Larval Growth Rate Research Articles

Management of chicken manure using black soldier fly (Diptera: Stratiomyidae) larvae assisted by companion bacteria

Black soldier fly (BSF) is used for the management of organic waste, but research has hardly explored the effect of companion bacteria when chicken manure (CHM) is converted to insect biomass. In this study, we isolated nine bacterial species (FE01, FE02, FE03, FE04, FE05, FE06, FE07, FE08, FE09) from BSF eggs and one (BSF-CL) from the larval gut. These companion bacteria were inoculated into CHM along with BSF larvae (BSFL). Larval growth and manure conversion rates were determined. Results indicated that almost all bacteria individual bacteria in this study significantly promote BSFL growth. BSFL reared in manure with the species Kocuria marina (FE01), Lysinibacillus boronitolerans (FE04), Proteus mirabilis (FE08) and Bacillus subtilis (BSF-CL) had higher weight gain and manure reduction rates compared to the control. These four strains used were then examined as a poly-bacteria community experiment to determine BSFL growth and manure conversion. Manure inoculated with the poly-bacteria Group3 (FE01:FE04:FE08:BSF-CL = 4:1:1:1) and then fed to BSFL resulted in 28.6% more weight gain than the control. The greatest manure reduction rate (52.91%) was reached when companion bacteria were mixed at a ratio of 1:1:1:4. Additionally, the companion bacteria influenced the nutritional value of BSFL. Crude protein content in Group1 (FE01:FE04:FE08:BSF-CL = 1:1:1:1) was significantly larger than that of the control. Crude fat content in Group3 was significantly larger than that of the control. BSFL companion bacteria and their poly-bacteria compound improved manure conversion efficiency and nutrient accumulation in BSFL, reduced CHM quantity, increased larvae biomass, with potential economic gains in CHM management.

First Use of an Entire Age Cohort to Evaluate the Role of Sex in the Development of the Forensically Important Chrysomya megacephala (Diptera: Calliphoridae).

The age of a blow fly larval specimen found on a body can be used to estimate a minimum postmortem interval by comparing a physical feature of a larva (e.g., length) to a reference growth curve created under similar conditions. A better understanding of factors known to influence growth rates would lead to more precise estimates of larval age. A factor known to influence insect development, but almost always lacking in blow fly larval growth curves, is sex. We wanted to understand how sex might affect larval growth rates and therefore lead to more precise age estimates, in the forensically important blow fly Chrysomya megacephala (F.). We examined sex for an entire age cohort at 70 h and found on average, males were longer than females. To assess whether this difference would cause an investigator to interpret the results differently if comparing a larval specimen of one sex based on reference data from the other sex, we made sex-specific 95% prediction intervals. We did not find a difference when comparing a male specimen with the female prediction interval, but did find more females outside the interval than expected using the male interval. All females outside the male interval were shorter. Investigators commonly remove the largest individuals from a body to estimate age, so these females are less likely to be chosen. These results do not support the generation of sex-specific growth curves for this species, though this study's narrow scope means more information is required before making a final conclusion.

Combined effect of temperature, salinity, and rearing density on the larval growth of the black shell strain and wild population of the Pacific oyster Crassostrea gigas

Crassostrea gigas is a commercially important species which is the mostly widely cultured in the world. However, most of the oyster broodstock in China remains unselected. Through a 7-generation of selection on the shell color and growth traits of adult oysters, an excellent strain of C. gigas with black shell coloration and mantle has been developed. In order to facilitate the industrialized breeding, it is necessary to explore the growth performance of the black shell strain in larval stage and find out the optimal conditions for larval development. In this study, the accumulated growth rate and survival rate of the black shell strain and wild population of C. gigas larvae were measured respectively, and a central composite design as well as a response surface method was used to investigate the combined effect of temperature, salinity, and rearing density on the growth of both the two populations. No significant differences were found in survival rate between the two populations, and two model equations for the growth of the two populations were established. The optimizations of accumulated growth rate for two populations were explored. When the temperature, salinity, and rearing density was 25.14 °C, 30.28 psu, and 1.00 ind. ml−1, respectively, the accumulated growth rate for the black shell strain maximized 15.40 μm day−1. With a combination of temperature of 25.06 °C, salinity of 29.27 psu and rearing density of 1.00 ind. ml−1, the maximum value of accumulated growth rate for wild population was 13.20 μm day−1. Furthermore, the larval growth rates were compared between the black shell strain and wild population, and the larvae of the black shell strain significantly grew faster than those of wild population when temperature, salinity and rearing density in a suitable range.

