48-h period with an overnight culture of the CAM2 strain at a final concentration of ca. 10⁵ cells per milliliter, and the mortality and vital condition of larvae were determined by optical and scanning electron microscopy (SEM) to describe the chronology of the disease. Pathogenic action of the CAM2 strain was clearly evidenced by SEM analysis, showing a high ability to adhere and detach larvae velum cells by using its “slimy” EPS, producing agglutination, loss of motility, and a posterior sinking of scallop larvae. After 48 h, a dense bacterial slime on the shell surface was observed, producing high percentages of larval agglutination (63.28 ± 7.87%) and mortality (45.03 ± 4.32%) that were significantly (P < 0.05) higher than those of the unchallenged control cultures, which exhibited only 3.20 ± 1.40% dead larvae and no larval agglutination. Furthermore, the CAM2 strain exhibited a high ability to adhere to fiberglass pieces of tanks used for scallop larvae rearing (1.64 × 10⁵ cells adhered per square millimeters at 24 h postinoculation), making it very difficult to eradicate it from the culture systems. This is the first report of a pathogenic activity on scallop larvae of Halomonas species, and it prompts the necessity of an appraisal on biofilm-producing bacteria in Chilean scallop hatcheries.     

The effect of substrate rearing on growth,aerobic scope and physiology of larval white sturgeon Acipenser transmontanus

The effect of substratum on growth and metabolic rate was assessed in larval white sturgeon Acipenser transmontanus. Yolk‐sac larvae (YSL) were reared in bare tanks or tanks with gravel as substratum from hatch until approximately 16 days post hatch (dph). The effect of an artificial substratum was also evaluated on growth alone. Substratum had a significant effect on mass, with larvae reared in gravel and artificial substrata being larger than those reared without substratum. Routine metabolic rates were significantly lower and relative aerobic scope (the difference between maximum and routine metabolic rate) was significantly higher for YSL and feeding larvae (FL) reared in gravel relative to those reared in bare tanks, particularly before fish started feeding exogenously. Furthermore, gravel‐reared larvae had higher whole‐body glycogen concentrations relative to bare‐tank‐reared larvae. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) was relatively low in all treatments (< 1·7) indicating a limited ability to elevate metabolic rate above routine early in development and mass exponents for metabolic rate exceeded 1. Taken together, these data indicate that YSL reared without substratum may divert more of their energy to non‐growth related processes impairing growth. This finding underscores the importance of adequate rearing substratum for growth of A. transmontanus and may provide support for habitat restoration and alternative hatchery rearing methods associated with sturgeon conservation.     

Over-wintering physiology of age-0 lake sturgeon (<Emphasis Type="Italic">Acipenser fulvescens</Emphasis>) and its implications for conservation stocking programs

Lake sturgeon (Acipenser fulvescens) occupy some of the most northerly distributions of any sturgeon species and experience extended overwintering periods when resources may be limited. Conservation stocking is currently used as a management tool to enhance lake sturgeon populations that are at risk or endangered. One of the most limiting components of the conservation effort is our understanding of energy requirements that allow age-0 lake sturgeon to survive their first winter. In this study, age-0 fish (mean mass 5.6 g?±?0.5 S.E.; mean total length 12.7 cm?±?0.4 S.E.) were held in groups of 12 individuals (10 total groups) and starved for a period of four weeks while being held at 1?±?1 °C. This setting was intended to simulate winter conditions that occur in the Winnipeg River, MB, Canada. Post-winter fish condition and physiology were compared to pre-winter fish using survival, energy density, metabolic rate, glucose, triglyceride, protein, and cortisol production as metrics. While mortality was high (42%) during the experiment, results indicated that fish with total water content below 90% and energy density above 2000 J/g were more likely to survive. Whole body triglyceride, plasma triglyceride, plasma glucose levels, and standard metabolic rates were also found to significantly decline over time while whole body cortisol concentration increased. Understanding these thresholds will help in future refinements of rearing conditions, which look to improve the survival of age-0 lake sturgeon released into the wild pre-winter.     

