Size Classes Of Fish Research Articles

Fast, Not Furious - Adaptation of the Species List and Fish Size Classes for Fish Assemblage Survey Technique (FAST) for the Adriatic Sea

Abstract Marine Protected Areas and other managed marine sites are designated to improve the status of coastal fish assemblages and protect valuable habitats. The implementation of management practices relies on data collected through monitoring activities. The monitoring of fish assemblages using the standard non-destructive methods requires significant financial resources and time. A new approach to monitoring fish assemblages in the coastal waters was recently implemented in the Mediterranean – Fish Assemblage Survey Technique (FAST). It is based on Citizen Science where trained volunteer divers collect the data following a pre-established protocol. Considering the differences in species presence/absence and their sizes between the Mediterranean and the Adriatic Sea, a modification of the method was necessary. This study presents 23 main fish species and four ‘joker’ species selected for the Croatian FAST list and their respective sizes that will be considered Large (>2/3 of the total size) for implementing the method in the Croatian part of the Adriatic Sea.

Resource pulses increase the diversity of successful competitors in a multi‐species stream fish assemblage

AbstractFood resources are often patchily distributed through space and time and are classified as resource pulses when hyperabundant. Resource pulses can benefit growth, reproduction, and abundance of various consumers. Yet, it is relatively unknown how such resources are partitioned among competing consumers and how this is influenced by the magnitude of the pulse. Here, we examined how the magnitude of a pulsed resource influences resource partitioning among diverse sizes and species of consumers in a natural setting over small spatial and temporal scales. We focused on salmon egg subsidies to stream fish consumers. We experimentally added different quantities of pink salmon eggs to five meter long experimental stream sections. Egg additions spanned three orders of magnitude from 6 to 3575 eggs. Stream fish (egg consumers) were captured and gastric lavaged at each experimental section to determine how many eggs each individual fish consumed. We modeled taxon‐specific individual egg consumption as a function of egg availability, individual mass, community composition, number of competitors, and stream velocity using hurdle models in a Bayesian framework. We found that there were diminishing returns for increasing egg abundance increasing egg consumption (i.e., type II functional response) for individual size classes of fish, but that higher egg numbers were needed to benefit diverse consumers. Top models indicated that egg availability and individual fish characteristics (size and taxon) drove egg consumption, while community characteristics (species composition and number of competitors) were not supported. Our results suggest that resource pulses can provide rare opportunities for less dominant sizes and species of fish to consume abundant resources. The current paradigm in the stream fish literature suggests that stream fish communities are structured by dominance hierarchies; however, dominance hierarchies may be less influential where pulsed resources comprise a large portion of the resource base.

Feeding habitats of juvenile reef fishes in a tropical mangrove–seagrass continuum along a Malaysian shallow-water coastal lagoon

We conducted stable isotope (δ13C and δ15N) and gut content analyses to understand habitat use of juvenile reef fishes (Lethrinus lentjan, Lutjanus russellii, and Epinephelus coioides), particularly the influence of spatial habitat structure along seagrass–mangrove continua. Sampling was conducted in Setiu Lagoon, located in the southern waters of the South China Sea (Malaysia). Gut content analysis indicated that the focal fishes preyed mainly on benthic invertebrates and other smaller fishes; these were used as potential prey items for isotopic tracers to track fish habitat use. Stable isotope analyses highlighted that the juvenile reef fishes were highly associated with seagrass beds as feeding grounds; however, site-specific analyses suggest differences in fish feeding habitats. The juvenile fishes, particularly large juveniles, preyed in both mangrove and seagrass areas from the central lagoon, whereas all juveniles showed preferential foraging within seagrass meadows in the nearby lagoon mouth. Furthermore, the mean stable isotope values of muscle tissue differed among fish size classes, indicating their ontogenetic habitat/diet shifts, especially for L. lentjan and E. coioides. This study provides important information to support current efforts in protecting and preserving mangroves and seagrasses as crucial nursery habitats for juvenile reef fishes from the anthropogenic activities influencing Setiu Lagoon.

