Gills,growth and activity across fishes

Life history theory suggests that maximum size and growth evolve to maximize fitness. In contrast, the Gill Oxygen Limitation Theory (GOLT) suggests that growth and maximum size in fishes and other aquatic, water-breathing organisms is constrained by the body mass-scaling of gill surface area. Here, we use new data and a novel phylogenetic Bayesian multilevel modelling framework to test this idea by asking the three questions posed by the GOLT regarding maximum size, growth and gills. Across fishes, we ask whether the body mass-scaling of gill surface area explains (1) variation in the von Bertalanffy growth coefficient (k) above and beyond that explained by asymptomatic size (W_∞), (2) variation in growth performance (a trait that integrates the tradeoff between k and W_∞) and (3) more variation in growth performance compared to activity (as approximated by caudal fin aspect ratio). Overall, we find that there is only a weak relationship among maximum size, growth and gill surface area across species. Indeed, the body mass-scaling of gill surface area does not explain much variation in k (especially for those species that reach the same W_∞) or growth performance. Activity explained three to five times more variation in growth performance compared to gill surface area. Our results suggest that in fishes, gill surface area is not the only factor that explains variation in maximum size and growth, and that other covariates (e.g. activity) are likely important in understanding how growth, maximum size and other life history traits vary across species.     

Gill morphometry of the facultative air-breathing loricariid fish,Hypostomus plecostomus (Walbaum) with,special emphasis on aquatic respiration

Gill respiratory surface area and oxygen consumption during aquatic respiration were measured in the facultative air-breathing loricariid fish,Hypostomus plecostomus. The fish did not surface to breathe atmospheric air in normoxic water; air-breathing was evoked by environmental hypoxia (water oxygen tension=35±2, mmHg) and did not show size-related threshold differences for air breathing.During gradual hypoxia, without access to atmospheric, air,H. plecostomus was found to be an oxyregulator and showed a reduced range of water oxygen tension in which the oxygen consumption remained constant in smaller fish. The critical oxygen tensions were 55 and 33 mmHg at 25°C for fish of 14–30 g and 31–80g body weight, respectively.The gill respiratory surface area (total lamellae area) is reduced, however, the lamellar frequency per mm of gill filament is high which facilitates the gas exchange. Moreover, the increase of gill respiratory surface area (b=0.666) is higher than the increase in routine VO₂ (b=0.338) showing a positive relationship between the gill respiratory surface area /VO₂ ratio and body mass (b=0.328); this indicates that the fish have greater gill respiratory surface area per unit of routine VO₂ as they grow.     

Gill development in sympatric morphs of Arctic charr from Loch Awe,Scotland: A hidden physiological cost of macrobenthos feeding?

The development of the respiratory surfaces was compared in two sympatric, lacustrine morphs of Arctic charr. A macrobenthic invertebrate feeding specialist, that forages in the littoral benthic zone, had a gill cavity that was 54% larger in volume and had 31% greater respiratory surface area than that of a zooplankton feeding morph that forages in the pelagic zone. The large respiratory surface area in the benthic‐feeding form was the result of longer gill arches, more and longer gill filaments and more numerous secondary lamellae. The difference in gill cavity volume and filament length appears to be the result of a larger head, but not body size, in the benthic‐feeding form. This suggests that differences in these characteristics may have arisen as a by‐product of the expression of larger head size commonly described in macrobenthos foraging specialist charr. The other differences, particularly the more numerous secondary lamellae and the length of the gill arches, were not the result of head size differences between morphs, and thus, these are most likely an adaptation to greater respiratory requirements. Benthic‐feeding fish may have a greater respiratory capacity to allow them to forage in areas with lower levels of dissolved oxygen and/or engage in a more active lifestyle compared to the pelagic‐feeding form. In any event, the strikingly larger respiratory surface is likely to impose an additional ionoregulatory stress on the benthic‐feeding and thus may represent a hidden physiological cost of specialisation for foraging on benthic prey.     