Egg lipid and thiamine vary between early and late spawning lake sturgeon

Nutritional deficiency associated with reduced thiamine (vitamin B1) and reduced natural reproduction of salmonid species in the Great Lake Region is well established. The negative relationship between egg thiamine and lipid concentration to post-hatch larval growth and survival in teleost species, coupled with the limited research of egg thiamine in Acipenseriform species of conservation concern, including lake sturgeon, indicates that study of thiamine concentrations lake sturgeon eggs is warranted. Eggs were collected from females (N = 12) during the early and late portion of the spawning run in 2007 in a wild population from Black Lake, MI. Concentrations of thiamine, lipid and fatty acid concentration were measured along with female biological information (body size and egg size) and characteristics of larvae at hatch. Significant differences in egg thiamine concentrations were observed between early- and late-spawning females (mean ± SD: 2.36 nmol·g⁻¹ ± 1.09 vs. 0.73 ± 0.25 nmol·g⁻¹, W = 0.05, p < .01). No significant relationships were observed between female body size or egg size and egg lipid or thiamine concentration. Differences in lipid and thiamine concentrations were not predictive of larval body size or yolk sac volume at hatch. Total and phosphorylated thiamine were correlated with n-3 polyunsaturated fatty acids, suggesting that dietary items were likely partially responsible for provisioning of essential compounds. Given the negative effects of low egg thiamine concentration on larval survival in other fish species globally, results indicate that further research in areas of nutrient acquisition and thiamine effects on larval survival, natural recruitment, and hatchery feeding strategies is warranted for lake sturgeon.     

Behavioural response of Kootenai white sturgeon (Acipenser transmontanus,Richardson, 1836) early life stages to gravel,pebble, and rubble substrates: guidelines for rearing substrate size

Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programmes creating habitats for spawning and rearing of early life stages. To determine the effects of rock size on motile early life stages, experiments were conducted in artificial streams to observe the behaviour of free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus) relative to rock size. Most (≥90%) of the free embryos in replicate test streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks, with few moving downstream. There was no difference in downstream movement of free embryos among rock treatments, therefore all rock types provided cover habitat. Similarly, in rock mixture tests, with a variable percentage of pebble, small rubble, or large rubble in different tanks, even fewer free embryos moved downstream. With increasing age, larvae increasingly used the open bottom and velocity refuges downstream of or alongside rocks of any size while drift feeding. Downstream movement of larvae in both rock regime tests was affected by rock size, with significantly reduced movement relative to increasing abundance of large rock (rubble). However, in all rock mixtures, free embryos (and later, larvae when they stopped dispersing) preferred the smallest rock size available (pebble; P = 0.0001). This suggests a strong innate preference of both life stages for small substrate that is likely related to increased survival. A rock mixture of 10% gravel (16–32 mm diameter) and 30–40% pebble (diameter, 30–60 mm) should provide adequate rearing substrate for free embryos and early‐larvae. The remaining 50–60% should be mixed rubble and boulders for spawning and egg rearing.     

Rainbow Darter (Etheostoma caeruleum,Storer, 1845) predation on early ontogenetic stages of Lake Sturgeon (Acipenser fulvescens,Rafinesque, 1817)