Benzocaine and menthol as anesthetics for the African cichlid Aulonocara nyassae

The objective of this study was to investigate the effects of benzocaine and menthol on the anesthesia of Aulonocara nyassae juveniles. Two size classes of fish were used in trials with benzocaine: Juveniles I—70 fish of 0.74 ± 0.31 g (39.41 ± 7.48 mm); and Juveniles II—70 fish of 3.80 ± 0.92 g (76.58 ± 9.83 mm). The fish used for trials with menthol were as follows: Juveniles I—70 fish of 1.01 ± 0.39 g (50.39 ± 12.75 mm) and Juveniles II—70 fish of 3.73 ± 0.78 g (64.94 ± 8.98 mm). Seven concentrations—0, 12.5, 25.0, 50.0, 75.0, 100.0, and 125.0 mg L−1—of each anesthetic (benzocaine and menthol) were tested on each size class of fish (n = 10 fish per size class and anesthetic concentration). Thus, anesthesia induction time and recovery were evaluated. Concentrations of 12.5 and 25 mg L−1 of benzocaine did not lead to a deep stage of anesthesia in the animals; however, the other concentrations presented anesthetic effect. For menthol, the concentration of 12.5 mg L−1 also did not anesthetize the fish. However, the other doses were effective and safe. The recommended anesthetic concentrations provided induction and recovery times within the limits considered ideal for fish. Concentrations between 75 and 125 mg L−1 of benzocaine for Juvenile I and 50 to 125 mg L−1 for Juvenile II are recommended. For menthol, concentrations between 50 and 125 mg L−1 can be used for both size classes of A. nyassae.

Dome-shaped selectivity in LB-SPR: Length-Based assessment of data-limited inland fish stocks sampled with gillnets

Inland fisheries can support complex social-ecological systems and contribute to food security. However, many target stocks lack monitoring and quantitative assessment. There may be scope to apply current data-limited assessment models in these fisheries. The Length-Based Spawning Potential Ratio (LB-SPR) model requires only fish length data and input estimates of key life history parameters. LB-SPR has been seldom applied in inland systems, partly due to the current model assumption of asymptotic fishing gear selection, characteristic of trawls. In contrast, most inland fisheries operate gillnets or hooks, having dome-shaped selection curves. This is problematic because the largest size classes of fish are not fully retained by the gear, but their absence in the catch will be assumed by the LB-SPR model to reflect fishing mortality. LB-SPR was extended to include dome-shaped selection. Case study assessments were undertaken using survey gillnet catches of brown trout Salmo trutta from four Irish lakes. Bayesian Monte Carlo methods were used to quantify uncertainty around estimates of life history parameters for each stock. Despite small sample sizes, the model produced estimates of SPR that corresponded to expert knowledge of stock status. The extended LB-SPR can be applied to assess data-limited inland fish stocks, and other stocks for which selection is dome-shaped.

Analysis of a coastal North Sea fish community: Comparison of aquatic environmental DNA concentrations to fish catches

AbstractAnalyses of environmental DNA have the potential to become an integrated tool in fish research and management. We performed a pilot study during the spring migration of fishes from the North Sea into the Wadden Sea and present comparative results from daily fyke catches (20 mm mesh) in the Marsdiep tidal inlet on two locations and results from weekly fish eDNA analyses on three locations, all within 2 km distance.Fish catches did not differ significantly between the two locations, whereas the eDNA composition showed a significant location effect. However, when eDNA analysis was restricted to species that were caught with the fykes, differences among locations became insignificant. Over ten weeks, from late April to early July, presence–absence calls of fishes based on weekly eDNA sampling significantly agreed with calls based on seven days of fyke fishing 1 km westwards. Fish eDNA compositions differed significantly among sample days and months but not between tides. Over the season, patterns in eDNA concentration (12S rRNA gene copies/L) inferred from quantitative PCR and Illumina HiSeq community composition corresponded to patterns in wet mass for the eight most abundant fish species in the fyke (>6 weeks present) despite changes in water temperature and changes in fish size class. Small sandeel and gobies, which are important prey for large fishes and birds, were typically missed with the fyke but contributed up to 25%–40% of the fish eDNA depending on the sample location.

