Low Food Rations Research Articles

Variable food alters responses of larval crown-of-thorns starfish to ocean warming but not acidification

Phytoplankton abundance is decreasing and becoming more variable as the ocean climate changes. We examine how low, high, and variable phytoplankton food supply affected the survival, development, and growth of larval crown-of-thorns starfish, Acanthaster sp. exposed to combined warming (26, 30 °C) and acidification (pH 8.0, 7.6). Larvae fed a low food ration are smaller, and develop slower and with more abnormalities than larvae fed a high ration. Larvae fed a variable food supply (low, followed by high ration) overcome the negative effects of low food on development rate and occurrence of abnormalities, but are 16–17% smaller than larvae fed the high ration continuously. Acidification (pH 7.6) slows growth and development and increases abnormalities regardless of the food regime. Warming slows growth and development, but these effects are mitigated by high food availability. As tropical oceans warm, the success of crown-of-thorns starfish larvae may depend on the abundance of their phytoplankton prey.

Sirtuin-dependent recovery from aerial heat shock: The effects of food ration, thermal history, and sirtuin inhibition on clearance rates and valve gape activity of the California mussel, Mytilus californianus (Conrad)

Intertidal mussels regularly experience seasonal fluctuations in food availability and heat stress over the course of a tidal cycle, yet little is known about the biochemical mechanisms linking food ration and thermal tolerance, despite evidence that food enhances stress tolerance at the organismal level. We hypothesized that sirtuins (food-dependent protein regulators of cellular homeostasis), which may regulate the cellular stress response of mytilids during heat stress, also affect organismal performance during recovery from heat stress. As part of a broader study, we investigated the effects of acclimation food ration, acclimation emersion (air) temperature, and sirtuin inhibitors on the feeding behavior of the California mussel, Mytilus californianus, during recovery from acute aerial heat shock. Mussels were acclimated for 3 wk. to either a low (0.25% algae·g mussel dry wt−1) or high (1.5% algae·g mussel dry wt−1) algal ration and low (20 °C) or high (30 °C) emersion temperatures, in tidal simulator tanks capable of maintaining standard circadian and circatidal rhythms. Following acclimation, mussels were exposed to two sirtuin inhibitors (nicotinamide and suramin) or no inhibitors for one high tide cycle. During the subsequent low tide cycle, all mussels were exposed to an acute aerial heat shock (33 °C) and then allowed to recover in their respective acclimation conditions. Every 12 h during the 48 h before sirtuin inhibition and 48 h following acute heat shock (in the corresponding high tide periods), we recorded clearance rates and valve gape activity. Mussels acclimated to a low food ration significantly reduced clearance rates with heat shock and sirtuin inhibition, but not with heat shock alone, relative to pre-treatment values regardless of emersion temperature. Mussels acclimated to a low food ration and high emersion temperature showed significant reductions in valve gape activity following an acute heat shock following sirtuin inhibition, but not in any of the other acclimation groups. Unexpectedly, heat shock alone reduced clearance rates of mussels acclimated to high food and high emersion temperatures only, without any additional effect by heat shock and sirtuin inhibition. Together, these findings suggest an important role for sirtuins at the organismal level during recovery from heat shock following acclimation to a low food ration.

Effects of methylmercury on the early life stages of an estuarine forage fish using two different dietary sources

Marine fish accumulate methylmercury (MeHg) to elevated concentrations, often higher than in freshwater systems. As a neurotoxic compound, high MeHg tissue concentrations could affect fish behavior which in turn could affect their populations. We examined the sublethal effects of MeHg on larvae of the Sheepshead minnow (Cyprinodon variegatus), an estuarine fish, using artificial or natural diets with varying MeHg concentrations (0–4.8 ppm). Larvae were fed control and MeHg-contaminated diets at low or normal (10% of their body mass) daily food rations from 7 to 29 days when they reached juvenile stage. Growth, respiration, swimming activity and prey capture ability were assessed. Food ration affected Hg toxicity in our study. Natural diets containing 3.2 ppm MeHg had no impacts on growth and swimming in fish that were fed normal food rations but depressed growth and swimming at low food rations. MeHg toxicity did not differ between artificial and natural foods, however fish accumulated more MeHg from the former. Artificial food containing 4.8 ppm MeHg only affected prey capture after 21 days of exposure. Sheepshead minnows, a forage fish species occupying a low trophic level in coastal waters, can be MeHg tolerant, especially when food is abundant, and can serve as an enriched Hg source for higher trophic level predators.