Previous molecular diet analysis identified lake sturgeon (Acipenser fulvescens, Rafinesque, 1817) DNA in the gastrointestinal tracts of stream-resident rainbow darters (Etheostoma caeruleum, Storer, 1845) during the egg incubation, free embryo, and larval drift stages. The objectives of this experimental study were to: (a) quantify levels of predation by rainbow darters on lake sturgeon at the egg and free-embryo stages; and (b) evaluate whether predation varied as a function of substrate size and rainbow darter body size. We conducted experimental trials in 23-L polycarbonate tanks 0.41 m (L) × 0.33 m (W) × 0.30 m (D) with a standardized benthic area of 0.14 m². The tanks were randomly assigned one of two different substrate size classes: large rock (51.35 mm ± 0.91 mm) or small rock (27.68 mm ± 0.57 mm). We stocked individual rainbow darter, which were deprived of feed for 48 hr, with lake sturgeon (133 individuals/m²) in each of 12 replicates per ontogenetic stage and substrate type. The number of surviving lake sturgeon was quantified following a 24-hr predation exposure period. We used a generalized linear model with a binomial distribution to assess the influence of ontogenetic stage, substrate size, and rainbow darter body size on proportional lake sturgeon survival. Predation on lake sturgeon occurred at both egg (6.25 ± 1.16 individuals, mean ± 2SE) and free embryo (3.08 ± 1.08 individuals, mean ± 2SE) stages. Egg proportional survival was generally lower than at the free embryo stage in both substrate sizes; however, free embryo proportional survival was greater in small substrate trials. Rainbow darter total length did not affect the probability of lake sturgeon survival at either developmental stage. Results demonstrate that rainbow darters prey on early ontogenetic stages of lake sturgeon, corroborating previous results based on genetic diet analysis. Results fill a major knowledge gap concerning the vulnerability of pre-drift sturgeon to predation by an abundant river resident species that was previously discounted as a predator for early ontogenetic stages of lake sturgeon due to its small body size.     

Dynamics and extent of larval lake sturgeon Acipenser fulvescens drift in the Upper Black River, Michigan

Lake sturgeon larval drift is not uniform in time or space and subsequent efforts to determine the relative abundance have suffered because of the lack of information during this early life history period. The purpose of this study was to obtain information about the early life history of lake sturgeon, determine the extent and duration of lake sturgeon larval drift, and examine this relationship to water flow and temperature in the Upper Black River, Michigan. This study also compares the results of other studies to further evaluate the dispersion of larvae. Larval production was quantified using drift nets anchored to the stream bottom from May to June in 2000–2002. Larval drift nets captured 780 larvae in 2000; 2975 larvae in 2001; and 2041 larvae in 2002. For the 2000, 2001, and 2002 spawning season, we estimated that 7107 (95% CL: ± 1470), 17 409 (95% CL: ± 5163), and 15 820 (95% CL: ± 3168) larval lake sturgeon were produced in the Upper Black River (UBR), respectively. Catch per unit effort values of drifting larvae were greatest after peak water flows, with most larvae captured in the middle of the river channel. A mean daily water temperature above 16°C was an important environmental stimulus that influenced peak larval dispersion away from spawning sites. The results of this study suggested that natural reproduction was still occurring in the Black Lake system.     

Growth and morphological development of laboratory-reared larval and juvenile climbing perch <Emphasis Type="Italic">Anabas testudineus</Emphasis>

Morphological development, including fin and labyrinth organ, body proportions and pigmentation, in laboratory-reared larval and juvenile climbing perch Anabas testudineus was described and behavioral features under rearing condition were observed. Body lengths (BL) of larvae and juveniles were 1.9 ± 0.1 (mean ± SD) mm just after hatching (day-0), 8.7 ± 1.3 mm on day-19, reaching 18.4 ± 2.1 mm on day-35 after hatching. Aggregate fin ray numbers attained full complements in juveniles larger than 8.3 mm BL. Preflexion larvae started feeding on day-2 following formation of the upper and lower jaws, the yolk being completely absorbed by day-7 after hatching. Teeth appeared in flexion larvae larger than 5 mm BL on day-6, with cannibalism starting shortly after and continuing with further growth. Melanophores on the body increased with growth, a large dark spot developing on the lateral midline around caudal margin of the body in the postflexion and juvenile stages. The labyrinth organ differentiated in postflexion larvae larger than 7.2 mm BL on day-16, with air-breathing starting at the same time. Body proportions attained constant in postflexion larvae larger than 7.0 mm BL, and habitat of fish shifted from bottom to mid-layer. With the exception of fin ray numbers, the above morphological developments corresponded to behavioral shifts that occurred in the postflexion stage (ca. 7 mm BL), their subsequent continuity illustrating that the species possessed most juvenile-equivalent functions from ca. 7 mm BL.     