Otter diet changes in a reservoir during a severe autumn drought

Abstract Eurasian otters (Lutra lutra) are known to make extensive use of reservoirs in the Iberian Peninsula, where they forage preferentially on small-size fish (10–20 cm). We hypothesized that the usual consumption of small-size fish by otters in reservoirs is not due to prey size preference, but rather to a higher level of difficulty in capturing larger prey. We studied otter diet in a reservoir that experienced an abrupt drop in stored water caused by an unusually severe drought. We compared relative prey size, hunting success, and diving times between the year of the drought (2017) and two standard rainfall years (2015 and 2016). Otters ate a similar proportion of small and large fish during the drought instead of predominantly eating small fish. Mean diving time during the drought was similar to that of the standard climatic years, indicating a similar physiological cost of capture between small and large fish. Otters had higher hunting success in the drought year (89%) than in the standard years (63%) regardless of prey size. This suggests a higher level of catchability of both fish size classes during the drought as the water level was lower. Results suggest that the usual consumption of small-sized fish by otters in reservoirs could not be related to preference or relative abundance but rather to the difficulty of capturing large-size fish when water levels are high.

Over 50 years of fish community monitoring in Illinois’ large rivers: The evolution of methods used by the Illinois Natural History Survey’s Long-term Survey and Assessment of Large-River Fishes in Illinois

This document describes the methodological evolution of the Long-Term Illinois Rivers Fish Population Monitoring Program since its inception. The principal changes include a shift from fixed-site sampling to stratified random sampling at the reach scale to benefit statistical robustness and a concurrent shift from AC electrofishing to pulsed-DC electrofishing to increase the breadth of the diversity and size classes of fishes encountered. These changes in methodology were implemented during the 2016 field season and are based on quantitative assessments of program data and other results from recent peer-reviewed publications. These refinements will likely improve the program’s ability to detect and describe patterns and trends in the fish assemblages of the Illinois River and other large rivers of Illinois and the Midwest.

Assessment of a vertical slot fishway in south‐eastern Australia designed to pass numerous species and size classes of fish

SummaryIn the Barwon River, Australia, a tidal barrage formed a major impediment to fish movement so in 2013 a vertical slot fishway was installed. The assessment of fishways on tidal barriers is rare in Australia so to ensure the fishway was achieving its ecological objective (i.e. successfully passing the target size range of fish of 20–400 mm total length), fish were trapped at the entrance and exit on 12 occasions and the species composition, abundance and length of fish at the two locations were compared. Additionally, a section of the river downstream of the fishway was sampled to ensure fishway trapping accurately reflected the species composition wanting to use the fishway to move upstream. Eighteen species and 69,246 individual fish were caught in the fishway traps. Catch rates between locations did not differ for Common Galaxias (Galaxias maculatus) or Australian Smelt (Retropinna semoni), although species‐specific catch rates were lower at the exit for Flat‐headed Gudgeon (Philypnodon grandiceps), Tupong (Pseudaphritis urvillii) and Yellow‐eye Mullet (Aldrichetta forsteri). Length distribution between locations only differed for Australian Smelt with small fish under‐represented at the exit location (<25 mm total length). Eight species of fish were collected downstream of the fishway that were not collected in it; however, all of these were estuarine dependent except the non‐native Common Carp (Cyprinus carpio). Our results indicate that vertical slot fishways are a suitable design for improving river connectivity at a low head, tidal barrages in south‐eastern Australia. The study reiterates the importance of reinstating connectivity for species with obligate marine/freshwater migratory life history traits, and the indirect benefits of increased productivity made available to upstream areas.