The Effect of Dietary Exposure to Coal Ash Contaminants within Food Ration on Growth and Reproduction in Daphnia magna.

Coal ash contains numerous contaminants and is the focus of regulatory actions and risk assessments due to environmental spills. We exposed Daphnia magna to a gradient of coal ash contamination under high and low food rations to assess the sublethal effects of dietary exposures. Whereas exposure to contaminants resulted in significant reductions in growth and reproduction in daphnids, low, environmentally relevant food rations had a much greater effect on these endpoints. Environ Toxicol Chem 2020;39:1998-2007. © 2020 SETAC.

Differences in mitochondrial efficiency explain individual variation in growth performance.

The physiological causes of intraspecific differences in fitness components such as growth rate are currently a source of debate. It has been suggested that differences in energy metabolism may drive variation in growth, but it remains unclear whether covariation between growth rates and energy metabolism is: (i) a result of certain individuals acquiring and consequently allocating more resources to growth, and/or is (ii) determined by variation in the efficiency with which those resources are transformed into growth. Studies of individually housed animals under standardized nutritional conditions can help shed light on this debate. Here we quantify individual variation in metabolic efficiency in terms of the amount of adenosine triphosphate (ATP) generated per molecule of oxygen consumed by liver and muscle mitochondria and examine its effects, both on the rate of protein synthesis within these tissues and on the rate of whole-body growth of individually fed juvenile brown trout (Salmo trutta) receiving either a high or low food ration. As expected, fish on the high ration on average gained more in body mass and protein content than those maintained on the low ration. Yet, growth performance varied more than 10-fold among individuals on the same ration, resulting in some fish on low rations growing faster than others on the high ration. This variation in growth for a given ration was related to individual differences in mitochondrial properties: a high whole-body growth performance was associated with high mitochondrial efficiency of ATP production in the liver. Our results show for the first time, to our knowledge, that among-individual variation in the efficiency with which substrates are converted into ATP can help explain marked variation in growth performance, independent of food intake. This study highlights the existence of inter-individual differences in mitochondrial efficiency and its potential importance in explaining intraspecific variation in whole-animal performance.

Deciphering the effect of food availability, growth and host condition on disease susceptibility in a marine invertebrate.

Food provisioning influences disease risk and outcome in animal populations in two ways. On the one hand, unrestricted food supply improves the physiological condition of the host and lowers its susceptibility to infectious disease, reflecting a trade-off between immunity and other fitness-related functions. On the other hand, food scarcity limits the resources available to the pathogen and slows the growth and metabolism of the host on which the pathogen depends to proliferate. Here, we investigated how food availability, growth rate and energetic reserves drive the outcome of a viral disease affecting an ecologically relevant model host, the Pacific oyster, Crassostrea gigas We selected fast- and slow-growing animals, and we exposed them to high and low food rations. We evaluated their energetic reserves, challenged them with a pathogenic virus, monitored daily survival and developed a mortality risk model. Although high food levels and oyster growth were associated with a higher risk of mortality, energy reserves were associated with a lower risk. Food availability acts both as an enabling factor for mortality by increasing oyster growth and as a limiting factor by increasing their energy reserves. This study clarifies how food resources have an impact on susceptibility to disease and indicates how the host's physiological condition could mitigate epidemics. Practically, we suggest that growth should be optimized rather than maximized, considering that trade-offs occur with disease resistance or tolerance.

