Factors affecting mark quality of alizarin complexone-stained otoliths in juvenile black bream Acanthopagrus butcheri and a prescription for dosage

The relationships between otolith score, a function of increasing stain visibility, and the ratio of alizarin complexone (mg) to fish biomass (g) for 0·1, 0·6 and 7 g black bream Acanthopagrus butcheri show that acceptable marks are produced in all size classes using a stain-to-biomass ratio of 3·3 mg g⁻¹ following an immersion period of 24 h.     

Diet and body condition of cave‐dwelling dwarf crocodiles (Osteolaemus tetraspis,Cope 1861) in Gabon

We present the first ever observations of dwarf crocodiles (Osteolaemus tetraspis) selectively utilizing a cave ecosystem. We analysed crocodile diet to preliminarily assess the degree of ecological isolation of cave‐dwelling crocodiles from their forest‐dwelling conspecifics despite their physical proximity. We additionally conducted the first study of body condition of dwarf crocodiles and compared cave‐dwelling individuals to surface‐dwelling individuals from a variety of alternative habitats and sites as a means to better understand the implications of a semihypogean life on this species. Crocodiles captured in the caves appeared to forage exclusively in the caves and ate mostly cave crickets and bats, whereas crocodiles captured in the surrounding forest habitat consumed primarily freshwater crustaceans and insects and were not found to consume cave‐dwelling prey. Juvenile cave crocodiles had significantly higher body condition compared to juvenile forest crocodiles, which did not vary amongst forest locations. The difference in body condition between adult cave and forest crocodiles was not statistically significant despite also being higher; we suspect this is an artefact of the low sample size rather than a real nondifference. Forest adult crocodiles generally had significantly higher body condition than juveniles, but did not vary by site or habitat. This lack of variation suggests that habitat type is not the most important factor influencing dwarf crocodile body condition. Our results provide a unique insight into facultative cave use by a principally surface‐dwelling species and reinforce the necessity for further research into this unique system to better understand the evolutionary‐scale implications of cave habitat use by dwarf crocodiles.     

Hypoxia, low salinity and lowered temperature reduce embryo survival and hatch rates in black bream Acanthopagrus butcheri (Munro, 1949)

Embryo survival and hatch rates were measured in black bream Acanthopagrus butcheri exposed to different treatments of dissolved oxygen: hypoxic and normoxic, three salinities: 15, 23 and 35 and two temperatures: 16 and 20° C. Hypoxic conditions (50% saturation) reduced 1 day embryo survival by up to 15% ( P < 0·05) compared to embryos held in normoxic (>80% saturation) conditions. Temperature had no effect on the survival of embryos in these treatments, however, lowered salinity significantly reduced embryo survival at 20° C, but not at 16° C. Mean hatch rates were reduced by 10–28% in hypoxic treatments ( P < 0·05) and lowered salinity treatments ( P < 0·05). Hatching was delayed by up to 24 h at 16° C and very low (or zero) hatching occurred in hypoxic treatments at salinities of 15 and 23. These results confirm that environmental conditions in estuaries are important factors in determining spawning success of black bream and are discussed in relation to global warming and climate change that are likely to alter the physical conditions in southern Australian estuaries.     

Influence of freshwater flows on the distribution of eggs and larvae of black bream Acanthopagrus butcheri within a drought-affected estuary

This study tested the hypothesis that variable freshwater flow in the Gippsland Lakes, Australia, influences the location and extent of environmental conditions suitable for spawning and larval development of black bream, Acanthopagrus butcheri. Freshwater flow had a large influence on the salinity and level of stratification (difference between bottom and surface salinity) in the Gippsland Lakes. Freshwater flows throughout this study varied from no or low flows through to major flooding in 2007. Eggs of A. butcheri were found in similar concentrations throughout the lakes and rivers. More than 99% of larvae, however, were collected from within rivers, with very few larvae being collected from the lakes. A comparison of two spawning seasons revealed that the year with higher freshwater flows also had greater spawning activity and higher concentrations of larvae. Interestingly, there was a significant relationship between the distribution of eggs and larvae with the level of stratification. The highest concentrations of larvae occurred at sites with a difference in bottom and surface salinities of 15-20. This study demonstrates that despite A. butcheri spawning in the lakes and rivers, it is only locations with a halocline that function as larval nursery habitat.     