An external tag for fish: tagging effects in different fish size classes and its influence on growth performance and hematology of Lophiosilurus alexandri (Siluriformes: Pseudopimelodidae)

ABSTRACT This study tested an external tag for juveniles of Lophiosilurus alexandri and measured the effects of tagging in different size classes of fishes. Experiment 1 evaluated the retention rate and influence of the tag on survival and growth of three hundred fishes divided Small, Medium and Large size classes. After 90 days of experiment the fishes had 100% survival and the tag had a higher retention rate for animals of the Large size class. Experiment 2 evaluated the tag’s influence on hematology parameters of forty-two fishes at 5, 10 and 30 days post-tagging. In this experiment both tagged and untagged animals experienced 9.4% mortality. The hematocrit was higher on the 30th day for tagged animals than for untagged animals. No difference was observed for leukocytes, plasma protein, erythrocytes and mean corpuscular volume. It was concluded from Experiment 1 that the tag reduced growth performance when applied to small sized juvenile L. alexandri, and that the tag retention rate increased with increasing animal size. Among the hematological parameters studied for juveniles on the Experiment 2 the tag only influenced the hematocrit parameters, which shows that the tag can be used without considerable influence on the hematological parameters of juvenile L. alexandri.

Fish gut content from biological collections as a tool for long-term environmental impact studies

Most of the world’s fish fauna is suffering from different types of human impacts and new conservation tools are required. The fish diet analysis is a tool that has been used to evaluate degradation processes of aquatic environments, however, few long-term studies are performed by several reasons (e.g., lack of funding, opportunity). Our aim was to test whether the fish gut content from biological collections can be used for comparisons with current data and, consequently, be used as a tool for long-term environmental impact studies. We compared the gut content of fish preserved for fifteen years in a biological collection with recently sampled fish, considering the factors size of the specimen, preservation time and preservation form. We did not find differences in the gut content percentage of preservation between fish size classes and preservation time. However, we found differences between preservation form, in which the fish fixed in formalin kept the digestive content preserved while the fish preserved directly in alcohol did not. Thus, we encourage the use of fish gut content from biological collections fixed in formalin for long-term ecological studies. Our findings may help elucidate some long-term effects of human impacts on fish fauna.

Diet and feeding strategy of the forkbeard Phycis phycis (Pisces: Phycidae) from the Portuguese continental coast

The diet and feeding behaviour of the forkbeard Phycis phycis was studied based on 246 stomachs collected between May 2011 and April 2012 from a commercial fleet operating off the central west coast of Portugal. A total of 44 prey items were identified in the stomachs which were merged into major groups to avoid problems with low expected frequencies. The following taxonomic categories were considered: non-decapod Crustacea, Caridea, Anomura, Munida spp., Processa spp., Brachyura, Pisces, Trisopterus luscus. In order to investigate possible diet differences between fish size classes, a cluster analysis was performed using the mean abundance of each prey group by forkbeard 5 cm length class, and three length groups (LG) were obtained: <22.5, 27.5–37.5 and >42.5 cm. Seasonally, Caridea was the main prey group during winter and autumn while Pisces was predominant during the rest of the year. Caridea was the most important prey group for LG1 and LG2 while in LG3 Pisces was the principal one. The forkbeard feeding behaviour may be characterized as presenting a shift pattern from a more generalist diet (small Crustacea, mainly Caridea) in the young adults to a more specialist strategy (teleosts) in the adults.