Impacts of temperature and food availability on the condition of larval Arctic cod (Boreogadus saida) and walleye pollock (Gadus chalcogrammus)

AbstractThe Arctic marine environment is rapidly changing with rising sea surface temperatures, declining sea ice habitat and projected increases in boreal species invasions. The success of resident Arctic fish will depend on both their thermal tolerance and their ability to cope with changing trophic interactions. Larval fish energetic condition is closely associated with mortality rates and therefore provides an indicator of overall well-being or fitness. In this study, we experimentally determined larval morphometric and lipid-based condition in an Arctic gadid (Arctic cod, Boreogadus saida) and a boreal gadid (walleye pollock, Gadus chalcogrammus) in response to different temperatures and food rations. Our results suggest that larval condition is highly sensitive to both factors but varies in a species- and ontogenetic-dependent manner. Results indicated that condition metrics based on length–weight relationships were not as sensitive as those based on lipid storage. Further, condition metrics changed with ontogeny and were best used within a developmental stage rather than across developmental stages. As expected, larval condition in first-feeding Arctic cod was higher at colder temperatures (2–5°C) than in the boreal gadid (5–12°C). However, at more developed larval stages the peak condition for Arctic cod was at warmer temperatures (7°C), while walleye pollock had the same thermal optimum as during earlier stages. Arctic cod were more sensitive to food ration at first feeding than walleye pollock, however; at later larval stages both species had a negative condition response to low food ration, especially at elevated temperatures (5 vs. 7°C). The lower thermal tolerance of Arctic cod, coupled with a higher sensitivity to food availability indicates that Arctic cod are particularly vulnerable to on-going environmental change. Arctic cod is a lipid-rich keystone species and therefore a reduction in their energetic condition during summer has the potential to affect the health of higher trophic levels throughout the Alaskan Arctic.

How to handle ‘poor’ foodstuffs: Acclimation of the common cockle (Cerastoderma edule) to detrital diets

As an approach to elucidating the “value” of detritus as a food source for bivalves, we analysed the capability of the common cockle (Cerastoderma edule) to modulate feeding and digestive rates during acclimation to low and high food rations of detrital diets with either low (Juncus maritimus) or high digestibility (Enteromorpha spp.). On acclimation day 3, feeding rates were similar in cockles fed different detrita; however, the absorption rate was higher in cockles fed Enteromorpha spp. With J. maritimus, rising food rations promoted an exponential decrease in absorption efficiency, whereas with Enteromorpha spp., absorption efficiency was only marginally reduced. During acclimation, cockles improved the rate at which both detritus were assimilated by means of increasing ingestion rates while maintaining absorption efficiency. When the time-course of digestive carbohydrase activities was monitored during acclimation to either detritus or phytoplankton (Isochrysis galbana), we found that only phytoplankton promoted the induction of cellulase activity in the digestive glands of cockles. This response in cockles fed phytoplankton promoted an increase in the digestibility of Enteromorpha spp., but had no effect on the digestibility of J. maritimus.