Comparison of growth and condition indices of juvenile flatfish in differentcoastal nursery grounds

Coastal and estuarine ecosystems in the eastern channel and southern bight of the North Sea provide nursery habitats for juvenile fishes. We examined the age 0-group juveniles of three flatfish speciesSolea solea, Limanda limanda and Pleuronectes platessa, collected in five nursery areas with different characteristics (three sites located near small estuaries and two affected by important inputs of industrial effluents), to evaluate habitat influence on their growth and condition. We measured a biochemical index (RNA:DNA ratio), a morphometric index (Fultons K condition index), plus a recent growth index (marginal otolith increment width) on each individual (about 3months old), collected during surveys in autumn 1999. The three indices displayed few significant differences among the five nursery sites and different patterns for each species. We suggest that the investigated nursery areas provide habitats of equivalent quality for the age 0-group juvenile flatfishes in spite of different anthropogenic disturbances. On the other hand, this study focuses on the importance of using different biological indicators to assess habitat quality and environmental stressors in coastal areas.     

Changes in RNA,DNA, protein contents and growth of turbot Scophthalmus maximus larvae and juveniles

The growth potential of turbot Scophthalmus maximus larvae and juveniles was studied using nucleic acid‐based indices and protein variables. The experiment was carried out from 4 to 60 days post hatching (dph). A significant increase in instantaneous growth rate during metamorphosis and retarded growth rate during post‐metamorphic phase were observed. Ontogenetic patterns of DNA, RNA and protein all showed developmental stage‐specific traits. The RNA:DNA ratio decreased up to 12 dph, then increased rapidly till 19 dph and fluctuated until 35 dph followed by a decline to the end. The RNA:DNA ratio was positively correlated with growth rate of juveniles during the post‐metamorphic phase, whereas this ratio was not a sensitive indicator of growth during the pre‐metamorphic phase and metamorphosis. The protein:DNA ratio showed a similar tendency to the RNA:DNA ratio. Changes of DNA content and protein:DNA ratio revealed that growth of S. maximus performed mainly by hyperplasia from 4 to 12 dph and hypertrophy until 21 dph during the pre‐metamorphic larval phase. Growth was dominantly hypertrophical from the early‐ to mid‐metamorphosing phase and hyperplastic thereafter. The results show that the DNA content and protein:DNA ratio can evaluate growth rates of larval and juvenile S. maximus on a cellular level.     

Delayed effects of larval predation risk and food quality on anuran juvenile performance

Metamorphosis can disrupt the correlation structure between juvenile and adult traits, thus allowing relatively independent evolution in contrasting environments. We used a multiple experimental approach to investigate how diet quality and larval predation risk affected the rates of growth and development in painted frogs (Discoglossus galganoi), and how these changes influence post-metamorphic performance. A high-energy diet entailed growth advantages only if predation risk did not constrain energy acquisition, whereas diet quality affected primarily the extension of the larval period. Predation risk influenced juvenile shape, most likely via the effects on growth and differentiation rates. Juvenile frogs emerging from predator environments had shorter legs and longer bodies than those from the nonpredator tanks. However, these morphological changes did not translate into differences in relative jumping performance. Neither size-adjusted lipid storage nor fluctuating asymmetry was significantly influenced by food quality or predation risk. Our data suggest that the post-metamorphic costs of predator avoidance during the larval phase are mostly a consequence of small size at metamorphosis.     