The influence of larval growth rate on juvenile recruitment in Lake Erie walleye (Sander vitreus)

Growth-selective mortality as larvae can influence recruitment in marine fishes. Its importance in freshwater fishes, however, remains speculative. We quantified growth trajectories within annual cohorts (2011–2013) of Lake Erie walleye (Sander vitreus) and their relationship with recruitment. We hypothesized that selection against slow or fast growth would be associated with high mortality and poor recruitment, whereas weak or nonexistent growth-selective mortality co-occurring with fast growth would be associated with good recruitment. We used otoliths to reconstruct growth rates during the first 15 days of life from larvae collected during spring and juvenile recruits (survivors) collected during late summer. We documented growth-selective mortality during 2011 and 2013, which exhibited poor recruitment as expected. During 2012, growth selection was absent, but growth was slow when compared to historical averages, resulting in poor recruitment. Growth was also considered slow in 2011 and 2013, due to multiple interacting conditions. Our study indicates that the relationship among larval growth, mortality, and future recruitment is complex, highlighting the need for continued research into how larval processes affect recruitment dynamics in freshwater fishes.

Effects of hydroperiod on growth, development, survival and immune defences in a temperate amphibian

Abstract The many and varied effects of human‐induced environmental change have the potential to threaten animal biodiversity and species abundance. Importantly, human land use and global climate change are predicted to reduce water availability, which might have negative consequences for freshwater organisms. In this study, we tested for an effect of a shortened hydroperiod on larval growth and development, and post‐metamorphic survival and immune function in a temperate frog, Rana pipiens. Animals developing under pond drying conditions metamorphosed at a smaller size and had lower survival after metamorphosis. We found sex‐specific differences in larval period in our fastest drying treatment, with males metamorphosing more quickly than females. Individuals that developed under drying conditions also showed reduced skin swelling after phytohaemagglutinin injection, indicating a compromised immune response. We found support for trade‐offs between growth, development and post‐metamorphic immune function across hydroperiod treatments. Whole blood from animals with shorter larval periods had lower bacterial killing ability, and small‐bodied juveniles had lower antibody titres. Overall, our results indicate that a shortened hydroperiod can affect the rate of larval amphibian growth and development, and might negatively impact the condition of species that rely on freshwater for development. Our work improves understanding of the complex impacts that environmental stressors might have on the health of animal populations. A free Plain Language Summary can be found within the Supporting Information of this article.

Putting the pieces together: Recent growth, nutritional condition, and mortality of Engraulis anchoita larvae in the Southwest Atlantic

AbstractDynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.

Selection for improved white spot syndrome virus resistance increased larval survival and growth rate of Pacific Whiteleg shrimp, Liptopenaeus vannamei

Outbreaks of contagious diseases, including White spot syndrome virus (WSSV), occur more frequently due to environment changes and as commercial shrimp production becomes intensified. The over-arching aim of this study was to examine new traits to improve disease resistance of Whiteleg shrimp, Liptopenaeus vannamei, to WSSV. Specifically, we made a compressive evaluation of the breeding population to determine a suitable selection criterion for improved WSSV resistance. To achieve this objective, we analysed five traits (viral titre, WSSV resistance, larval survival, body weight and standard length) recorded for 120,000 individual shrimps that were offspring of 228 sires and 300 dams produced over two generations of selection in 2017 and 2018. Our restricted maximum likelihood mixed model analysis showed that there is additive genetic variation in viral copy number (or viral titre, viral load) with the heritability that equals 0.18 ± 0.02. Viral titre displayed a moderate and negative genetic correlation with WSSV resistance (rg = −0.55). These results suggest that viral titre can be used as a selection criterion to improve WSSV resistance, but selection for decreased viral titre (i.e., increased resistance) may not capture all genetic expression in WSSV resistance. In addition to the estimation of population genetic parameters, we evaluated direct response to selection for increased WSSV resistance, which was measured as differences in estimated breeding values between the high and low resistant lines. The direct genetic gain achieved for WSSV resistance averaged 12.9% after one generation of selection in this Whiteleg shrimp population. The selection program also resulted in positive impacts on growth and larval survival by 7% and 17%, respectively. There is abundant genetic variation in WSSV resistance (h2 = 0.19–0.27), suggesting that the tested Whiteleg shrimp population will continue to respond to future selection. Collectively, the results obtained in our study provide important information to assist the design and implementation of genetic improvement programs for disease traits in aquaculture species, including L. vannamei.

