Size Range Of Fish Research Articles

Measurement of mitochondrial respiration in permeabilized fish gills.

ABSTRACTPhysiological investigations of fish gills have traditionally centred on the two principal functions of the gills: gas exchange and ion regulation. Mitochondrion-rich cells (MRCs) are primarily found within the gill filaments of fish, and are thought to proliferate in order to increase the ionoregulatory capacity of the gill in response to environmentally induced osmotic challenges. However, surprisingly little attention has been paid to the metabolic function of mitochondria within fish gills. Here, we describe and validate a simple protocol for the permeabilization of fish gills and subsequent measurement of mitochondrial respiration rates in vitro. Our protocol requires only small tissue samples (8 mg), exploits the natural structure of fish gills, does not require mechanical separation of the gill tissue (so is relatively quick to perform), and yields accurate and highly reproducible measurements of respiration rates. It offers great potential for the study of mitochondrial function in gills over a wide range of fish sizes and species.

Distribution of migratory fish in the stream (depth, velocity, body size, predators)

In order to supplement the available information for the eco-hydraulic approach to designing fish passages, taking into account the taxonomic, dimensional structure, as well as taking into account the presence of predatory fish in the stream, the distribution of migratory fish of the boreal plain faunistic complex (Russian Federation) was studied. Three depth-velocity sections from the shore to the midstream were investigated: 5 m and 27.8 cm/s, 8 m and 44.4 cm/s, 11 m and 55.6 cm/s. Analysis of the migration distribution of fish showed that in the direction from the shore to the midstream, the proportion of representatives of Cyprinidae decreases from 41.8–24.3% and that of Percidae decreases from 25.0–18.4%. For individuals of two groups: the Acipenseridae and Lotidae, Coregonidae and Esocidae, patterns of distribution in the structure of migratory fish are opposite – their share increases with increasing speed and depth characteristics: 23.0–40.2% and 10.2–17.1%, respectively. An assessment of the dimensional structure revealed a feature of increase in the size range of fish from the shore to the midstream: the dominance of small individuals (<10 cm) in the shore area is replaced by the dominance of large fish (> 30 cm) in the area of higher speeds and depths. A significant difference in the distribution for all studied taxonomic fish groups between the shore and the midstream was shown. Thus, it has been established that for Cyprinidae during the migration period, the choice shifts in favour of minimizing energy costs, and the choice to avoid the risk of predation from individuals of the groups: Coregonidae and Esocidae, and also Percidae, shifts in favour of the former. The distribution of perch is influenced by the reduction of energy costs and the simultaneous avoidance of predation and cannibalism. For the fish group Acipenseridae and Lotidae, their predominance in the deeper area is due to their less developed visual orientation mechanism in the stream because they are bottom-living fish species.

Comparing fishway designs for application in a large tropical river system

River infrastructure poses a serious threat to diverse and productive fish stocks in many tropical river-floodplain systems; particularly the Lower Mekong River, where the fisheries are vital for food security. Dams and weirs block fish migration pathways and prevent access to feeding, spawning or nursery habitat. Fishways are becoming increasingly important for mitigating the effects of barriers; however, knowledge regarding their effectiveness for the biodiverse tropical river systems is still scant. This study examined the effectiveness of differing low-cost fishway designs for rehabilitating degraded floodplain fisheries in the Lower Mekong Basin (LMB) in Laos: (1) vertical slot; (2) submerged orifice — 150 mm square opening; and (3) submerged orifice — 300 mm square opening. Day and night in situ field experiments were undertaken to compare the abundance, biomass, species richness and size range of fish able to pass through each design with relatively low drops between pools (i.e. 150 mm each) and low water velocities (i.e. 1.71 ms−1). Passage of a total of 73 species was supported by the fishway designs at a similar abundance, biomass, species richness and size range of fish, during both the day and night; although, the vertical slot design supported a different suite of fish species to that of the other two designs during the day. This suggests that each of these fishway designs could be successfully used to support the rehabilitation of fisheries in the LMB and potentially other large tropical river systems with relatively diverse migratory fish communities and variable hydrological characteristics. However, the vertical slot provides greater design and operational flexibility over the submerged orifice designs particularly in tropical systems with inherently variable hydrology. The final fishway design choice ultimately depends on the fish species and size classes being prioritised for restoration and the unique hydrological characteristics of the site.