Responsiveness of selected condition measures of herring, Clupea harengus, larvae to starvation in relation to ontogeny and temperature

A laboratory experiment was performed to study the responsiveness of selected condition measures to starvation in herring, Clupea harengus, larvae in relation to temperature and ontogeny. The larvae at two intervals of development, i.e. stage 1 larvae with initial exogenous feeding and stage 2 larvae with established feeding prior to notochord flexion, were reared at three temperatures (5, 8 and 11°C) and subjected to sub-lethal durations of starvation. Temporal changes in standard length, dry weight, DNA concentration (% of dry weight), RNA concentration (% of dry weight), Fulton's condition factor (CF) and RNA/DNA were assessed and compared with fed controls. Starvation led to decreases in dry weight, CF, RNA concentration and RNA/DNA, while it led to an increase in DNA concentration. Higher responsiveness to starvation was observed at higher temperatures, and the magnitude of the changes was higher in stage 2 larvae. The shortest latency in starvation response was found with respect to RNA/DNA which was length independent in the size range studied. RNA/DNA was also significantly related to average DNA growth rate, and the model for DNA growth rate was, SGRDNA=4.49 RNA/DNA + 7.14 T – 0.42 T2 – 37.5 ; n=32, r2=0.85, p < 0.001). While the model seemed to adequately represent the average temperature dependent DNA growth, a relatively low classification success made it unsuitable for depicting individually starving larvae. Critical levels in DNA concentration can be used (2.2% for stage 1 larvae, 2.9% for stage 2 larvae) to differentiate starving larvae (after 3 – 5 days) from feeding larvae. RNA/DNA was the most sensitive and suitable condition index studied in detecting early starvation of herring larvae.     

Development and validation of methods for measuring multiple biochemical indices of condition in juvenile fishes

The investigation established and validated methods to measure multiple biochemical indices of condition (whole body total lipids, whole body triglycerides, muscle RNA : DNA ratio and muscle protein) simultaneously in the same individual juvenile fish. It also provided examples of their application using a species comparison (salmonids and cyprinids) of the degree of change in these indices after food deprivation. The results showed that juvenile rainbow trout Oncorhynchus mykiss were much more susceptible to a decline in all biochemical indices of condition than juvenile fathead minnows Pimephales promelas upon food deprivation. The combination of these techniques can be used to accurately assess condition and growth potential of individuals from wild fish populations.     

Effects of food type, feeding frequency, and temperature on juvenile survival and growth of Marisa cornuarietis (Mollusca: Gastropoda)

Abstract. The present experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the ramshorn snail, Marisa cornuarietis, in order to identify suitable husbandry conditions for maintaining multi‐generation populations in the laboratory for use in ecotoxicological testing. In this paper we focus on the effects of a combination of food types and feeding frequencies (i.e., the frequency with which the snails were offered food) on juvenile growth and survival at different temperatures. Offspring produced in the laboratory by wild specimens of M. cornuarietis, from Puerto Rico, were used to test the effects of three types of food (lettuce, alginate with fish food, alginate with snail mix) fed at three frequencies (given ad libitum on 4/4, 2/4, or 1/4 d) on juvenile survival and growth. The 4‐d feeding regimens were repeated four times, giving a total of 16 d for the experiments. The experiments were conducted at two temperatures (22° and 25°C) under a 12 h light:12 h dark photoperiod. Juvenile growth rates increased with increasing feeding frequency for all food types. The most rapid growth rates occurred in the high‐frequency lettuce treatments and the slowest growth rates in the low‐frequency lettuce and alginate with snail mix treatments. Juvenile snails grew faster at 25° than at 22°C, and mortality was about twice as high at the lower temperature. Growth rates were used to provide a rough estimate of time to maturity, which was determined to take about twice as long at 22° than at 25°C. The results showed that lettuce is the best food if supplied in abundance, but effects on growth are very dependent on feeding frequency and temperature. We conclude that 25°C is a more appropriate temperature for maintaining populations than 22°C, that lettuce provides a suitable food source, and that food should be supplied continuously for husbandry and toxicity testing of populations of M. cornuarietis.     