Food ration does not influence the effect of elevated CO2 on antipredator behaviour of a reef fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 586:155-165 (2018) - DOI: https://doi.org/10.3354/meps12397 Food ration does not influence the effect of elevated CO2 on antipredator behaviour of a reef fish Shannon J. McMahon1,2,*, Jennifer M. Donelson2, Philip L. Munday2 1College of Marine and Environmental Science, and 2ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia *Corresponding author: shannon.mcmahon@jcu.edu.au ABSTRACT: The appropriate behavioural response to predation risk is critical to survival; however, behavioural responses can be subjected to trade-offs. For example, individuals may engage in riskier foraging behaviour to secure sufficient energy if resources are limited. Additionally, elevated CO2 can influence foraging and antipredator behaviour of marine organisms. Yet, how the availability of energetic resources may influence antipredator behaviour in an elevated CO2 environment is unknown. We tested the effects of food ration (low and high: 4 and 8% of body weight per day, respectively) on antipredator behaviour at ambient (489 µatm) and elevated (1022 µatm) CO2 in juvenile Amphiprion percula at 50 d post-hatching. Juveniles were from parents held at either ambient or elevated CO2, as parental exposure can influence phenotypic response in offspring. Antipredator behaviour was severely impaired by elevated CO2, with juveniles reared at elevated CO2 exhibiting no change in feeding rate in the presence of the predator cue compared with a >67% reduction in feeding rate in ambient CO2 fish. By contrast, food ration had a minor effect on the change in feeding rate in response to the predator cue, with only a 2.3% difference between high and low food ration fish. The effect of elevated CO2 on antipredator behaviour of juveniles was not influenced by food ration. Parental exposure to elevated CO2 influenced the baseline feeding rate and exhibited a small carry-over effect in elevated CO2 juveniles. These results suggest that reef fish could exhibit riskier behaviour at elevated CO2 levels, regardless of the energetic resources available. KEY WORDS: Ocean acidification · Energy budget · Predation · Trade-offs · Parental effects · Climate change Full text in pdf format Supplementary material PreviousNextCite this article as: McMahon SJ, Donelson JM, Munday PL (2018) Food ration does not influence the effect of elevated CO2 on antipredator behaviour of a reef fish. Mar Ecol Prog Ser 586:155-165. https://doi.org/10.3354/meps12397 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 586. Online publication date: January 11, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Plasticity and personality of parental care in the clown anemonefish

Characterizing individual variation in parental care is critical to understanding how selection shapes and maintains patterns of care, yet little is known about how individual parents vary in their responses to the environment. Reaction norms, functions that describe how phenotypes change across an environmental gradient, provide an elegant framework for studying individual variation in behavioural responses. We use a reaction norm approach to investigate how studying plasticity, which describes variation within an individual through time, and personality, which describes repeatable variation among individuals, together explain individual variation in the parental behaviour of the anemonefish Amphiprion percula. More specifically, we test how resource availability influences individual parental responses to the environment and discuss the consequences for our understanding of plasticity and personality in parental care. Breeding pairs of A. percula were fed either a high or a low food ration and their parental behaviours were monitored. Individuals exhibited plasticity in parental behaviour across the two resource environments. Furthermore, individuals were repeatable in their behaviour through time, as evidenced by significant among-individual variation in intercept. Finally, the slope and elevation of individual reaction norms varied, revealing a level of variation not captured at the population level and providing insight into the potential mechanisms generating individual variation.

Standardized toxicity testing may underestimate ecotoxicity: Environmentally relevant food rations increase the toxicity of silver nanoparticles to Daphnia.

Daphnia in the natural environment experience fluctuations in algal food supply, with periods when algal populations bloom and seasons when Daphnia have very little algal food. Standardized chronic toxicity tests, used for ecological risk assessment, dictate that Daphnia must be fed up to 400 times more food than they would experience in the natural environment (outside of algal blooms) for a toxicity test to be valid. This disconnect can lead to underestimating the toxicity of a contaminant. We followed the growth, reproduction, and survival of Daphnia exposed to 75 and 200 µg/L silver nanoparticles (AgNPs) at 4 food rations for up to 99 d and found that AgNP exposure at low, environmentally relevant food rations increased the toxicity of AgNPs. Exposure to AgNP at low food rations decreased the survival and/or reproduction of individuals, with potential consequences for Daphnia populations (based on calculated specific population growth rates). We also found tentative evidence that a sublethal concentration of AgNPs (75 µg/L) caused Daphnia to alter energy allocation away from reproduction and toward survival and growth. The present findings emphasize the need to consider resource availability, and not just exposure, in the environment when estimating the effect of a toxicant. Environ Toxicol Chem 2017;36:3008-3018. © 2017 SETAC.

Is behaviour in a novel environment associated with bodily state in brown troutSalmo truttafry?