Gill morphometry of the red drum,Sciaenops ocellatus

The structure and morphometry of the gills of the marine teleost, red drum, have been studied. The present analysis of gas exchange area of fish gills is one of the most intensive and the results are compared to less intense averaging methods. Based on the gill area estimates, red drum falls into the category of a fish of intermediate activity. Its gill clearly has an exchange area less than that of the tunas, but is slightly greater than that of trout or bass. The three components that contribute to total exchange area (filament length, lamellar density, and area of individual lamellae) are not all greater in species with a greater total exchange area. The best correlate is total filament length.     

Simulation of the effects of oxygen on food consumption and growth of Nile tilapia, Oreochromis niloticus (L.)

Fish need oxygen for aerobic generation of energy for body maintenance, locomotion, feeding and biosynthesis. The rate of oxygen uptake of most fish is limited by diffusion through the gills, and gill surface area grows at a slower rate than body mass. We hypothesize, therefore: (1) that the maximum rate of feed intake is related to the capacity to take in oxygen for processing of this feed; and (2) that the maximum rate of feed intake relative to body size decreases with increasing body size to a point where growth is zero. An oxygen limitation module based on this theory was incorporated into an existing dynamic simulation model for the Nile tilapia, Oreochromis niloticus (L.). The module calculates the maximum potential oxygen supply to the fish on the basis of Fick's law of diffusion and the allometric relationship between body weight and gill surface area. Total oxygen demand of the fish is computed as the sum of routine metabolism, feeding metabolism and energy needed for biosynthesis. In the module, the feeding rate is limited to a level where total oxygen demand does not exceed the potential supply. The model is used to simulate feeding and growth of O. niloticus. Simulation results provide strong support for the oxygen limitation theory. Hence, the model can be used for the analysis of fish growth as affected by feed amount, feed composition, as well as environmental conditions (temperature, dissolved oxygen concentration). It also explains differences in final size between fish species, and within species under different conditions.     

缢蛏鳃的光镜与扫描电镜研究

用光镜和扫描电镜观察了缢蛏鳃的组织学和表面结构。鳃丝有主鳃丝和普通鳃丝之分,鳃丝表面有前纤毛和侧纤毛,分别与食物的运送和呼吸水流的产生有关。普通鳃丝的扁平细胞为呼吸上皮。相邻鳃丝通过含有血管的丝间连接连系,相邻的鳃小瓣通过隔膜状的瓣间连接连系。两根主鳃丝之间的12~22根鳃丝由簇内连接连接成簇。     

扁玉螺鳃的形态学研究

用光镜和扫描电镜观察了扁玉螺鳃的组织学和表面结构,鳃叶上皮由５个区带的细胞组成,即前纤毛柱状细胞,立方细胞,侧纤毛柱状细胞,后纤毛柱状细胞及呼吸上皮。侧纤毛是产生呼吸水流的动力来源,呼吸上皮细胞表面凹凸不平,其组织学和表面结构有助于进行气体交换。     

Gill net selectivity for perch (Perca fluviatilis) in the Szczecin Lagoon, Poland

This paper presents the scientific basis for changes in the minimum mesh size in gill nets, from 28 to 30 mm, introduced by fishery management in Poland to limit the catch of undersized perch (those less than 17 cm total length). Experimental fishing with six different mesh sizes was performed in accordance with commercial fisheries practice. A bi-normal selection curve was fitted to the data by including the between-set variation in the model. The locations of the primary and secondary modes of the bi-normal curve on the transformed length scale (length/mesh) were estimated to be 6.95 and 7.41, respectively. The results indicated that a minimum mesh size in gill nets of 28 mm should be sufficient to ensure a low level of discards as well as protecting the interests of fishermen.     

What determines the size of teleost erythrocytes? Correlations with oxygen transport and nuclear volume

An inverse relationship exists between erythrocyte size and the aerobic swimming ability of teleosts. A functional basis for this relationship is found in larger surface area to volume ratios and shorter diffusion distances allowing more rapid oxygen transfer as erythrocyte volume decreases. However, this apparently simple functional relationship is confounded by a more general direct relationship between cell size and nuclear volume. Nuclear DNA content, which is directly proportional to nuclear volume, is known to vary at least 11 fold among teleost species. Therefore a question arises as to the relative contributions of nuclear volume and the demands of the blood oxygen delivery system in determining erythrocyte volume.These relationships were investigated by regressing erythrocyte volume against nuclear volume and whole blood haemoglobin concentration (as an index of aerobic scope) for 52 species of teleost fish from 25 families. This analysis shows that erythrocyte volume is more highly correlated with oxygen delivery than with nuclear volume. However, much of the variation in erythrocyte volume is unexplained.     