Patch selection by juvenile black surfperch (Embiotocidae) under variable risk: Interactive influence of food quality and structural complexity

The influence of risk on the selection of foraging patches by young-of-year black surfperch, Embiotoca jacksoni Agassiz, was investigated by laboratory and field experiments. These foragers harvest crustacean prey from a variety of benthic algal substrata. In field environments, patch types vary in two ways. First, substrata differ in structural complexity and probably afford different degrees of protection from predators. Second, substratum types vary in prey richness. There was no correlation between structural complexity and prey richness, and either or both factors could be a component of foraging patch value. Each patch is small and individual foragers are simultaneously confronted with arrays of patches encompassing the full range of variation in structure and prey richness. Furthermore, a major predator of young-of-year black surfperch, the kelp bass, Paralabrax clathratus (Girard), is patchily distributed in space and time. Thus similar arrays of patch types can be characterized by different levels of overall risk. Risk to foragers is dependent on light level as well as the presence and density of predators.The interplay between food quality and shelter potential in influencing patch choice was examined under different regimes of risk. Both laboratory and field experiments indicated patch preference was based primarily on food quality. However, the physical structure of a patch did become a component of patch choice as risk increased. The relative value of physical structure under high risk was dependent on the prey richness of a patch; food-poor substrata with high shelter potential remained unfavored even in situations of high risk.     

Interactive effects of elevated CO2 and temperature on water transport inponderosa pine

Many studies report that water flux through trees declines in response to elevated CO₂, but this response may be modified by exposure to increased temperatures. To determine whether elevated CO₂ and temperature interact to affect hydraulic conductivity, we grew ponderosa pine seedlings for 24 wk in growth chambers with one of four atmospheric CO₂ concentrations (350, 550, 750, and 1100 ppm) and either a low (15°C nights, 25°C days) or high (20°C nights, 30°C days) temperature treatment. Vapor pressure deficits were also higher in the elevated temperature treatment. Seedling biomass increased with CO₂ concentration but was not affected by temperature. Root : shoot ratio was unaffected by CO₂ and temperature. Leaf : sapwood area ratio (A_L/A_S) declined in response to elevated temperature but was not influenced by CO₂. Larger tracheid diameters at elevated temperature caused an increase in xylem-specific hydraulic conductivity (K_S). The increase in K_S and decrease in A_L/A_S led to higher leaf-specific hydraulic conductivity (K_L) at elevated temperature. Stomatal conductance (g_S) was correlated with K_L across all treatments. Neither K_S, K_L, nor g_S were affected by elevated CO₂ concentrations. High K_L in response to elevated temperature may support increased transpiration or reduce the incidence of xylem cavitation in ponderosa pine in future, warmer climates.     

The effects of prey species on food conversion efficiency and growth of an insectivorous lizard

Little is known about the effects of different prey species on lizard growth. We conducted a 6‐week study to determine the relative effects of prey species on growth parameters of hatchling western fence lizards, Sceloporus occidentalis. Lizards were fed house cricket nymphs, Acheta domesticus, or mealworm larvae, Tenebrio molitor. The effects of prey species on growth were determined by measuring prey consumption, gross conversion efficiency of food [gain in mass (g)/food consumed (g)], gain in mass, and gain in snout–vent length. Lizards grew well on both the prey species. However, lizards that fed on crickets consumed a significantly higher percentage of their body mass per day than those fed mealworms. Nevertheless, lizards that consumed mealworms ingested significantly more metabolizable energy, had significantly higher food conversion efficiencies, significantly higher daily gains in mass, and significantly greater total growth in mass than lizards that fed on crickets. Zoo Biol 27:181–187, 2008. © 2008 Wiley‐Liss, Inc.     