An optimal feeding strategy for black soldier fly larvae biomass production and faecal sludge reduction

The dual roles of efficient degradation and bioconversion of a wide range of organic wastes into valuable animal protein and organic fertiliser, has led to increased interest in black soldier fly (BSF) technology as a highly promising tool for sustainable waste management and alternative protein production. The current study investigated the potential application of BSF technology in the valorisation of faecal sludge (FS), a common organic waste in the urban informal settlements in low and middle-income countries. We evaluated the effect of different feeding rates (100, 150, 200 and 250 mg/larva/day), different feeding regimen and supplementation with other waste feedstock (food remains, FR; brewers waste, BW; and banana peelings, BP) on BSF larvae (BSFL) growth rates/yield and FS reduction efficiency. Results showed significantly (P<0.01) higher prepupal yield (179±3.3 and 190±1.2 g) and shorter larval development time (16.7 and 15 days) when reared on 200 and 250 mg/larva/day FS, respectively. However, different feeding regimes of FS did not significantly affect larval growth rate and prepupal yield (P=0.56). Supplementation of FS with other organic substrates resulted in significantly increased BSFL biomass production and substrate reduction, and shortened larval development time; with the effect was more pronounced when FS was supplemented with FR and at 30% supplementation. Protein:fat ratios for BSFL reared on FS, FS:FR, FS:BW were significantly (P<0.05) higher (2.51, 2.53, and 2.44, respectively) compared to FS:BP mixture (1.99). These results demonstrated that supplementation of FS with locally available organic waste can be used to improve its suitability as feedstock for BSF production and organic waste bioremediation from the environment. In conclusion, a daily feeding strategy of substrate containing FS supplemented with 30% organic waste co-substrate at feeding rate of 200 mg/larva/day can be used as a guideline for BSFL mass production and bioremediation of FS both at small- and large-scale level.

Optimized application of rotifers Brachionus plicatilis for rearing pikeperch Sander lucioperca L. larvae

This study aimed to optimize the use of euryhaline rotifer Brachionus plicatilis for rearing larval pikeperch Sander lucioperca L. We assessed motility of rotifers under salinities of 0‰, 2‰, 4‰, 8‰, and 16‰ over a 6-h period. Rotifers stocked into freshwater were completely immotile within 2 h. The motility of rotifers after 6 h was 10 ± 2.27% at 2‰, 35 ± 5.58% at 4‰, 79 ± 30.35% at 8‰, and 92 ± 1.98% at 16‰. A second trial quantified the effect of the target salinity levels on pikeperch gut fullness over the course of 11 h. The gut fullness of larvae fed with rotifers was significantly lower at 8‰ salinity than in other tested groups. Salinity of 16‰ resulted in 100% mortality. Survival and growth of pikeperch larvae from 4 to 11 days post-hatching (DPH) was analyzed at low (2‰ and 4‰) and medium (8‰) salinity. Differences in larval performance under tested salinities were found in survival (S), total length, SGR, eye diameter, myotome height, and gut fullness. The highest mean survival (S) and specific growth rate (SGR) were obtained at 2‰ (S = 64%; SGR = 10 ± 5.4% day−1) and 4‰ (S = 65%; SGR = 8.23 ± 3.4% day−1) salinity and significantly differed from 8‰ (S = 36%; SGR = 5 ± 2.3% day−1) and control (S = 34%; SGR = 7 ± 3% day−1) at 11 DPH. At the conclusion of the trial (11 DPH), larvae of all exposures and control presented normal histology with no signs of pathology. Morphometric analyses revealed significant differences in brush border and fold height of anterior intestine among treatment groups. Larvae at 2‰ salinity showed significantly higher intestinal fold height (31.2 ± 5.40 μm) compared to those at 4‰ (26.5 ± 6.11 μm), 8‰ (26.3 ± 4.52 μm), and control (22.8 ± 5.13 μm) (p ˂ 0.05). Larvae at 4‰ salinity had significantly higher brush border height (2.50 ± 0.73 μm) compared to those at 2‰ (2.27 ± 0.63 μm) and 8‰ (1.87 ± 0.44 μm) salinity and control (1.66 ± 0.56 μm) (p < 0.05). The results showed 2‰ and 4‰ salinity supported higher numbers of motile B. plicatilis and higher larval survival and growth rate to 11 DPH.