Morphology and development of <Emphasis Type="Italic">Pteromalus cerealellae</Emphasis> (Ashmead) (Hymenoptera: Pteromalidae) on <Emphasis Type="Italic">Callosobruchus maculatus</Emphasis> (F.) (Coleoptera: Chrysomelidae)

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is an ectoparasitoid of several stored-product insect pests. Very little information has been published on its biology and development in host larvae, which typically are concealed within seeds. We documented the development of P. cerealellae within fourth instar larvae of its concealed host, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) infesting cowpea seeds. The preimaginal life stages of the parasitoid were characterized for the first time using morphological structures revealed by microscopic techniques including scanning electron microscopy. Pteromalus cerealellae produces hymenopteriform eggs and larvae. Eggs hatch into 13-segmented first instar larvae with peripneustic condition of spiracles. The larvae have simple, tusk-like mandibles, whereas the mandibles of the pupae and the adults are of the conventional toothed types. Using statistical analyses of the sizes of the larval mandibles and head capsules in conjunction with reliable characters such as the number of exuviae on the body of parasitoid larvae, cuticular folding, and excretion of the meconium, we recorded four larval instars for P. cerealellae. The data showed significant positive correlations between larval mandible lengths and widths of larval head capsules, as well as between mandible lengths and larval instars, suggesting that mandible length is a good predictor of the number of instars in P. cerealellae. Developmental time from egg to adult emergence was ∼12 d for females and ∼11 days for males at 30 ± 1°C, 70 ± 5% r.h. and 12L:12D photoperiod.     

Experimental test of the effect of maternal hormones on larval quality of a coral reef fish

Maternal hormones can play an important role in the development of fish larvae. Levels of the stress hormone, cortisol, in females are elevated by social interactions and transferred directly to the yolk of eggs, where they may influence developmental rates. In some vertebrates, prenatal exposure to high levels of testosterone determine early growth rates, social status and reproductive success. The present study examined whether post-fertilization exposure of eggs of the tropical damselfish, Pomacentrus amboinensis (Pomacentridae), to natural levels of cortisol or testosterone directly affects larval morphology at hatching. Maternal and egg levels of cortisol and testosterone varied widely among clutches of eggs from local populations around Lizard Island on the Great Barrier Reef. The morphology of larvae produced by these local fish populations also varied widely and differed significantly among sites (e.g., standard length: 2.6–3.4 mm; yolk sac area: 0.01–0.13 × 10⁻² mm²). Laboratory experiments showed that elevated cortisol levels in the egg reduced larval length at hatching, while slight elevations in testosterone increased yolk sac size. The influence of testosterone, and to a smaller extent cortisol, on larval morphology differed among egg clutches. These differences were partly explained by differences in initial egg hormone levels. Morphological changes induced by experimental hormonal regimes encompassed the entire range of variability in body attributes found in field populations. It is unclear whether cortisol influences growth alone or development rate or both. Testosterone appears to influence yolk utilization rates, and has no significant effect on growth, in contrast to its role in later developmental stages. Maternally derived cortisol and testosterone are important in regulating growth, development, and nutritive reserves of the embryo and larvae of this fish species. Factors that influence the maternal levels of cortisol and testosterone may have a major impact on larval mortality schedules and, therefore, on which breeding individuals contribute to the next generation. Received: 19 August 1998 / Accepted: 16 November 1998     

Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO₂, PO₂, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO₂ < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute (≤ 2h) hypercapnia significantly increased arterial PCO₂ (8-fold increase), ventilation frequency (2-fold increase), plasma HCO₃ ⁻ (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO₂ (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min⁻¹) stabilized, HCO₃ ⁻ reached its apparent maximum (23.6 ± 0.0 mmol⁻¹), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO₂ (2.5 ± 0.14 Torr), HCO₃ ⁻ (7.4 ± 0.59 mmol · l⁻¹), ventilation frequency (71 ± 7 breaths · min⁻¹), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine “spike”, and increased plasma catecholamines, cortisol, and arterial PO₂. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O₂ affinity (Bohr effect), as determined by construction of in vitro blood O₂ equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon. Accepted: 17 August 1997     