Trophic pathways supporting Arctic grayling in a small stream on the Arctic Coastal Plain, Alaska

AbstractBeaded streams are prominent across the Arctic Coastal Plain (ACP) of Alaska, yet prey flow and food web dynamics supporting fish inhabiting these streams are poorly understood. Arctic grayling (Thymallus arcticus) are a widely distributed upper‐level consumer on the ACP and migrate into beaded streams to forage during the short 3‐month open‐water season. We investigated energy pathways and key prey resources that support grayling in a representative beaded stream, Crea Creek. We measured terrestrial invertebrates entering the stream from predominant riparian vegetation types, prey types supporting a range of fish size classes, and how riparian plants and fish size influenced foraging habits. We found that riparian plants influenced the quantity of terrestrial invertebrates entering Crea Creek; however, these differences were not reflected in fish diets. Prey type and size ingested varied with grayling size and season. Small grayling (<15 cm fork length (FL)) consumed mostly aquatic invertebrates early in the summer, and terrestrial invertebrates later in summer, while larger fish (>15 cm FL) foraged most heavily on ninespine stickleback (Pungitius pungitius) throughout the summer, indicating that grayling can be insectivorous and piscivorous, depending on size. These findings underscore the potential importance of small streams in Arctic ecosystems as key summer foraging habitats for fish. Understanding trophic pathways supporting stream fishes in these systems will help interpret whether and how petroleum development and climate change may affect energy flow and stream productivity, terrestrial–aquatic linkages and fishes in Arctic ecosystems.

Feeding strategy of silverside species in eutrophic Lake Pátzcuaro, Mexico

The trophic guild, niche breadth, and trophic position of two different ontogenetic phases were measured according to the size of Chirostoma spp. captured in different zones of Lake Pátzcuaro, Mexico. Analyses were carried out at the genus level due the difficulties to find diagnostic characters to separate the three small silverside species accurately, since even the molecular analyses of mitochondrial DNA for a subsample of the most morphologically differentiated specimens were conducted without success. Fish were captured with a seine net during the wet (September and November 2009) and dry (February and June 2010) seasons at four environmentally different sites. Gut contents of 480 Chirostoma specimens were divided into size-class intervals of 38–51 mm and 66–71 mm for analyses. The contribution of each food item was quantified using the frequency of occurrence and area percentage. Fish were categorized by size, and diets were compared between fish sizes and sites. Dorsal muscle tissue and zooplankton were obtained for nitrogen isotope signature (δ15N) analyses. The trophic guild was determined using a modified quadrant method for gut content analysis; the importance of each prey item was estimated according to a modified index of relative importance. Niche breadth was calculated by the Levins’ Index. The trophic position was assessed using the TrophLab Program and stable isotope analysis. The index of relative importance among study sites and fish size classes was determined by a multivariate approach. Silversides represent a secondary and tertiary consumer in Lake Pátzcuaro that feed mainly on evasive prey, such as copepods (55%) and on non-evasive prey, such as cladocerans (25%) at sites with the lowest transparency in the water column (from 350 mm to 150 mm). Fish scales (11%) and insects (6%) were secondary food items. Ingestion of juvenile silversides was rare (1%). Chirostoma spp. prey on insects on the lake bottom and on water hyacinth roots. Based on δ15N analysis, the trophic position of silversides changes between wet and dry seasons. Their opportunistic and specialized predatory feeding strategy indicates the capability of silversides to resist anthropic changes in the lake.

Tradeoffs between fine‐scale site measurements and coarse sensory data for long‐term monitoring of pulsed wetlands