AbstractEnergetic status and body size are inconstant bodily states often considered to have feedback effects on behaviour. Feedbacks can be negative, like starvation‐threshold feedbacks (lower state values = increased risk taking due to higher energy need, and vice versa), or positive, like state‐dependent safety feedbacks (higher state values = lower vulnerability when expressing risky behaviours, and vice versa). Few studies have investigated feedback effects during the early‐life survival bottleneck of territorial species, when rapid growth is particularly important to maintain competitive ability. We investigated effects of body size and energetic status on the emergence latency into an unknown environment in highly territorial brown trout fry. We manipulated energetic status using high and low food rations in different combinations over two consecutive periods. In contrast to results from other small‐sized fishes, no general behavioural effects of energetic state were detected, but larger fish had on average shorter emergence latency. Starvation‐threshold feedbacks were not supported, but the size effect favours the presence of a state‐dependent safety feedback. When individuals were split into clusters characterised by long (>34 s) and short (<34 s) emergence latency, a state‐dependent safety feedback, based on energetic status, was found in the short‐latency cluster. Positive state‐dependent feedbacks may reflect the high level of competition among wild trout fry during the first summer, particularly among the more active individuals (i.e., from the short latency cluster). High state levels could be utilised to gain advantages over lesser competitors (e.g., to establish territories), particularly if the overall risk of starvation is higher than the risk of predation.

Food regime modulates physiological processes underlying size differentiation in juvenile intertidal mussels Mytilus galloprovincialis

Feeding and growth experiments were conducted to test the hypothesis that physiological attributes responsible for size differentiation among bivalves likely vary with environmental conditions. Juvenile mussels (Mytilus galloprovincialis) were collected from an intertidal population in Biscay, Spain (43°24′42,462″N02°56′43,659″W), in January 2007 and 2009. These mussels were maintained in the laboratory under either restrictive or optimal feeding conditions until fast- and slow-growing individuals on each maintenance regime could be identified. After fast- and slow-growing individuals were identified, the components of energy balance responsible for such growth rate differences were measured. The analysis of physiological traits indicates that under optimal food supply conditions, the capacity to ingest and absorb food and associated costs of growth are the main factors underlying growth rate differences. The set of physiological differences changed when size differentiation took place under restrictive food conditions. Higher rates of absorption coupled with reduced rates of metabolism accounted for faster growth in this case, especially under low food rations.

Daphnia magna's sense of competition: intra-specific interactions (ISI) alter life history strategies and increase metals toxicity.

This work investigates whether the scale-up to multi-animal exposures that is commonly applied in genomics studies provides equivalent toxicity outcomes to single-animal experiments of standard Daphnia magna toxicity assays. Specifically, we tested the null hypothesis that intraspecific interactions (ISI) among D. magna have neither effect on the life history strategies of this species, nor impact toxicological outcomes in exposure experiments with Cu and Pb. The results show that ISI significantly increased mortality of D. magna in both Cu and Pb exposure experiments, decreasing 14 day LC50 s and 95 % confidence intervals from 14.5 (10.9–148.3) to 8.4 (8.2–8.7) µg Cu/L and from 232 (156–4810) to 68 (63–73) µg Pb/L. Additionally, ISI potentiated Pb impacts on reproduction eliciting a nearly 10-fold decrease in the no-observed effect concentration (from 236 to 25 µg/L). As an indication of environmental relevance, the effects of ISI on both mortality and reproduction in Pb exposures were sustained at both high and low food rations. Furthermore, even with a single pair of Daphnia, ISI significantly increased (p < 0.05) neonate production in control conditions, demonstrating that ISI can affect life history strategy. Given these results we reject the null hypothesis and conclude that results from scale-up assays cannot be directly applied to observations from single-animal assessments in D. magna. We postulate that D. magna senses chemical signatures of conspecifics which elicits changes in life history strategies that ultimately increase susceptibility to metal toxicity.Electronic supplementary materialThe online version of this article (doi:10.1007/s10646-016-1667-1) contains supplementary material, which is available to authorized users.