Combination of a sorting grid and a square mesh panel to optimize size selection in the North-East Arctic cod (Gadus morhua) and redfish (Sebastes spp.) trawl fisheries

Abstract Sorting grids and square mesh panels are the two most-applied technical devices to supplement codend size- and species-selection in demersal trawls. In the Barents Sea gadoid fishery, the compulsory size-selectivity system comprises a mesh section with a sorting grid followed by a diamond mesh codend. We tested the size-selective performance of a new sorting section that comprised a sorting grid combined with a square mesh panel as a potential alternative for the grid sections currently in use. The new sorting section was shorter and therefore more maneuverable than the existing sorting grid sections. The investigation was carried out on cod and the bycatch species redfish. The grid was found to contribute to the largest proportion of fish release, and the release through the square mesh panel was low. But, the results showed that the grid was successful at guiding fish not escaping through the grid to a second selection process in the panel. However, the square mesh panel did not result on the intended release efficiency except for the smallest sizes of fish, most likely because the guiding angle of the grid and the square meshes in the panel used did not provide a suitable escape path for the desired size range of fish. Therefore, optimizing the mesh size/shape in the panel and/or the guiding angle for the grid potentially could lead to the desired selectivity pattern in the new sorting section.

Old-Growth Fishes Become Scarce under Fishing

Researchers have long recognized the importance of ecological differences at the species level in structuring natural communities yet until recently have often overlooked the influence of intraspecific trait variation, which can profoundly alter community dynamics [1]. Human extraction of living resources can reduce intraspecific trait variation by, for example, causing truncation of age and size structure of populations, where numbers of older individuals decline far more with exploitation than younger individuals. Age truncation can negatively affect population and community stability, increasing variability in population and community biomass [2-6], reducing productivity [7-10] and life-history diversity in traits such as the spatial and temporal pattern of reproduction and migration [4, 11-16]. Here, we quantified the extent of age truncation in 63 fished populations across five ocean regions, as measured by how much the proportions of fish in the oldest age groups declined over time. The proportion of individuals in the oldest age classes decreased significantly in 79% to 97% of populations (compared to historical or unfished values, respectively), and the magnitude of decline was greater than 90% in 32% to 41% of populations. The pervasiveness and intensity of age truncation indicates that fishing is likely reducing the stability of many marine communities. Our findings suggest that more emphasis should be given to management measures that reduce the impact of fishing on age truncation, including no-take areas, slot limits that prohibit fishing on all except a narrow range of fish sizes, and rotational harvesting.

Energy Density and Dry Matter Content in Fish: New Observations and an Evaluation of Some Empirical Models

AbstractEnergy density (ED) is an indicator of fish nutritional status, physiological status, and fitness. Estimates of ED of predators and prey are also needed for bioenergetics modeling, but direct measurements of ED are difficult to obtain. Hence, investigators often borrow published values from the same species or related species. Alternatively, models have been developed that predict ED from dry matter content (DM). The scarcity of published ED values makes data borrowing and the generality of predictive modeling difficult to evaluate. We report new ED measurements derived from bomb calorimetry for six freshwater fish species (Arctic Char Salvelinus alpinus, Brown Trout Salmo trutta, kokanee Oncorhynchus nerka, Lake Trout Salvelinus namaycush, Rainbow Trout O. mykiss, and White Sucker Catostomus commersonii) and compared them to previously published data. We used our data to validate existing ED:DM models and to fit new ones. We also quantified bias that could result from borrowing inappropriate ED values for bioenergetics modeling. We collected a range of fish sizes from two reservoirs of differing productivity and measured whole‐body ED (wet‐mass basis) and DM. Our data substantially increase the range of ED data for Arctic Char, kokanee, and White Suckers. Two multispecies ED:DM models predicted the ED of our samples accurately (mean root mean square error [RMSE] < 500 J/g), even at the extremes for the range of prediction where data used for model development were limited. Taxon‐specific models performed less well (mean RMSE = 775 J/g), and some appeared highly biased (RMSE 956−1,900 J/g). Bioenergetics model simulations showed that Lake Trout prey consumption could be overestimated by as much as 22% when using borrowed EDs for Lake Trout and their prey, but prey consumption estimates fell within ±2% of observed when ED was predicted from DM. When direct measures of ED are unattainable, measurement of DM and prediction of ED from one of the published multispecies models offer a practical and accurate method for bioenergetics modeling and other studies requiring information on fish energy content.