Interactive effects of light and nutrients on phytoplankton stoichiometry

The stoichiometric composition of autotrophs can vary greatly in response to variation in light and nutrient availability, and can mediate ecological processes such as C sequestration, growth of herbivores, and nutrient cycling. We investigated light and nutrient effects on phytoplankton stoichiometry, employing five experiments on intact phytoplankton assemblages from three lakes varying in productivity and species composition. Each experiment employed two nutrient and eight irradiance levels in a fully factorial design. Light and nutrients interactively affected phytoplankton stoichiometry. Thus, phytoplankton C:N, C:P, and N:P ratios increased with irradiance, and slopes of the stoichiometric ratio versus irradiance relationships were steeper with ambient nutrients than with nutrients added. Our results support the light–nutrient hypothesis, which predicts that phytoplankton C:nutrient ratios are functions of the ratio of available light and nutrients; however, we observed considerable variation among lakes in the expression of this relationship. Phytoplankton species diversity was positively correlated with the slopes of the C:N and C:P versus irradiance relationships, suggesting that diverse assemblages may exhibit greater flexibility in the response of phytoplankton nutrient stoichiometry to light and nutrients. The interactive nature of light and nutrient effects may render it difficult to generate predictive models of stoichiometric responses to these two factors. Our results point to the need for future studies that examine stoichiometric responses across a wide range of phytoplankton communities.     

Nutritional condition, starvation status and growth of early juvenile Japanese sea bass (Lateolabrax japonicus) related to prey distribution and feeding in the nursery ground

The nutritional condition and protein growth rates of Japanese temperate bass larvae and juveniles were studied in relation to prey distribution and feeding habits in the nursery grounds in Chikugo estuary, Ariake Sea, Japan. Samples were collected from a wide spatial area covering the nursery grounds of the fish in March and April 2003. Food habits of the fish were analyzed by examining the gut contents. Fish condition was evaluated by using RNA/DNA ratio and other nucleic acid-based indices and protein growth rates. The nucleic acid contents in individually frozen larvae and juveniles were quantified by fluorometric method. Two distinguished feeding patterns, determined by the distribution of prey copepods, were identified along the nursery ground. The first pattern showed the dependency of the fish on the calanoid copepod Sinocalanus sinensis, which was the single dominant prey in low saline upper river areas and the second pattern involved a multi-species dietary habit mainly dominated by Acartia omorii, Oithona davisae and Paracalanus parvus. Values of RNA, DNA, total protein, growth rates and for all the nucleic acid-based indices were higher in upstream areas than in the downstream areas. The proportion of the starving fish was higher in the downstream areas than in the upstream areas. Condition of juvenile sea bass was not equal throughout the nursery grounds; fish in the upper river were in better condition than those in the lower estuary. We speculated that utilization of S. sinensis, which appears a suitable prey item and provide a better foraging environment in the upstream nursery ground, is one of the key factors for early survival and growth of Japanese temperate bass larvae and juveniles in the Chikugo estuary.     

The effects of ration level on food retention time in juvenile lemon sharks,Negaprion brevirostris

Synopsis Fecal production was monitored to observe the effects of meal size on retention time of food in the digestive tracts of lemon sharks, Negaprion brevirostris. Initial appearance of feces occurred more rapidly when ration level was increased. The onset of fecal production was negatively correlated with rate of intake. Production of feces continued for a longer period of time when meal size was increased. Retention time of food was directly related to feeding rate, suggesting that the rate of digestion was constant. The correlation between retention time and intake on a percentage body weight basis was greater than the correlation between retention time and intake on an energy density basis. The use of agar to bind food may have delayed digestion and prolonged food passage for sharks fed an experimental diet.     