Autumn food restriction reduces smoltification rate, but not over‐winter survival, in juvenile brown trout Salmo trutta

AbstractThe winter is often considered as a survival bottleneck for stream‐living fish. Juvenile salmonids generally become less active during this period, and while food intake continues to some extent, growth rates are typically low. Here we present the results of an over‐winter field experiment where energy levels were manipulated in late autumn. Three groups of juvenile (age 1+) brown trout, from an anadromous population, were monitored with respect to over‐winter growth rate and survival (as indicated by recapture rates). Two groups were fed either high (HR), or low (LR) food rations in the laboratory for a month (October); the third group remained in the stream (STR). Over‐winter growth rates were relatively low in all groups, and no growth compensation could be detected. Compared to HR and LR, STR fish had higher recapture rates after winter, indicating that laboratory housing may have affected the subsequent stream survival negatively. Comparing the two laboratory‐housed groups, the LR group reached similar condition as the HR group in early spring, without indications of differences in survival. However, the initiation rate of body silvering (indicating initiation of smoltification) was lower in the LR group. Thus, it appears that food restriction during late autumn affect the onset of smoltification in juvenile brown trout. The results support previous laboratory studies indicating that salmonids modify their over‐winter foraging behaviour to avoid too low energy levels at the end of winter. This modification appears to delay smoltification, but may not necessarily be costly in terms of over‐winter mortality.

Food availability in spring affects smolting in brown trout (Salmo trutta)

Prior to out-migration, salmonid fish typically undergo physiological and morphological changes — a process known as smolting. This study indicates that smolting in brown trout (Salmo trutta) is affected by feeding conditions in spring immediately prior to out-migration. This conclusion was reached after experimentally testing the effect of seasonal variation in food availability on smolt status in the spring. A migratory strain of trout was administered either high or low food rations in the autumn, winter, or spring prior to release in the spring. While fish growth or condition could be affected in any season, it was spring rationing that reduced growth and growth-related variables and that caused increased smolting. Our result supports the idea that smoltification and the decision to migrate is affected by spring food availability regardless of conditions in the previous autumn or winter.

Effect of food availability on the growth and thermal physiology of juvenile Dungeness crabs (Metacarcinus magister)

Juvenile Dungeness crabs spend ~1 year in the San Francisco Estuary, where they undergo considerable growth before returning to the coastal ocean. Previous studies suggest that competition, food scarcity and avoidance of conspecifics may cause some juvenile Dungeness crabs in the San Francisco Estuary to become food limited. Food limitation may force these crabs to forage in higher temperature intertidal environments in the estuary, exposing them to stressful conditions in order to sustain growth and, potentially, necessitating physiological trade-offs in energy allocation between growth and stress tolerance. To investigate the effects of food limitation on aerobic metabolism and physiological performance of crabs, we assessed growth, moulting frequency, metabolic rate, citrate synthase and malate dehydrogenase enzyme activity and cardiac performance, as an index of temperature sensitivity and upper temperature tolerance. Summer- and winter-caught crabs were acclimated to either a high- or a low-food ration for 5 weeks. Overall, our results demonstrated that while food limitation had a negative effect on growth of juvenile Dungeness crabs in both the summer and the winter feeding trials, crabs in the low-food group maintained both metabolic rate at ambient San Francisco Estuary temperatures (15°C; summer trial only) and upper temperature tolerance as determined by failure of cardiac function when compared with crabs in the high-food group (summer and winter trials). Therefore, the ability to maintain stress tolerance when food is limited appears to come as a physiological trade-off to growth. Food-limited crabs were unable to increase their metabolic rate to the same level as that achieved by well-fed crabs; therefore, if exposure to elevated temperatures persists and requires more energy than can be met by crabs in their food-limited state, physiological performance may be compromised.