Novel aspects of stocked juvenile steelhead emigration patterns as revealed using dual-frequency identification sonar

Abstract We used a Dual-Frequency Identification Sonar (DIDSON) near the mouth of a small Lake Erie tributary to monitor juvenile steelhead emigration. Data were recorded continuously over two stocking seasons (April–May 2014; April–June 2015) and total emigration counts were determined every hour. Fish lengths at time of emigration were estimated using the DIDSON fish measuring tool and quantified through time. Percent survival to emigration was high with > 71% of individuals reaching the river mouth in both years. Photoperiod was the best predictor of peak emigration timing, and steelhead were most likely to emigrate at night. Larger individuals were more likely to emigrate shortly after stocking; however, the size range of fish that emigrated throughout the study period was wide. Residual population estimates performed after the DIDSON sampling period revealed that in both years 2 months after stocking. Most of these fish (63%) were

Basic Methods for the Study of Reproductive Ecology of Fish in Aquaria.

Captive-rearing observations are valuable for revealing aspects of fish behavior and ecology when continuous field investigations are impossible. Here, a series of basic techniques are described to enable observations of the reproductive behavior of a wild-caught gobiid fish, as a model, kept in an aquarium. The method focuses on three steps: collection, transport, and observations of reproductive ecology of a substrate spawner. Essential aspects of live fish collection and transport are (1) preventing injury to the fish, and (2) careful acclimation to the aquarium. Preventing harm through injuries such as scratches or a sudden change of water pressure is imperative when collecting live fish, as any physical damage is likely to negatively affect the survival and later behavior of the fish. Careful acclimation to aquaria decreases the incidence death and mitigates the shock of transport. Observations during captive rearing include (1) the identification of individual fish and (2) monitoring spawned eggs without negative effects to the fish or eggs, thereby enabling detailed investigation of the study species' reproductive ecology. The subcutaneous injection of a visible implant elastomer (VIE) tag is a precise method for the subsequent identification of individual fish, and it can be used with a wide size range of fish, with minimal influence on their survival and behavior. If the study species is a substrate spawner that deposits adhesive eggs, an artificial nest site constructed from polyvinyl chloride (PVC) pipe with the addition of a removable waterproof sheet will facilitate counting and monitoring the eggs, lessening the investigator's influence on the nest-holding and egg-guarding behavior of the fish. Although this basic method entails techniques that are seldom mentioned in detail in research articles, they are fundamental for undertaking experiments that require the captive rearing of a wild fish.

Niche Partitioning in Early Life History Stage, Estuarine-Dependent Fishes (Sciaenidae)

Although the form and function of feeding apparatus structures and diet composition are linked in adult fishes, it is often not clear when during ontogeny ecomorphological patterns develop, enabling early life history stage (ELHS) fishes to partition foraging niches and reduce competition. Species of drums (Sciaenidae) demonstrate tremendous variability in the structure of the feeding apparatus, which allows sympatric species to exploit a broader range of foraging habitats as adults than any other family of fishes in the coastal systems of the western Atlantic. The feeding apparatus (i.e., oral and pharyngeal jaw elements) and stomach contents were examined in ELHS and juvenile sciaenids from the Chesapeake Bay representing three foraging guilds: pelagic, generalist, and benthic. Stomach contents were examined and specimens were cleared and double-stained to measure elements of the feeding apparatus. Regardless of foraging guild, a single diet shift was observed in the size range of fishes examined. Benthic sciaenids were the first to undergo a diet shift at 16 mm SL, which was attributed to changes in the feeding apparatus. Pelagic sciaenids underwent a diet shift at 17 mm SL, which was attributed to a previously studied shift in the sensory modality. The generalist sciaenids were the last to undergo a diet shift at 20 mm SL, which was attributed to changes in both the feeding apparatus and sensory abilities. These ecomorphological patterns identify the developmental events to the feeding apparatus and sensory systems necessary for ELHS sciaenids to begin partitioning their foraging niches, reducing their susceptibility to competition and bottom-up processes in estuarine ecosystems.