Temperature effects on hatching and viability of Juvenile Gill Lice,Salmincola californiensis

Salmonids of the genus Oncorhynchus, distributed throughout the Pacific Rim, can be infected by the gill lice species Salmincola californiensis (Dana, 1852), which makes them one of the most broadly distributed gill lice species. Despite their broad distribution and valuable obligate salmonid hosts, relatively little is known about S. californiensis. We evaluated effects of temperature on timing of S. californiensis hatching and survival of copepodids, and provide information on brood size and variability. Our results suggest that temperature was a primary driver of timing of S. californiensis hatching and post‐hatching survival. Prior to this study, the free‐swimming stage of S. californiensis was reported to survive approximately 2 days without a suitable host. We observed active copepodids 13 days after hatch with some individuals from most (>90%) viable egg sacs at all temperature treatments surviving ≥5 days. Our findings indicate that warmer temperatures could increase development rates of gill lice at certain life stages, potentially increasing fecundity. This information coupled with predictions that warmer water temperatures could intensify crowding of coldwater fishes, stress, and parasite transmission suggests that climate change could exacerbate negative effects of S. californiensis on ecologically and economically important salmonids.     

Variability in the performance of juvenile Chinook salmon is explained primarily by when and where they resided in estuarine habitats

Estuarine habitats provide rearing opportunities for the juvenile life stage of anadromous fishes. Because survival is positively correlated with juvenile performance, these estuarine habitats play an important role in population abundance and productivity. To provide information for the recovery of several depressed stocks of Chinook salmon in the Columbia River Basin, we sought to identify the factors that explain variability in performance. Using otolith‐derived estimates of juvenile somatic growth rate as an index of recent performance, we observed a negative nonlinear relationship between growth rate and day of year, and a decreasing and increasing trend of growth rate over the 8 years of this study and distance from the river mouth respectively. Using a generalised linear modelling approach, we found that variability in juvenile somatic growth rate was best explained by where and when individuals were collected, their body size, contaminant loads, stock of origin, and whether a fish was hatchery produced or unmarked. Lastly, we argue that a considerable improvement to the growth rate of juveniles in estuarine habitats is physiologically possible. The results of this 8‐year study provide a baseline of the performance of juvenile Chinook salmon to evaluate habitat restoration programs and to compare against future anthropogenic conditions.     

Environmental correlates of body size distribution in Cyprinidae (Actinopterygians) depend on phylogenetic scale

The pattern of increasing species body size with increasing latitude has been noticed in different groups of animals. Here, we used seven key environmental factors and independent contrasts to assess body size latitudinal clines in Cyprinidae at two phylogenetic levels (inter‐ and intragenera), which were defined using a genus‐level supertree. Model selection procedures revealed that environmental factors shaping body size variation in Cyprinidae differed according to the phylogenetic scale considered. At the higher phylogenetic level, we found that both temperature (negative effect) and habitat availability (positive effect of drainage basin surface area) constituted mechanistic explanations of large‐scale body size distribution. No temperature‐related body size cline was observed at the intragenus level. Instead, competitive interaction (negative effect of species richness), habitat availability (positive effect of drainage basin surface area), migration ability and available energy (positive effects of glacial coverage and actual evapotranspiration) constitute alternative explanations at this lower phylogenetic scale. We conclude that (i) at the intergenus level, cyprinids do show a tendency to be smaller at high temperatures and larger at low temperatures, (ii) this tendency no longer exists at the intragenus level, (iii) latitude per se is a weak predictor of body size clines whatever the taxonomic level analysed, (iv) generalising geographical body size patterns may be rendered difficult by the superimposition of a series of mechanisms across different taxonomic scales, and (v) habitat size, here acting positively at both taxonomic scales, may play a major role in shaping riverine species body size clines.     