Temperature and food availability affect risk assessment in an ectotherm

Risk assessment in ectotherms is strongly affected by an organism's energy expenditure and acquisition because these will alter the motivation to feed, which is balanced against antipredator behaviours. Temperature and food availability are known to affect the physiological condition of ectotherms, but how interactions between these variables may influence predator–prey dynamics is still poorly understood. This study examined the interactive effects of food availability and temperature on the trade-offs between predator avoidance behaviour and foraging in juveniles of a marine damselfish, Pomacentrus chrysurus. Predator avoidance behaviour was tested by exposing fish to chemical alarm cues obtained from skin extract of conspecifics. When detected, these cues elicit an antipredator response in fish, typically characterized by decreased foraging. Fish maintained under high food ration displayed distinct antipredator responses to chemical alarm cues, regardless of temperature. However, fish maintained in conditions of low food ration and 3 °C above ambient temperature did not display an antipredator response when exposed to chemical alarm cues, whereas those in ambient temperature did. These results suggest that individuals in low physiological condition because of limited food availability are more susceptible to increased temperature and may therefore take greater risks under predation threats to satisfy their energetic requirements.

Developmental plasticity of growth and digestive efficiency in dependence of early-life food availability.

Nutrition is a potent mediator of developmental plasticity. If food is scarce, developing organisms may invest into growth to outgrow size-dependent mortality (short-term benefit) and/or into an efficient digestion system (long-term benefit). We investigated this potential trade-off, by determining the influence of food availability on juvenile body and organ growth, and on adult digestive efficiency in the cichlid fish Simochromis pleurospilus. We reared two groups of fish at constant high or low food rations, and we switched four other groups between these two rations at an early and late juvenile period. We measured juvenile growth and organ sizes at different developmental stages and determined adult digestive efficiency. Fish kept at constant, high rations grew considerably faster than low-food fish. Nevertheless, S. pleurospilus partly buffered the negative effects of low food availability by developing heavier digestive organs, and they were therefore more efficient in digesting their food as adults. Results of fish exposed to a ration switch during either the early or late juvenile period suggest (i) that the ability to show compensatory growth after early exposure to low food availability persists during the juvenile period, (ii) that digestive efficiency is influenced by varying juvenile food availability during the late juvenile phase and (iii) that the efficiency of the adult digestive system is correlated with the growth rate during a narrow time window of juvenile period.

Effects of food ration on growth and development of ovary and energy budgets of Gambusia affinis

This study investigated the effects of food ration on growth and development of ovary and energy budgets of female Gambusia affinis from 25-day post-hatch(DPH) to first sexual maturity.The 25-day old G.af-finis with oocytes with the slowest growth stages were selected randomly,and placed in aquarium cages in the laboratory at(27.5±0.5)℃,and given three food ration levels(low,medium and high [repletion]).Environmental adaptability and food supply data were analyzed to identify invasive mechanisms of G.affinis.Results showed that at the onset of sexual maturity,body length,wet mass,fullness,specific growth rate,hepatosomatic index,gona-dosomatic index,numbers of mature eggs and calorific value significantly increased with increasing ration levels.There were no significant differences in dry mass and diameter of mature eggs under different ration conditions.Fish body size at the onset of sexual maturity was minimal with low food ration(average length of 17.98 mm±0.98 mm and average wet weight of 104.41 mg±3.31 mg).Feed conversion efficiencies in dry and wet weights de-creased with increasing ration levels,and feed conversion efficiencies at low ration were significantly higher than those at repletion rations.The proportion of food energy allocated to growth and ovaries increased with decreasing ration levels.The maximum proportion of food energy allocated to growth was 56.22%,and that allocated to ova-ries was 10.42% when low food rations were provided.Thus,when G.affinis were experiencing food shortages,the body sizes of the individuals at first sexual maturity decreased.In addition,feed conversion efficiencies in-creased,and the proportion of food energy allocated to growth and reproduction increased.This physical adapta-tion may be beneficial for G.affinis ecological invasions.