Implications of using small meshed gillnets for the sustainability of fish populations: a theoretical exploration based on three case studies

AbstractThe study explores the impacts of varying gillnet mesh size and fishing level on yield per recruit (Y/R), escapement spawning stock (ESS) and mega‐spawners (MS) of three widely distributed freshwater fishery target species. Y/R is maximised when the optimal length of capture (Lcap) is above the size of maturity (L50). However, the unimodal shape of gillnet selectivity results in lower impacts to ESS and MS with both smaller and larger mesh sizes. Under conditions of moderate exploitation, the fraction of MS was significantly larger if small meshed gillnets were used. This is due to the relatively smaller cumulative vulnerability from small mesh sizes through time, as they target a smaller size range of fish, which also grow more quickly through the vulnerable window due to higher growth rates. Therefore, unlike trawls and beach seines, which select all size classes beyond the minimum length of capture (Lc), small meshed gillnets are not necessarily destructive and may rather promote sustained production by allowing a higher proportion of the spawning biomass to remain in the stock. The work also helps to explain the observation of sustained fish production in many developing countries despite the persistent use of gillnets of small mesh size that target small, under‐sized individuals.

Development of a modified cortisol extraction procedure for intermediately sized fish not amenable to whole-body or plasma extraction methods.

The corticosteroid hormone cortisol is the central mediator of the teleost stress response. Therefore, the accurate quantification of cortisol in teleost fishes is a vital tool for addressing fundamental questions about an animal's physiological response to environmental stressors. Conventional steroid extraction methods using plasma or whole-body homogenates, however, are inefficient within an intermediate size range of fish that are too small for phlebotomy and too large for whole-body steroid extractions. To assess the potential effects of hatchery-induced stress on survival of fingerling hatchery-reared Spotted Seatrout (Cynoscion nebulosus), we developed a novel extraction procedure for measuring cortisol in intermediately sized fish (50-100 mm in length) that are not amenable to standard cortisol extraction methods. By excising a standardized portion of the caudal peduncle, this tissue extraction procedure allows for a small portion of a larger fish to be sampled for cortisol, while minimizing the potential interference from lipids that may be extracted using whole-body homogenization procedures. Assay precision was comparable to published plasma and whole-body extraction procedures, and cortisol quantification over a wide range of sample dilutions displayed parallelism versus assay standards. Intra-assay %CV was 8.54%, and average recovery of spiked samples was 102%. Also, tissue cortisol levels quantified using this method increase 30 min after handling stress and are significantly correlated with blood values. We conclude that this modified cortisol extraction procedure provides an excellent alternative to plasma and whole-body extraction procedures for intermediately sized fish, and will facilitate the efficient assessment of cortisol in a variety of situations ranging from basic laboratory research to industrial and field-based environmental health applications.

Using a Laboratory‐Based Growth Model to Estimate Mass‐ and Temperature‐Dependent Growth Parameters across Populations of Juvenile Chinook Salmon

