Viviparity: The Maternal-Fetal Relationship in Fishes

SYNOPSIS. Viviparity in the vertebrate line first makes itsevolutionary appearance among fishes. It has independently evolvedin a number of divergent piscine lineages. The 54 families ofextant fishes that bear living young include 40 families ofchondrichthyans (sharks and rays), one montypic family of coelacanths(Latimeria), and 13 families of teleosts. There is fossil evidencefor viviparity in holocephalans and chondrosteans. Viviparitypredominates among sharks and rays (40 families, 99 genera,420 species) but is less widespread among teleosts (13 families,122 genera, 510 species). Following an historical introduction,the organization of the female reproductive system, sites ofgestation, developmental sequences and superfetation are considered.The evolution of viviparity establishes specialized maternal-fetalrelationships, viz., 1) developmental, 2) morphological, 3)trophic, 4) osmoregulatory, 5) respiratory, 6) endocrinological,and 7) immunological. While the latter four categories are brieflynoted the major emphasis is on the trophic relationship andits morphological and developmental basis. First, a generaloverview is presented and then the maternal-fetal trophic relationshipsin each of the major groups of fishes are systematically reviewed.Pertinent anatomical, histological, ultrastructural, developmental,physiological, and biochemical studies are considered. Viviparousfishes are either lecithotrophic, i.e., exclusively yolk dependent,or matrotrophic, i.e., in receipt of a continuous supply ofmaternal nutrients during gestation. Nutrient transfer is accomplishedby 1) oophagy and adelphophagy, 2) placental analogues, and3) the yolk sac placenta. Placental analogues include: externalepithelial absorptive surfaces, e.g., skin, fins, gills; trophonemata,modifications of the uterine epithelia for the secretion ofhistotrophe or "uterine milk"; branchial placentae, close appositionbetween gill epithelia and either uterine or ovarian epithelialvilli; the yolk sac; pericardial amnion and chorion; follicularpseudoplacenta, close apposition between follicle cells andembryonic absorptive epithelia; hypertrophied gut; and trophotaeniae,external rosette or ribbon-like projections of the embryonicgut. Among chondrichthyans, the yolk sac placenta (840–1,050%),trophonematal secretion and embryonic absorbtion of histotrophe(1,680–4,900%) and oophagy and adelphophagy (1.2 x 106%)are the most efficient methods of nutrient transfer. Among teleosts,the follicular pseudoplacenta (1,800–3,900%), trophotaeniae(8,400%) and absorption of ovarian histotrophe through surfaceepithelia and a hypertrophied gut (1,100–34,000%) arethe most efficient. These values stand in contrast to the 30%40%loss of dry weight characteristic of oviparous fishes and viviparouslecithotrophes.     

Developmental Data and Phylogenetic Systematics: Evolution of the Vertebrate Limb

Among the primary contributions of phylogenetic systematicsto the synthesis of developmental biology and evolution arephylogenetic hypotheses. Phylogenetic hypotheses are criticalin interpreting the patterns of evolution of developmental genesand processes, as are morphological data. Using a robust phylogeny,the evolutionary history of individual morphological or developmentalfeatures can be traced and ancestral conditions inferred. Multiplecharacters (e.g., morphological and developmental) can be mappedtogether on the phylogeny, and patterns of character associationcan be quantified and tested for correlation. Using the vertebrate forelimb as an example, I show that bymapping accurate morphological data (homologous skeletal elementsof the vertebrate forelimb) onto a phylogeny, an alternativeinterpretation of Hox gene expression emerges. Teleost fishesand tetrapods may share no homologous skeletal elements in theirforelimbs, and thus similarities and differences in Hox patternsduring limb development must be reinterpreted. Specifically,the presence of the phase III Hox pattern in tetrapods may notbe correlated with digits but rather may simply be the normalexpression pattern of a metapterygium in fishes. This exampleillustrates the rigorous hypotheses that can be developed usingmorphological data and phylogenetic methods. "Creating a general reference system and investigating the relationsthat extend from it to all other possible and necessary systemsin biology is the task of systematics." (Hennig, 1966, p.7)     

Motor Control Across Trophic Strategies: Muscle Activity of Biting and Suction Feeding Fishes

Many fishes use a powerful bite of the oral jaws to captureor tear their prey. This behavior has received less study fromfunctional morphologists and physiologists than suction feeding,and presents an opportunity to examine motor control of fishfeeding across alternative prey-capture strategies. We usedelectromyography to compare muscle activity patterns of thefeeding bite in five teleost fishes representing at least threelineages in which biting has been independently acquired: twoparrotfish (Cetoscarus bicolor and Scarus iseri), a wrasse (Cheilinuschlorourus), and two serrasalmines, a pacu (Piaractus brachypomus)and a piranha (Pygocentrus nattereri). Multivariate analysisindicated that muscle activity patterns differed significantlyamong species, although a four-way ANOVA designed to test fordifferences within a phylogenetic hierarchy revealed that thebiting motor pattern was largely similar for both narrow andbroad phylogenetic comparisons. A comparison of the motor patternsof biting and suction feeding species revealed that biters hadsignificantly shorter durations of the epaxialis and sternohyoideusand significantly longer relative onset times of the epaxialis,adductor mandibulae, and sternohyoideus. Character mapping oftiming variables suggested that short relative onset times areprimitive for suction feeders and that this characteristic isgenerally retained in more advanced species. Despite these differences,all species overlap extensively in multivariate EMG space. Ourresults demonstrate that change in the feeding motor patternhas accompanied morphological and behavioral change in transitionsfrom suction to biting, which suggests that the neuromotor systemhas not acted as a constraint on the evolution of the feedingsystem in fishes.     