Relative larval loss among females during dispersal of Lake Sturgeon (<Emphasis Type="Italic">Acipenser fulvescens</Emphasis>)

Mortality that occurs during larval dispersal as a consequence of environmental, maternal, and genetic effects and their interactions can affect annual recruitment in fish populations. We studied larval lake sturgeon (Acipenser fulvescens) drift for two consecutive nights to examine whether larvae from different females exposed to the same environmental conditions during dispersal differed in relative levels of mortality. We estimated proportional contributions of females to larval collections and relative larval loss among females as larvae dispersed downstream between two sampling sites based on genetically determined parentage. Larval collections were composed of unequal proportions of offspring from different females that spawned at upstream and downstream locations (~0.8 km apart). Hourly dispersal patterns of larvae produced from females spawning at both locations were similar, with the largest number of larvae observed during 22:00–23:00 h. Estimated relative larval loss did not differ significantly among females as larvae were sampled at two sites approximately 0.15 and 1.5 km from the last section downstream of spawning locations. High inter- and intra-female variation in larval contributions and relative larval loss between nights may be a common feature of lake sturgeon and other migratory fish species, and likely is a source of inter-annual and intra-annual variation in fish recruitment.     

Effects of warm acclimation on serum osmolality,cortisol and hematocrit levels in the Antarctic fish, <Emphasis Type="Italic">Trematomus bernacchii</Emphasis>

Antarctic fish, such as the Trematomus bernacchii, living at −1.9°C maintain a serum osmolality of around 600 mOsm kg⁻¹, nearly twice that of temperate fish. Upon warm acclimation, Antarctic fish significantly lower their serum osmolality. It has been suggested that this response to warm acclimation is due to stress. The purpose of this study was to determine, whether upon warm acclimation there was a change in the levels of the stress hormone cortisol and hematocrit associated with the decrease in serum osmolality. T. bernacchii were warm acclimated up to 4 weeks and serum osmolality, cortisol and hematocrit were measured. Upon warm acclimation to +1.6 and +3.8°C over the course of 4 weeks, T. bernacchii significantly lowered their serum osmolality (from 547 ± 4 mOsm kg⁻¹ to 494 ± 6 and 489 ± 4 mOsm kg⁻¹, respectively), yet did not alter their serum cortisol (29 ± 6 nl ml⁻¹) or hematocrit (22 ± 1%) levels. These results suggest that warm acclimation does not induce a stress response in T. bernacchii.     

Growth and morphological development of laboratory-reared larval and juvenile <Emphasis Type="Italic">Hemibagrus filamentus</Emphasis> (Siluriformes: Bagridae)

Morphological development in laboratory-reared larval and juvenile Hemibagrus filamentus, and behavioral features observed under rearing conditions are described. Body lengths (BL) of larvae and juveniles were 3.8 ± 0.2 (mean ± SD) mm just after hatching and 11.7 ± 1.6 mm on day 15, reaching 26.5 ± 5.4 mm on day 30 after hatching. Aggregate fin ray numbers (for caudal fin, except for procurrent rays) attained full complements in specimens larger than 12.9 mm BL. A maxillary barbel bud appeared on day 0, and all larvae initiated feeding on day 3 with the development of mandibular barbels and conical teeth. Pectoral fin buds and primordial nostrils were present on day 1. Notochord flexion began on day 3, and the yolk was completely absorbed by day 4. Melanophores were scarce at hatching, but increased with growth to cover almost the entire body except the ventral surface of the head and body. Body proportions became relatively constant in juveniles, excepting maxillary barbel length that continued to increase, reaching over 40% BL. Fish were negatively phototactic from day 1. Cannibalism was observed from day 6, continuing to the juvenile stage.