Using cell cycle measurements with flow cytometry to predict the growth rate of Walleye Pollock Gadus chalcogrammus larvae

Growth rate during early life stages can be an important factor in the recruitment process of marine fishes, and in this study we develop a methodology based on cell cycle measurements to predict the growth rate of Walleye Pollock (Gadus chalcogrammus) larvae. Results from cell-cycle analysis of muscle cell nuclei of laboratory-reared Walleye Pollock larvae measured with flow cytometry were used as covariates in a generalized additive model to predict the growth rate (growth in length per day, mm d−1) of individual larvae from the day exogenous feeding began (first feeding) to the time of capture (r2 = 0.79). Additional covariates used were temperature and standard length. A generalized additive model to classify a larva as fast- or slow-growing was also formulated using the same covariates. Validation testing with an independent set of 45 laboratory-reared larvae showed that 33% of the laboratory growth rates (i.e., growth rate based on age and size) fell within the 95% confidence interval of the predicted growth rates, and predicted growth rates were significantly less than otolith-derived growth rates. The growth classification model was more accurate than the growth rate model, correctly classifying the growth rate type (fast or slow growing) of 71% of the same set of larvae showing that flow cytometric cell cycle analysis may be better suited for classifying larvae as fast- or slow-growing rather than for predicting absolute growth rate. Predicted growth rates for larvae ≤11 mm in length collected from the Gulf of Alaska were within the range of published values for that area, and were not significantly different than corresponding otolith-derived growth rates. The growth rates of Gulf of Alaska larvae >11 mm were overestimated when compared to both otolith-derived growth rates and published values, and that may be due in part because those larvae were outside of the size range used to formulate the model. Predicted growth rate and growth classification of late-stage, field-collected Walleye Pollock larvae would be improved by adding larvae as large as 15 mm to the model to encompass the size range of larvae typically collected during spring ichthyoplankton surveys conducted in the Bering Sea or Gulf of Alaska. Flow cytometric cell cycle analysis offers promise as an alternative method for determining growth rate of fish larvae when otolith daily increments cannot be reliably counted.

Densities, Diets, and Growth Rates of Larval Alewife and Bloater in a Changing Lake Michigan Ecosystem

AbstractVariability in abiotic and biotic factors during larval stages has profound impacts on fish recruitment. In Lake Michigan, where the composition of lower trophic levels has undergone considerable changes in the past decade, managers are concerned that fish recruitment could be negatively affected. We hypothesized that spatial variation in Lake Michigan larval fish density and growth can be explained by various environmental predictor variables. In July 2015, we sampled larval fish and zooplankton at 24 sites (distributed among eight transects) around Lake Michigan. We measured larval fish densities and estimated growth rates and diets of the two most abundant species: the AlewifeAlosa pseudoharengusand BloaterCoregonus hoyi(prey fish that represented 89% and 4% of the total catch, respectively). Larval Alewife densities at a given site ranged from 0 to 42.57 larvae/100 m3, but no explanatory variables explained the variation. Alewife mean growth rate equaled 0.50 mm/d, and fish age and zooplankton density best explained growth variation across sites. Larval Bloater densities ranged from 0 to 1.16 larvae/100 m3, and mean growth rate was 0.21 mm/d. Across all sites, 67% of larval Alewife stomachs were empty, whereas only 16% of Bloater stomachs were empty. Larval fish growth rates observed in our study were at least 40% slower than those reported in previous decades for both Alewife and Bloater. Worsening prey environment for pelagic larvae, such as Alewife and Bloater, during the era of abundant dreissenid mussels could reduce the probability of strong year‐classes, which in turn may affect growth and survival of recreationally important salmonine predators.

Spatiotemporal variability in Newfoundland capelin (Mallotus villosus) larval abundance and growth: Implications for recruitment

We examined larval capelin density and growth dynamics in two relatively unstudied northern coastal embayments of Newfoundland (White Bay and Notre Dame Bay), comparing these larval characteristics to those measured in the annually-surveyed Trinity Bay in order to assess the spatiotemporal variability in larval dynamics and its potential implications on subsequent recruitment. We conducted ichthyoplankton surveys in August of 2015 and 2016, assessing larval density and using otolith microstructure analyses to estimate larval age and growth rates. Size of larvae captured over the two years ranged between 4 and 17 mm, corresponding to an estimated age of 1–33 d. Our results indicated substantial spatial and interannual variability in both density and growth. Larval density was similar between bays in 2015 but drastically different in 2016, where the northern bays were characterized by an order of magnitude less larvae than Trinity Bay. Larval growth was significantly higher in the northern bays in 2015, but lower in 2016, relative to Trinity Bay. This spatiotemporal variability in growth, abundance, and survival potential of larval capelin indicates that the proportion of recruits originating from these key spawning areas fluctuates interannually, with potential implications for the assessment and management of the stock.