Constraint and opportunity: the genetic basis and evolution of modularity in the cichlid mandible

Modular variation, whereby the relative degree of connectivity varies within a system, is thought to evolve through a process of selection that favors the integration of certain traits and the decoupling of others. In this way, modularity may facilitate the pace of evolution and determine evolvability. Alternatively, conserved patterns of modularity may act to constrain the rate and direction of evolution by preventing certain functions from evolving. A comprehensive understanding of the potential interplay between these phenomena will require knowledge of the inheritance and the genetic basis of modularity. Here we explore these ideas in the cichlid mandible by investigating patterns of modularity at the clade and species levels and through the introduction of a new approach, the individual level. Specifically, we assessed patterns of covariation in Lake Malawi cichlid species that employ alternate "biting" and "suction-feeding" modes of feeding and in a hybrid cross between these two ecotypes. Across the suction-feeding clade, patterns of modularity were largely conserved and reflected a functionally based pattern. In contrast, the biting species displayed a pattern of modularity that more closely matched developmental modules. The pattern of modularity present in our F2 population was very similar to the pattern exhibited by the biter, suggesting a role for dominant inheritance. We demonstrate that our individual-level metric of modularity (IMM) is a valid quantitative trait that has a nonlinear relationship with shape. IMMs for each model were used as quantitative characters to map quantitative trait loci (QTL) that underlie modularity. Our QTL analysis offers new insights into the genetic basis of modularity in these fishes that may eventually lead to the discovery of the genetic processes that delineate particular modules. In all, our findings suggest that modularity is both a constraining and an evolvable force in cichlid evolution, as distinct patterns occur between species and variation exists among individuals.     

Perspectives on the genetic architecture of divergence in body shape in sticklebacks

The body shape of fishes encompasses a number of morphological traits that are intrinsically linked to functional systems and affect various measures of performance, including swimming, feeding, and avoiding predators. Changes in shape can allow a species to exploit a new ecological niche and can lead to ecological speciation. Body shape results from the integration of morphological, behavioral and physiological traits. It has been well established that functional interdependency among traits plays a large role in constraining the evolution of shape, affecting both the speed and the repeated evolution of particular body shapes. However, it is less clear what role genetic or developmental constraints might play in biasing the rate or direction of the evolution of body shape. Here, we suggest that the threespine stickleback (Gasterosteus aculeatus) is a powerful model system in which to address the extent to which genetic or developmental constraints play a role in the evolution of body shape in fishes. We review the existing data that begins to address these issues in sticklebacks and provide suggestions for future areas of research that will be particularly fruitful for illuminating the mechanisms that contribute to the evolution of body shape in fishes.     

Differential use of zooplankton prey by Ancient murrelets and Cassin's auklets in the Queen Charlotte Islands

The distribution at sea and the food of two similar sized plankton-feedingalcids were examined during the 1981 breeding seasons in thenorthwestern Queen Charlotte Islands, British Columbia. Thetwo alcids, the Ancient murrelet (Synthliboramphus antiquus)and the Cassin's auklet (Prychoramphus aleuticus) have differentchick-rearing strategies. Both species fed predominantly atthe shelf break, although the Cassin's auklet also foraged overseamounts. The feeding distributions of the species appear tobe related to those of their prey. Zooplankton sampling indicatedthat each alcid selects a small and different portion of thezooplankton available in surface waters. The Ancient murrelet'smain foods were euphausiids (Thysanoessa spinifera and Euphausiapacifica) and larval and juvenile fishes. The Cassin's aukletchicks fed chiefly on calanoid copepods (Neocalanus cristatus).euphausiids (mostly Thysanoessa longipes in 1981, but in otheryears also Thysanoessa spinifera), and larval and juvenile fishes.The Cassin's auklets took smaller prey than the Ancient murrelet.Differences in the diets of the two alcid species were associatedwith differences in morphology and chick-rearing strategies.     