Summary As anthropogenic activities continue to impact ecosystems around the world, the ability to monitor and manage ecosystem health and function increases in importance. Despite this need for monitoring, management projects are often limited by the funding, time and personnel required to gather field data. These costs only increase when considering large dynamic ecosystems, such as pulsed wetlands, that have spatially and temporally variable habitat conditions, thus requiring frequent field measurements across the landscape. The ability to use sensory data can drastically reduce the resources required to monitor field conditions, but can limit the scope and resolution at which data can be measured. Using the Florida Everglades as a model system because of its extensive monitoring and instrumentation network, we compared the effectiveness of large‐scale sensory models of hydrological data with models that incorporate additional fine‐scale habitat variables to account for variations in the dry season densities of small fishes and macroinvertebrates. Since the magnitude of aquatic faunal densities during the dry season greatly affect higher trophic groups, such as wading birds and alligators, the ability to understand the drivers on fish and crayfish densities is of high importance for Everglades restoration and management plans. We found that models using only sensory hydrological variables supported the same hypotheses as models that incorporated additional habitat variables, but the degree of fit was reduced considerably and varied depending on species group. Species more heavily dependent on water for reproduction and survival, such as fish, tended to have better fitting models than species less dependent on water, such as crayfish. Additionally, sensory‐only models were able to detect different responses between size classes of fish to the processes that drive their concentration into drying pools of water, with large fish (>2.5 cm) densities influenced more by landscape structure and small fish (<2.5 cm) densities influenced more by hydroperiod. Our results support the use of sensory data to identify important variables affecting populations for management and restoration efforts. However, the degree to which sensory variables are able to fit species data is dependent upon the ability of sensors to measure major ecosystem drivers and the scale at which sensors can measure environmental change. Although tradeoffs exist between coarse sensory data and finer site‐specific measurements, the benefits of sensory data will increase as the scale of ecosystem management and restoration increases.

Effects of environmental covariates and density on the catchability of fish populations and interpretation of catch per unit effort trends

Quantifying temporal and spatial trends in abundance or relative abundance is required to evaluate effects of harvest and changes in habitat for exploited and endangered fish populations. In many cases, the proportion of the population or stock that is captured (catchability or capture probability) is unknown but is often assumed to be constant over space and time. We used data from a large-scale mark-recapture study to evaluate the extent of spatial and temporal variation, and the effects of fish density, fish size, and environmental covariates, on the capture probability of rainbow trout (Oncorhynchus mykiss) in the Colorado River, AZ. Estimates of capture probability for boat electrofishing varied 5-fold across five reaches, 2.8-fold across the range of fish densities that were encountered, 2.1-fold over 19 trips, and 1.6-fold over five fish size classes. Shoreline angle and turbidity were the best covariates explaining variation in capture probability across reaches and trips. Patterns in capture probability were driven by changes in gear efficiency and spatial aggregation, but the latter was more important. Failure to account for effects of fish density on capture probability when translating a historical catch per unit effort time series into a time series of abundance, led to 2.5-fold underestimation of the maximum extent of variation in abundance over the period of record, and resulted in unreliable estimates of relative change in critical years. Catch per unit effort surveys have utility for monitoring long-term trends in relative abundance, but are too imprecise and potentially biased to evaluate population response to habitat changes or to modest changes in fishing effort.

Comparative water quality and channel catfish production in earthen ponds and a biofloc technology production system

ABSTRACTThis 210-day study compared variation in water quality and fish growth for channel catfish (Ictalurus punctatus; 47 g/fish) stocked in earthen ponds (1.5 fish/m2, 14,820/ha) and in a biofloc technology (BFT) production system with high-density polyethylene-lined rectangular tanks (12.6 fish/m2, 126,000/ha). Feed input and culture environment affected water-quality dynamics. In ponds, phytoplankton uptake predominated and little nitrification occurred, whereas in the BFT system phytoplankton uptake and nitrification maintained low ammonia-nitrogen concentrations. Size classes of fish were skewed toward the larger market sizes in ponds and toward smaller market sizes in the BFT system. Mean final fish weight was 630 g/fish in ponds and 542 g/fish in the BFT system. Despite these differences, fish yield was higher in the BFT system (7.7 kg/m3 v. 1.5 kg/m3) because of the greater initial stocking rate.