AbstractTo estimate the parameters that govern mass‐ and temperature‐dependent growth, we conducted a meta‐analysis of existing growth data from juvenile Chinook Salmon Oncorhynchus tshawytscha that were fed an ad libitum ration of a pelleted diet. Although the growth of juvenile Chinook Salmon has been well studied, research has focused on a single population, a narrow range of fish sizes, or a narrow range of temperatures. Therefore, we incorporated the Ratkowsky model for temperature‐dependent growth into an allometric growth model; this model was then fitted to growth data from 11 data sources representing nine populations of juvenile Chinook Salmon. The model fit the growth data well, explaining 98% of the variation in final mass. The estimated allometric mass exponent (b) was 0.338 (SE = 0.025), similar to estimates reported for other salmonids. This estimate of b will be particularly useful for estimating mass‐standardized growth rates of juvenile Chinook Salmon. In addition, the lower thermal limit, optimal temperature, and upper thermal limit for growth were estimated to be 1.8°C (SE = 0.63°C), 19.0°C (SE = 0.27°C), and 24.9°C (SE = 0.02°C), respectively. By taking a meta‐analytical approach, we were able to provide a growth model that is applicable across populations of juvenile Chinook Salmon receiving an ad libitum ration of a pelleted diet.Received May 20, 2014; accepted December 4, 2014

Responses of epibenthic and nektonic macroinvertebrate communities to a gradient of fish size in ponds

Size relationships between fish and organisms from adjacent trophic levels are crucial for predicting the structure and dynamics of aquatic ecosystems. We compared macroinvertebrate communities along a fish-size gradient created by separate stocking of three age cohorts of common carp Cyprinus carpio in semi-natural ponds. The specific size range of fish (small, medium and large) corresponding to fish age in ponds was the factor most strongly associated with macroinvertebrate composition. The other significant habitat variables were dissolved oxygen concentration in the water and submerged vegetation abundance in the open-water zone. Among the most numerous taxa in the ponds, relative abundances of Hirudinea, Gastropoda, Odonata and Coleoptera were larger in the presence of small-sized than of larger-sized carp. However, fish size effect was not linear, in that macroinvertebrate assemblages were less similar between ponds containing medium- vs large-sized fish than between ponds with small- vs large-sized fish. The dissimilarity patterns were mainly determined by disparities in abundance of Corixidae, which unlike other taxa common in the ponds occurred in the greatest numbers in the presence of large-sized carp. Macroinvertebrate diversity was greatest in ponds with small-sized fish and was positively related to emergent macrophyte cover. Enhancement of emergent vegetation is recommended as the most effective management strategy to buffer adverse impacts of fish on macroinvertebrates. If fish are present in the system, assessment of the size structure of fish populations can be advantageous in unravelling the essential processes driving the variation in pond communities.

Modelling Size-Dependent Cannibalism in Barramundi Lates calcarifer: Cannibalistic Polyphenism and Its Implication to Aquaculture

This study quantified size-dependent cannibalism in barramundi Lates calcarifer through coupling a range of prey-predator pairs in a different range of fish sizes. Predictive models were developed using morphological traits with the alterative assumption of cannibalistic polyphenism. Predictive models were validated with the data from trials where cannibals were challenged with progressing increments of prey sizes. The experimental observations showed that cannibals of 25–131 mm total length could ingest the conspecific prey of 78–72% cannibal length. In the validation test, all predictive models underestimate the maximum ingestible prey size for cannibals of a similar size range. However, the model based on the maximal mouth width at opening closely matched the empirical observations, suggesting a certain degree of phenotypic plasticity of mouth size among cannibalistic individuals. Mouth size showed allometric growth comparing with body depth, resulting in a decreasing trend on the maximum size of ingestible prey as cannibals grow larger, which in parts explains why cannibalism in barramundi is frequently observed in the early developmental stage. Any barramundi has the potential to become a cannibal when the initial prey size was <50% of the cannibal body length, but fish could never become a cannibal when prey were >58% of their size, suggesting that 50% of size difference can be the threshold to initiate intracohort cannibalism in a barramundi population. Cannibalistic polyphenism was likely to occur in barramundi that had a cannibalistic history. An experienced cannibal would have a greater ability to stretch its mouth size to capture a much larger prey than the models predict. The awareness of cannibalistic polyphenism has important application in fish farming management to reduce cannibalism.