Effects of food deprivation on expression of growth hormone receptor and proximate composition in liver of black seabream Acanthopagrus schlegeli

The effects of food deprivation on the hepatic level growth hormone receptor (GHR) were investigated in black seabream (Acanthopagrus schlegeli) both at the protein level (by radioreceptor assay) and at the mRNA level (by ribonuclease protection assay). Serum levels of growth hormone (GH) and triiodothyronine (T₃) were also measured. Condition factor and hepatic proximate composition of the fish were also assessed. Significant decrease in hepatic GHR binding was recorded as early as on day 2 of starvation. On day 30 this decrease was even more pronounced, with the level in the starved fish reaching less than 20% the fed control level. A concomitant decrease in the hepatic GHR mRNA content was also noted during this period, with a progressive decrease from day 2 to day 30 of starvation. The extent of decrease in the mRNA content was less pronounced than the decrease in receptor binding, with the hepatic GHR mRNA content in the day 30 starved fish representing approximately 30% of the level in the fed control. In large contrast, serum GH level increased progressively during starvation. After 30 days of starvation, serum GH levels in the starved fish were more than three times the concentration found in the fed control. Serum T₃ levels, on the other hand, decreased during starvation, with the difference reaching significance on day 15 and day 30. After 30 days of starvation, serum T₃ levels in the starved fish were only approximately 40% the concentration found in the fed control. The hepatic lipid content exhibited an increasing trend during starvation. On day 30 the hepatic lipid content of the starved fish had doubled the level found in the fed control. However, the hepatic protein content did not exhibit much change during starvation. There was also a minor decrease in the moisture content of the liver during starvation, but the condition factor of the fish as a whole registered a gradual decrease during the course of food deprivation.     

Interactive effects of elevated summer temperature,nutrient availability,and irradiance on growth and chemical compositions of juvenile kelp,Eisenia bicyclis

Previous experiments with a factorial design have revealed the effects of several environmental factors on species performance and their interactions, which indicate synergistic or antagonistic effects. Temperature, nutrient availability, and irradiance are well‐known environmental factors that affect the growth and chemical composition of brown algae. However, relatively few studies have tested their combined effect on brown algal growth and chemical composition using a three‐way factorial design. We conducted a culture experiment to test the combined effects of elevated summer temperatures (23 and 26°C), irradiance (180 and 30 μmol photon m^?2 s^?1), and nutrient availability (enriched and non‐enriched seawater) on four relative growth rates (RGRs; based on wet weight, blade width, length, and area) and three chemical compositions (including carbon, nitrogen, and phlorotannin content) in juvenile sporophytes of the kelp Eisenia bicyclis. RGR based on blade width was the most sensitive to abiotic factors among all RGRs. A significant interaction between temperature and nutrient availability on this RGR suggested that the negative effect of elevated temperature was antagonized by a reduction in nutrient availability. Similarly, the positive effect of elevated irradiance on carbon content was synergized by reduced nutrient availability. Moreover, the negative effect of increased irradiance on nitrogen content was antagonized by elevated temperature in nutrient‐enriched treatments, but not in non‐enriched treatments. The content of carbon‐based phlorotannins increased with reduced nutrient availability but not with elevated irradiance. These results suggest that these abiotic factors have complex interactions on the growth and chemical composition of this species.     

Interactive effects of ontogeny, food ration and temperature on elemental incorporation in otoliths of a coral reef fish

The potential for environmental and physiological modification of elemental incorporation in otoliths is significant and must be validated before otoliths can be used reliably to estimate water parameters over the life history of a fish. We experimentally manipulated temperature and diet quantity for juvenile, sub-adult, and adult Acanthochromis polyacanthus, a tropical damselfish of the SW Pacific. Significant interactive effects between life history stage, temperature and food quantity were observed for otolith Ba/Ca, while significant interactions between stage and food were observed for Sr/Ca. Specific growth rates were negatively correlated with D_Ba and D_Sr for juveniles and sub-adults. These interactions indicated elemental incorporation dynamics varied depending on the life history stage, suggesting variation in effects of stage-specific metabolism or reproductive status. Our results highlight complex responses of elemental incorporation to both endogenous and exogenous factors. Interpretations of life history transects across otoliths must account for these effects to avoid confounding environmental variability with ontogenetic changes in physiology.