For traditional island communities in the Nicobar archipelago, complete no-go areas are the most effective form of marine management

The ability of local communities to sustainably manage natural resource harvests in coral reefs ecosystem depends heavily on the strength of traditional institutions. Coastal communities have evolved a suite of restrictive practices to control marine offtake and there is considerable recent evidence of their effectiveness in protecting and enhancing resource stocks. However, traditionally imposed restrictions can vary considerably in their complexity and in their functional effectiveness. The indigenous communities of the Nicobar Islands are dependent on marine resources for sustenance, managing them with a range of traditionally imposed restrictions. These include limited entry to certain locations, closed seasons and areas, and restrictions on species, size-classes of fish and fishing methods. We tested the relative effectiveness of protection in areas managed under different traditional control regimes by comparing the abundance and biomass of targeted fish groups in managed and unmanaged areas. Our results indicate that reef sites with the strictest form of restriction – essentially no-go areas – had significantly higher abundance and biomass values of most functional groups of fishes compared with partially protected and control locations. In contrast, targeted food fish stocks did not differ from control locations in partially protected sites managed with even complex forms of traditional management. Ensuring that traditional harvest rules are complied is critical to the success of any management system, and our results suggest that they can be most strictly enforced in traditional no-go areas. Our work highlights the importance of critically evaluating the factors influencing traditional management systems to strengthen their ability to protect these reefs from unsustainable overharvest.

Spatial variability in branchial basket meristics and morphology of southern African sardine Sardinops sagax

We examined spatial variability in meristic and morphological characteristics of the branchial basket of sardine Sardinops sagax collected from four geographical regions around the southern African coast, namely Namibia and the South African west, south and east coasts. Our analysis tested the hypothesis of three putative sardine stocks off South Africa, one in each of the three geographical regions. We therefore collected fish data from Namibia to compare with South Africa, because sardine from the two countries are considered to be separate stocks. Morphometric measurements (gill arch length and gill raker spacing) and meristic data (number of gill rakers) were collected from the left side of the first gill arch from a total of 377 sardine, approximately equally divided between the regions. A multivariate general linear model with caudal length as covariate was used to assess differences among fish from the four regions and significant differences were observed, although not always consistently across all fish size classes. Small South Coast sardine had shorter gill arches than small West Coast sardine, but adults had gill arches of similar length, longer than those from Namibia and the East Coast. Small sardine from the South Coast had fewer gill rakers than small sardine from the West Coast, but larger fish had similar numbers of gill rakers, significantly more than sardine from Namibia and the East Coast. Sardine from the West and South coasts had similar gill raker spacings, which were smaller than those of fish from the East Coast and Namibia. Despite spatially and particularly temporally unbalanced sampling, we consider that these differences provide evidence of spatial variation in Benguela sardine phenotype and that it would support the hypothesis of discrete sardine stocks off Namibia and South Africa. The results are consistent with the hypothesis of three sardine stocks within the southern Benguela.

Defining the allometric relationship between size and individual fatty acid turnover in barramundi Lates calcarifer

An experiment was conducted with barramundi (Asian seabass; Lates calcarifer) to examine the allometric scaling effect of individual fatty acids. Six treatment size classes of fish were deprived of food for 21days (Treatment A, 10.5±0.13g; Treatment B, 19.2±0.11g; Treatment C, 28.3±0.05g; Treatment D, 122.4±0.10g; Treatment E, 217.6±0.36g; Treatment F, 443.7±1.48g; mean±SD) with each treatment comprising of fifteen fish, in triplicate. The assessment of somatic losses of whole-body energy and lipid were consistent with previous studies, validating the methodology to be extended to individual fatty acids. Live-weight (LW) exponent values were determined to be 0.817±0.010 for energy and 0.895±0.007 for lipid. There were significant differences among the fatty acids ranging from 0.687±0.005 for 20:5n-3 (eicosapentaenoic acid) and 0.954±0.008 for 18:1n-9 (oleic acid). The LW exponent values were applied to existing fatty acid intake and deposition data of barramundi fed with either 100% fish oil or 100% poultry oil. From this the maintenance requirement for each fatty acid was determined. The metabolic demands for maintenance and growth were then iteratively determined for fish over a range of size classes. Application of these exponent values to varying levels of fatty acid intake demonstrated that the biggest driver in the utilisation of fatty acids in this species is deposition demand and despite their reputed importance, the long-chain polyunsaturated fatty acids had nominal to no maintenance requirement.