Rainbow trout gill epithelial cells in primary culture communicate through gap junctions as demonstrated by dye-coupling

Communication across gap junctions between cells in various tissues is considered an important mechanism for control of cellular growth, differentiation and function. Although cell-cell coupling in the gill epithelium is likely for functional reasons, the common view is that gap junctions are not present between cells in the gill epithelium of teleostean fish. Gap junction mediated cell-cell communication was analysed in the present study in primary and secondary cultures of rainbow trout gill epithelial cells by microinjecting the fluorescent dye Lucifer yellow CH. In 4–14 day-old primary and secondary cell cultures, 58% of the cells injected with Lucifer yellow were coupled to at least one other cell. To exclude the possibility that intercellular dye transfer occurred through cytoplasmic bridges instead of gap junctions, we also microinjected FITC-dextran, which because of its molecular size does not pass through gap junctions. None of the cells injected with FITC-dextran showed spreading of the dye. The number of cells spreading Lucifer yellow was decreased in a dose-dependent way when the cells were treated with dioctanoylglycerol, a synthetic diacylglycerol known to affect the open state of gap junctions, which further supports that the cells are coupled through functional gap junctions.     

Predation as a determinant of size structure in populations of crucian carp (Carassius carassius) and tench (Tinea tinea)

Predation is an important structuring force in many fish assemblages and may have large, direct lethal effects on prey fish populations but also may affect growth rate and survival indirectly through shifts in behavioral patterns. Some species appear more sensitive to predation and earlier studies in a limited set of Finnish ponds suggests that crucian carp (Carassius carassius) is very sensitive to predation, which results in changes in population size-structure and density. In this study we tested the effect of piscivore presence or absence on crucian carp populations by using data from a large number (>600) of Swedish lakes across a wide geographical area and ranging in size from small ponds to large lakes (0.02–4400 ha). We also included a second species, tench (Tinea tinea), in our analyses. The population size structures of crucian carp and tench were clearly related to the presence or absence of piscivores. In lakes and ponds without piscivores. populations were dominated by small-bodied individuals. When piscivores were present, populations consisted almost exclusively of large individuals. Densities of crucian carp and tench were much higher in ponds and lakes without piscivores. There were no differences in size structure or relative abundance when catches from electrofishing were compared with gill net catches, suggesting that our results are not an effect of a behavioral shift in the presence of piscivores.     

Variation in characteristics among gizzard shad populations: The role of impoundment size and productivity

Population characteristics of gizzard shad, Dorosoma cepedianum (Lesueur), an ecologically important fish species in Midwestern and southern USA impoundments, vary widely among water bodies. Impoundment productivity is known to influence population variables (e.g., recruitment, growth, mortality, size and age composition), but the role of impoundment morphometry (e.g., surface area, depth) is unknown. Differences in population characteristics of gizzard shad were compared between large and small impoundments across an impoundment–productivity gradient (indexed by total phosphorus [TP] concentration). Populations shifted from those comprised mostly of low abundances (indexed by catch per unit effort [CPUE], fish/hr of electric fishing) of long‐lived, large adults to those comprised of high abundances of short‐lived, small adults as TP increased. However, the trends in population variables across the TP gradient were less apparent in small impoundments than in large impoundments owing to considerable variation at a given TP level. Further analysis revealed that CPUE of gizzard shad was lowest in the smallest impoundments (<33 ha surface area) regardless of TP concentrations, probably because of more frequent winter kills. Overall, population characteristics were influenced by both density‐dependent effects and impoundment characteristics. Characteristics of gizzard shad were highly variable among populations, which have important consequences for ecosystem structure and function.     

Larval and juvenile Australian smelt Retropinna semoni somatic and otolith growth parameters – implications for growth interpretation of wild fish

Abstract –  Relationships between fish length, otolith size, age and weight were assessed for a population of wild Australian smelt ( Retropinna semoni ) larvae and juveniles captured over a 4-year period to aid further interpretation of growth and condition during the early life history of the species. Nonlinear smoothed generalized additive models best described the fish–otolith size relationship during the larval and juvenile period, indicating that the proportionality between fish length and otolith size varies in relation to size. It is proposed that back-calculated predictions of fish size at a previous age or otolith size, accounting for individual variation is possible by assuming a body proportional hypothesis. Growth rate of larval and juvenile Australian smelt was best described using the Gompertz model that indicated a steady decline in growth rate after around 30 days of age. The allometric growth of larval and juvenile Australian smelt established from the length/weight relationship can subsequently be used to assess the condition of fish within this population using a relative condition or relative weight condition index. The results of the study have provided significant information to enable more precise growth reconstruction and condition assessment for the species in Australian lowland rivers.     