Relation between Nucleic Acid Indices and Growth Rate in Fed and Fasting Juvenile Scup

AbstractThe relationship between nucleic acid indices and daily instantaneous growth rate was determined for juvenile Scup Stenotomus chrysops in the laboratory. Weight‐based growth of Scup was measured for three 1‐week intervals during a 6‐week feeding experiment and showed a significant positive correlation with both RNA concentration (RNA; μg/mg tissue wet weight) and DNA concentration (DNA; μg/mg tissue wet weight), while the RNA: DNA ratio was not significantly correlated with the weight‐ or length‐based growth rate. The concentration of DNA showed a significant negative correlation with length‐based growth rate. Mean fish weight increased from 1.022 to 10.404 g, and mean TL increased from 43.219 to 85.377 mm. Changes in nucleic acid indices were measured in fish that were deprived of food over a 9‐d period. The RNA and RNA: DNA ratio values declined significantly within 5 d after fasting began, while DNA remained relatively stable. This study provides baseline nucleic acid values for fed and starved juvenile Scup over a range of fish sizes.

Influences of a dam on Atlantic salmon (Salmo salar) upstream migration in the Couesnon River (Mont Saint Michel Bay) using hydroacoustics

A dam has been recently modified on the Couesnon River in the vicinity of Mont Saint Michel to control and remove the volume of sediment brought into the bay by tidal waters. This paper shows that this dam has an impact on Atlantic salmon (Salmo salar) migration and that adult fish experience adaptive responses.Upstream migration activities were recorded with a 70 kHz echosounder (SIMRAD EY500 model) during two monitoring programs in 2010 and 2011, combining a total of 172 days of data collection. The echosounder was fixed at an upstream location, 8 km from the dam, and its detection beam capacity was approximately one third of the river's cross sectional area.In addition to the time of year, the upstream direction, swimming speed limit and fish size range were the specific criteria used from our database to efficiently discriminate other fish species from the Atlantic salmon. Among a total of 116,000 fishes counted during the two periods of investigations, 189 salmon were identified using those criteria.This study enabled us to identify the driving factors that influence the salmon migration in this semi-natural environment. There was a significant difference in fish activity when the dam was operating and when the river flow was under “normal” hydraulic conditions.Furthermore, during the opening and closing phases of the dam, the migration activity was scattered during the day, with peak abundance occurring mainly during the beginning of the operating phases. However, during all valve-opening phases, the salmon activity occurred mainly during the night. Therefore, the results suggest that this dam has a strong influence on fish migration activity at this particular location.

Metal concentrations and pathological responses of wild native fish exposed to sewage discharge in a Mediterranean river

The requirements of the Water Framework Directive suggest the need for further research to test and develop sensitive tools that will allow freshwater managers to detect impacts on fish communities. Diagnostic refinement often encompasses the use of lethal diagnostic tools that are incompatible with the conservation of native ichthyofauna. Here we determine the metal concentration and the pathological response of Squalius laietanus exposed to sewage discharges in the Ripoll river (north-eastern Spain), and compare these findings with our previous studies on Barbus meridionalis using lethal and non-lethal diagnostic tools. Metals concentrations (Zn, Cu, Pb, Hg, Fe, Cd and Ni) were determined in liver and muscle. A complete blood cell profile (haematocrit, haemoglobin, differential leukocyte count, erythrocytic nuclear abnormalities, erythrocytes in division and the development stage of erythrocytes) was used as a non-lethal diagnostic tool to determine early warning signs of disease in these two fish species. As the reference range for these haematological variables is lacking, liver histology, calculation of body condition (CF) and organosomatic indices (HSI and GSI) were employed to support the findings of the blood analyses. Compared to our previous results on B. meridionalis, S. laietanus appeared to have fewer pathological responses than B. meridionalis under the environmental conditions measured and the fish size range examined in this study. Both species showed a similar bioaccumulation pattern, but B. meridionalis stored high Hg and Cu concentrations in muscle and liver, respectively. Hg, Cu and Pb concentrations in fish tissues exceeded the thresholds of European and Spanish legislation. Our findings pinpoint the potential suitability of the blood variables determined in the health diagnoses of these species. Further research will be necessary to establish the natural variability of these and other haematological variables to convert haematology into a sensitive and useful non-lethal diagnostic tool in wild fish populations.