Macroevolutionary patterns in overexpression of tyrosine: An anti‐herbivore defence in a speciose tropical tree genus, Inga (Fabaceae)

Abstract Plant secondary metabolites are a key defence against herbivores, and their evolutionary origin is likely from primary metabolites. Yet for this to occur, an intermediate step of overexpression of primary metabolites would need to confer some advantage to the plant. Here, we examine the evolution of overexpression of the essential amino acid, L‐tyrosine and its role as a defence against herbivores. We examined overexpression of tyrosine in 97 species of Inga (Fabaceae), a genus of tropical trees, at five sites throughout the Neotropics. We predicted that tyrosine could act as an anti‐herbivore defence because concentrations of 4% tyrosine in artificial diets halved larval growth rates. We also collected insect herbivores to determine if tyrosine and its derivatives influenced host associations. Overexpression of tyrosine was only present in a single lineage comprising 21 species, with concentrations ranging from 5% to 20% of the leaf dry weight. Overexpression was pronounced in expanding but not in mature leaves. Despite laboratory studies showing toxicity of L‐tyrosine, Inga species with tyrosine suffered higher levels of herbivory. We therefore hypothesize that overexpression is only favoured in species with less effective secondary metabolites. Some tyrosine‐producing species also contained secondary metabolites that are derived from tyrosine: tyrosine‐gallates, tyramine‐gallates and DOPA‐gallates. Elevated levels of transcripts of prephenate dehydrogenase, an enzyme in the tyrosine biosynthetic pathway that is insensitive to negative feedback from tyrosine, were found only in species that overexpress tyrosine or related gallates. Different lineages of herbivores showed contrasting responses to the overexpression of tyrosine and its derived secondary metabolites in their host plants. Synthesis. We propose that overexpression of some primary metabolites can serve as a chemical defence against herbivores, and are most likely to be selected for in species suffering high herbivory due to less effective secondary metabolites. Overexpression may be the first evolutionary step in the transition to the production of more derived secondary metabolites. Presumably, derived compounds would be more effective and less costly than free tyrosine as anti‐herbivore defences.

Terminalia catappa leaf extract is an effective rearing medium for larviculture of gouramis

ABSTRACTGouramis require soft and acidic waters for optimal development, and in this context, a cheap and effective culture medium is required. In this study, Pearl and Blue gourami larvae were raised in Terminalia catappa leaf extract (TCE), clear water, and green water, the latter containing 1 × 105 cells/ml Chlorella from Tilapia cultures. Larval survival and specific growth rate (SGR) were determined after 10 days of incubation. TCE was most effective in promoting survival of both gourami species, with the number of viable larvae augmented twofold and 30% in comparison to clear water and green water respectively. TCE was acidic, and this may have played a significant role in boosting survival, although larvae potentially benefited from the antioxidant and therapeutic properties of TCE. TCE significantly boosted growth, as evidenced by a significant increase in the specific growth rate, perhaps explained by the occurrence of additional live food such as Paramecium, Colpidium, and other infusorians. Although the effects of TCE are uncertain, its application enhanced larval performance of gouramis and perhaps blackwater fishes, a finding with potential application in aquaculture.

Rapid larval growth is costly for post-metamorphic thermal performance in a Great Barrier Reef fish