Interrelationships between gill chloride cell morphology and calcium uptake in freshwater teleosts

The involvement of the freshwater fish gill chloride cells (CCs) in trans-branchial calcium uptake (JinCa²⁺) was investigated. This was accomplished by assessing the interspecific relationships between the apical surface area of CCs exposed to the external environment and JinCa²⁺. Three species of freshwater teleosts, the rainbow trout (Oncorhynchus mykiss), the American eel (Anguilla rostrata) and the brown bullhead catfish (Ictalurus nebulosus), were used. Chronic (ten-day) treatment with cortisol in each species was used as a tool to evoke variations in both JinCa²⁺ and gill CC morphology in order to assess intraspecific relationships between CC surface area and JinCa²⁺. The results of quantitative morphometry, based on analysis of scanning electron micrographs, demonstrated that catfish possessed the lowest fractional area of exposed CC (CCFA) on the gill filament epithelium (12,744 ± 2248 m²/mm²) and was followed, in increasing order, by American eel (21,355 ± 981 m²/mm²) and rainbow trout (149,928 ± 26,545 m²/mm²). With the exception of catfish, chronic treatment with cortisol caused significant increases in CCFA owing to proliferation of CCs and/or enlargement of individual CCs (eel only). The rates of JinCa²⁺ closely reflected the CC fractional area in each species. The results of correlation analysis revealed significant correlations between CC fractional area and JinCa²⁺ in trout and eel. Owing to the absence of an effect of cortisol treatment, there was no significant correlation in catfish because of insufficient variation in CC fractional area in this species. CC fractional area was significantly correlated with JinCa²⁺ among the three species examined. These results suggest that CC is involved in calcium uptake in freshwater teleosts and that both intra- and interspecific differences in the rates of calcium uptake can be accounted for by variability in the surface area of exposed CCs on the gill epithelia.     

鲤鱼鳃组织结构及鳃对重金属离子的耐受性

采用不同浓度的重金属对鲤鱼进行不同时间的中毒试验，构成了鳃组织的耐量试验。试验表明，当超过鳃的耐受量时，鳃发生了不同阶段的病变。在低浓度短时间作用下，鳃组织分泌的粘液增多。随着浓度的增加和时间的延长，鳃组织出现鳃血管扩充、充血，呼吸上皮肿胀，鳃小片呈棍棒状，相邻几条鳃丝发生融合，形成一片细胞板。有些鳃细胞脱离。病状严重时造成鳃小片坏死、解体导致鳃功能的损害和破坏。     

卵形鲳鲹胚后发育阶段鳃的分化和发育

采用组织学和扫描电镜等方法,鲹研究了卵形鲳(Trachinotus ovatus)胚后发育阶段鳃的分化和发育及其结构和功能的关系。观察发现,仔稚鱼鳃的早期发育可分为3个阶段:第1阶段(0~3日龄)为原基期,鳃原基形成但未分化,鳃耙未出现,仔鱼主要依靠鳍褶、皮肤和卵黄囊上的微血管进行呼吸;第2阶段(4~17日龄)为鳃丝分化、发育期,鳃弓、鳃丝、鳃小片、鳃耙逐渐形成,具备鳃的基本结构和形态特点;第3阶段(18日龄之后)为鳃器官生长发育完善期,鳃弓、鳃丝、鳃小片、鳃耙发育完善,鳃的形态和功能与成鱼相似。进一步研究发现,鳃丝总数随仔稚鱼全长和体质量的增加而增加,单个鳃小片面积和总呼吸面积随仔稚鱼体质量的增加而增大。结果表明,卵形鲳鲳鲹的分化和发育是与仔、稚鱼的生长、形态发育和功能的完善相一致的。     

Evidence for genetic distinction among sympatric ecotypes of Arctic char (Salvelinus alpinus) in south‐western Alaskan lakes

Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south‐western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise F_ST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’‐, ‘medium’‐, and ‘small’‐bodied char; maximum F_ST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = ?0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char.