Validating Back‐Calculation Models Using Population Data

AbstractOtolith back‐calculation, an estimation of size and growth at some previous age, is a valuable and widely used method of tracking the traits of surviving individuals. Although numerous back‐calculation models have been developed, the accuracy of model prediction is rarely assessed before using a model on wild populations. Using the Atlantic Silverside Menidia menidia, we tested the precision of four commonly used back‐calculation models (body proportional hypothesis, modified Fry, biological intercept, and time‐varying growth). We calculated the moments of the observed length frequency distribution (mean, variance, skewness, and kurtosis) and compared them with the moments of the back‐calculated length frequency distribution predicted by each model. We also compared how the most accurate back‐calculation model changed under various scenarios of size‐selective mortality and found that bias in back‐calculation could not be explained by size‐selective mortality. The differences between functional forms over a wide range of fish sizes were slight for the biological intercept and modified Fry models, whereas the time‐varying growth and body proportional hypothesis models differed considerably. We found that all models performed well for at least one measure of accuracy. However, the modified Fry model was the most accurate overall when back‐calculating to the observed population moments.

Myosin heavy chain and parvalbumin expression in swimming and feeding muscles of centrarchid fishes: The molecular basis of the scaling of contractile properties

In centrarchid fishes, such as bluegill (Lepomis macrochirus, Rafinesque) and largemouth bass (Micropterus salmoides, Lacepède), the contractile properties of feeding and swimming muscles show different scaling patterns. While the maximum shortening velocity (Vmax) and rate of relaxation from tetanus of swimming or myotomal muscle slow with growth, the feeding muscle shows distinctive scaling patterns. Cranial epaxial muscle, which is used to elevate the head during feeding strikes, retains fast contractile properties across a range of fish sizes in both species. In bass, the sternohyoideous muscle, which depresses the floor of the mouth during feeding strikes, shows faster contractile properties with growth. The objective of this study was to determine the molecular basis of these different scaling patterns. We examined the expression of two muscle proteins, myosin heavy chain (MyHC) and parvalbumin (PV), that affect contractile properties. We hypothesized that the relative contribution of slow and fast MyHC isoforms will modulate Vmax in these fishes, while the presence of PV in muscle will enhance rates of muscle relaxation. Myotomal muscle displays an increase in sMyHC expression with growth, in agreement with its physiological properties. Feeding muscles such as epaxial and sternohyoideus show no change or a decrease in sMyHC expression with growth, again as predicted from contractile properties. PV expression in myotomal muscle decreases with growth in both species, as has been seen in other fishes. The feeding muscles again show no change or an increase in PV expression with growth, contributing to faster contractile properties in these fishes. Both MyHC and PV appear to play important roles in modulating muscle contractile properties of swimming and feeding muscles in centrarchid fishes.

Adapting bioenergetic factorial modelling to understand the implications of heat stress on barramundi (Lates calcarifer) growth, feed utilisation and optimal protein and energy requirements - potential strategies for dealing with climate change?

The implications of temperature on bioenergetics for barramundi (Lates calcarifer) were defined in an improved factorial model that encompassed revised parameters accounting for effects over the temperature range of 16–39 °C and size range of 10–3000 g. A revised growth function describing weight gain by barramundi as a function of fish weight and temperature was derived from farm and laboratory data and included a term for a shift in optimal temperature with fish size: Gain (g fish−1 day−1) = (K + xT + yT 2 + zT3) * (weight)ax+b. Maintenance energy and protein demand functions were also derived on a similar form, and all three functions combined to form the basis of a factorial model for energy and protein demand. Using this model, optimal iterative feed specifications were defined for a range of fish sizes at temperatures of 25, 30 and 35 °C. A feed demand model was also developed based on the demand for digestible energy (DE) at each of these temperatures. The model shows that at high temperatures (35 °C), there is an increase in digestible protein (DP) to DE demand, and that with increasing size, there is a decrease in the DP to DE demand.