Most marine fish species disperse during a planktonic larval stage where individuals exhibit variation in pelagic duration, growth rate and settlement size. Extreme predation risk is predicted to select for rapid growth rates and decreased pelagic duration as a strategy for increasing survival to settlement. How larval traits affect post-metamorphic performance, however, has been a contentious topic over the past 50 yrs. Some studies suggest that larval traits have carry-over effects to later life stages, where larval traits can be positively or negatively correlated with post-metamorphic performance. For example, individuals with rapid larval growth rates may settle at larger sizes and have faster post-metamorphic locomotion than slow-growing individuals. Alternatively, trade-offs between life stages might exist, where rapid larval growth rate may be negatively correlated with post-metamorphic locomotion, potentially due to energetic resource allocation trade-offs. In addition, other studies suggest that larval traits are decoupled from later life stages to allow for a transition in morphology and habitat. We tested how Bathygobius cocosensis hatch size, larval growth rates, settlement size and pelagic duration correlated with post-metamorphic thermal performance of burst swimming speed, routine metabolic rate and critical thermal maximum. We found that larval growth rate was negatively correlated with juvenile routine metabolic rate and burst swimming speed across a range of test temperatures. That is, fast-growing larvae had slower burst swimming speeds and lower routine metabolic rates across temperature as juveniles compared to slower-growing larvae. We also found that hatch size and pelagic larval duration were not correlated with post-metamorphic performance. Thus, we provide evidence both for larval traits having carry-over effects on later life stages and also for larval traits being decoupled with thermal performance post-metamorphosis. This is the first study to show that rapid larval growth rate is costly for post-metamorphic thermal performance.

Biotoxicity of diclofenac on two larval amphibians: Assessment of development, growth, cardiac function and rhythm, behavior and antioxidant system

The non-steroidal anti-inflammatory drug diclofenac (DCF) threatens the health of aquatic animals and ecosystems. In the present study, different biological endpoints (mortality, development and growth, abnormalities, cardiotoxicity, neurotoxicity and antioxidant system) were used to characterize the acute and chronic effects of DCF (at concentrations ranging between 125 and 4000 μg L−1) on two amphibian species from Argentina (Trachycephalus typhonius and Physalaemus albonotatus). Results showed that the larval developmental, growth rates, and body condition of DCF-exposed individuals of both species were significantly reduced. DCF-exposed individuals also showed several morphological abnormalities, including significantly altered body axis, chondrocranium and hyobranchial skeleton, and organ and visceral abnormalities including cardiac hypoplasia, malrotated guts, asymmetrically inverted guts, and cholecystitis. DCF also had a significant effect on the swimming performance of both species: at low concentrations (125 and 250 μg L−1), swimming distance, velocity and global activity decreased, whereas, at high concentrations (1000 and 2000 μg L−1), these behavioral responses increased. Regarding cardiac function and rhythm, at DCF concentrations higher than 1000 μg L−1, the heart frequency and ventricular systole interval of both species were significantly reduced. Regarding the antioxidant system, the activity of acetylcholinesterase indicated that DCF is neurotoxic and thus related to the changes in behavioral performance. The DCF concentrations studied produced a biochemical imbalance between radical oxygen species production and antioxidant systems. The sensitivities to sublethal and chronic DCF exposure in both anuran species were similar, thus indicating the inherent complexity involved in understanding the biotoxic effects of DCF.

Additive bioenergetic responses to a pesticide and predation risk in an aquatic insect

Ignoring natural stressors such as predation risk may contribute to the failure of ecological risk assessment of pesticides to protect freshwater biodiversity. To better understand combined effects of multiple stressors, bioenergetic responses are important as these inform about the balance between energy input and consumption, and provide a unifying mechanism to integrate the impact of multiple stressors with different modes of action. We studied in Enallagma cyathigerum damselfly larvae the single and combined effects of exposure to the pesticide chlorpyrifos and predation risk on life history (survival and growth rate) and bioenergetic response variables at the organismal level (assimilation and conversion efficiency) and the cellular level (cellular energy allocation CEA, energy storage Ea, and energy consumption Ec). Chlorpyrifos exposure almost halved the survival of the damselfly larvae, while predation risk had no effect on survival. Both exposure to the pesticide and to predation risk reduced larval growth rates. This was caused by a reduced conversion efficiency under chlorpyrifos exposure, and by a reduced assimilation efficiency under predation risk. Both chlorpyrifos and predation risk reduced the CEA because of a decreased Ea, and for chlorpyrifos also an increased Ec. The lower Ea was driven by reductions in the fat and glycogen contents. Effects of the pesticide and predation risk were consistently additive and for most variables the strongest response was detected when both stressors were present. The absence of any synergisms may be explained by the high mortality and hypometabolism caused by the pesticide. Our results indicate that CEA can be a sensitive biomarker to evaluate effects of not only contaminants but also natural stressors, such as predation risk, and their combined impact on organisms.

Latitudinal Growth Variation in Young Tautogs: A Field, Laboratory, and Growing Degree‐Day Assessment of Potential Intrinsic Differences in Growth Responses to Temperature

AbstractA difference in size at age of young Tautogs Tautoga onitis has been reported from two sites in the Mid‐Atlantic Bight, USA, whereby southern fish (Virginia [VA]) reach a twofold greater size than northern fish (Rhode Island [RI]) by age 1 but grow at similar size‐dependent annual rates thereafter. We investigated the basis for this difference by using a coordinated field, laboratory, and growing degree‐day (GDD) approach. Age‐0 Tautogs were sampled from three locations (Chesapeake Bay, VA; Delaware Bay, Delaware [DE]; and Narragansett Bay, RI) and showed a clinal relationship of decreasing fish size and growth rate with increasing latitude. Otolith‐based estimates of larval stage duration and growth rate showed no significant clinal relationship. Young Tautogs from these locations were reared in common‐garden experiments (at 5, 15, and 25°C) to determine whether there were intrinsic postsettlement growth differences related to temperature. None of the location‐specific groups of age‐0 Tautogs exhibited growth that was consistently faster than that of Tautogs from the other locations over all temperatures examined. These data and the results of a GDD assessment between VA and RI indicate that latitudinal differences in temperature regime and growing season length are the major factors determining latitudinal growth differences in age‐0 fish. However, age‐1 RI fish of equivalent size grew significantly faster than age‐0 RI and DE fish and similar to age‐0 VA fish at 15°C and grew 40% faster than all age‐0 fish at 25°C, suggesting countergradient growth variation in age‐1 and older northern Tautogs. Size‐selective overwinter mortality of age‐0 northern fish—whereby smaller individuals are most susceptible to low temperature—is proposed as the likely underlying mechanism leading to faster growth of older northern fish at temperature. Such a mechanism would at least partially compensate for the lower temperature and shorter growing season at higher latitudes.

Larval development, juvenile survival, and burrowing rate of geoduck clams (Panopea japonica) under different pH conditions

Changes in seawater pH in the culture environment have numerous effects on marine bivalves. To investigate the effect of pH on larval development, juvenile survival, and burrowing rate of geoduck clams (Panopea japonica), specimens were cultured under different experimental pH conditions (6.8, 7.2, 7.6, 8.0, 8.4, and 9.2). The pH range for optimal growth and development differed among different larval stages. However, significant changes in larval development (p < 0.5) relative to the control (pH 8.0) were detected at very high or low pH. The best hatching rate occurred at pH 7.6–8.8, and it was significantly lower (p < 0.5) at pH 6.8, 7.2, and 9.2. Larval survival was only 4% at pH 6.8. Growth rate of larvae increased with increasing pH and the optimal range was 8.0 to 8.8. This finding suggests that alkaline conditions favor growth and development of larvae and allow them to reach the metamorphic stage promptly. Prolonged metamorphosis was a common feature in larvae in the different experimental pH groups. pH below 7.6 and above 8.8 resulted in a significantly (p < 0.5) lower metamorphosis rate, suggesting that high acidity and alkalinity were deleterious to larval metamorphosis. Thus, the suitable pH range for metamorphosis was 8.0 to 8.8. Lower and higher pH also affected the digging behavior of geoduck clams, and the suitable pH range for burrowing was 7.2 to 8.8. Geoduck clams stopped burrowing in the sand at pH 6.8 and 9.2, possibly due to impairment of biological process caused by acidic and alkaline seawater. These findings provide valuable information about the larval and juvenile responses of P. japonica in variable pH.

Trends in Sandeel Growth and Abundance off the East Coast of Scotland

Sandeels Ammodytes marinus are a crucial forage fish species in the North Sea, transferring zooplankton energy to higher trophic levels. However, there has been a sustained decline in sandeel abundance in the northwestern North Sea since 2000. Here we use field data to analyze year-to-year changes in A. marinus growth rate between 1997 and 2009 and assess whether variation in growth rate corresponded with variation in abundance. The signature of the reduction in abundance between 2000 and 2009 was a decline in age 1 sandeels, while no other age class declined. Analysis of age-length data showed that the decline in abundance coincided with a period of low growth. Growth performance indexes were correlated with zooplankton and phytoplankton biomass but not temperature. Further, we observed a significant correlation between larval growth rate and 0-group sandeel length during a period when hatch dates were relatively fixed; suggesting recent changes in length were influenced by food availability.