Genome Duplications and Accelerated Evolution of Hox Genes and Cluster Architecture in Teleost Fishes

The early origin of four vertebrate Hox gene clusters duringthe evolution of gnathostomes was likely caused by two consecutiveduplications of the entire genome and the subsequent loss ofindividual genes. The presumed conserved and important rolesof these genes in tetrapods during development led to the generalassumption that Hox cluster architecture had remained unchangedsince the last common ancestor of all jawed vertebrates. Butrecent data from teleost fishes reveals that this is not thecase. Here, we present an analysis of the evolution of vertebrateHox genes and clusters, with emphasis on the differences betweenthe Hox A clusters of fish (actinopterygian) and tetrapod (sarcopterygian)lineages. In contrast to the general conservation of genomicarchitecture and gene sequence observed in sarcopterygians,the evolutionary history of actinopterygian Hox clusters likelyincludes an additional (third) genome duplication that initiallyincreased the number of clusters from four to eight. We document,for the first time, higher rates of gene loss and gene sequenceevolution in the Hox genes of fishes compared to those of landvertebrates. These two observations might suggest that two differentmolecular evolutionary strategies exist in the two major vertebratelineages. Preliminary data from the African cichlid fish Oreochromisniloticus compared to those of the pufferfish and zebrafishreveal important differences in Hox cluster architecture amongfishes and, together with genetic mapping data from Medaka,indicate that the third genome duplication was not zebrafish-specific,but probably occurred early in the history of fishes. Each descendingfish lineage that has been characterized so far, distinctivelymodified its Hox cluster architecture through independent secondarylosses. This variation is related to the large body plan differencesobserved among fishes, such as the loss of entire sets of appendagesand ribs in some lineages.     

Special Adaptive Problems Associated with Unisexual Fishes

SYNOPSIS. Two genera of fishes, Poecilia and Poeciliopsis, bothin the family Poeciliidae, have established unisexual populations.One "species," Poecilia formosa, is a diploid form that reliesupon sperm from Poecilia latipinna or P. mexicana to initiateparthenogenetic development (gynogenesis). Triploid individualsof P. formosa have also been discovered but the mode of reproductionand the significance of such fish to natural populations haveyet to be established. In the genus Poeciliopsis three gynogenetic triploids are known.Each is superimposed on a different bisexual host: Poeciliopsislucida, P. monacha or P. viriosa. Five diploid hybridogeneticformsalso have been identified. These are fertilized by either P.lucida, P. latidens, or P. occidentalis. In hybridogenetic forms,sperm actually feitilizes the egg. A hybrid with maternal andpaternal characters is produced, but only maternal genes aretransmitted through the egg to the next generation. Because of their sperm dependency, all unisexual fishes mustreside with at least one of the parental species. They areforcedto compete with them for sperm, space, and other limited resources.The ability to produce two females for every one that bisexualsproduce suggests that the unisexuals have the potential to winthis competition; but in so doing, they would lose their sexualsupport and eliminate themselves. A density-dependent mate selectionsystem plays a role in establishing a workable balance betweenthe competing elements. Unisexual forms of both Poecilia and Poeciliopsis are of hybridorigin. For most of them, the parental precursors and the proportionof genetic material that each contributed to the unisexual isknown. The various genomes that make up the unisexuals are adaptedto a variety of habitats. Once these genomes are combined ina unisexual hybrid, potential for adaptation to multiple nichesexists; this coupled with heterosis contributes greatly to thesuccess of gynogenetic and hybridogenetic fishes.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

Spatial Separation of Ancestral Genomes in the Wild Grass Milium montianum Parl.

Previous work showed a strong tendency for genomes from twodifferent parents to be spatially separated in cell nuclei ofseveral man-made F₁ hybrids between grass species. An importantquestion therefore is whether similar nonrandom genome dispositionoccurs in wild species. Milium montianum Parl. (2n = 22) isa naturally occurring allopolyploid grass combining two geneticallydissimilar chromosome sets (V and M genomes), each originatingfrom a different ancestral species. These two ancestral genomeswere easily discriminated as all V genome chromosomes were largerthan all M genome chromosomes. In two-dimensional spread preparations,the V genome derived from M. vernale Bieb. (2n = 8), and theM genome (of different but uncertain origin) showed a highlysignificant tendency to lie apart. Generally, the V chromosomestended to surround the M chromosomes in both mitotic and meioticnuclei suggesting that this arrangement persists throughoutplant development. Such nuclear organization is probably undergenetic control and may facilitate some independent behaviourof ancestral genomes in allopolyploids. Indeed it may play asignificant role in plant evolution and speciation, especiallyif different intranuclear positions (e.g. central or peripheral)are correlated with preferential phenotypic expression of ancestralgenes. Milium montianum Parl., Gramineae, allopolyploid, spatial chromosome disposition, ancestral genome separation, plant speciation and evolution     

Prehistoric fisheries in the Caribbean

We studied faunal remains from archaeological sites on five Caribbean islands, each with an early (1,850-1,280 years B.P.) and late (1,415-560 years B.P.) occupation. On each of these islands (Puerto Rico, St. Thomas, St. Martin, Saba, and Nevis), the mean size of reef fishes in the faunal remains declined from the early to the late occupation. The large samples from sites on St. Thomas and Nevis allowed examination of the size distribution of individual taxa. Samples of obligate reef fishes (Scaridae, Acanthuridae, Lutjanidae, and Serranidae) showed large reductions in size between the early and late occupations. Samples of facultative reef fishes (Carangidae and Clupeidae) showed little change in size frequency distribution. The percentage of estimated reef fish biomass in the total aquatic faunal record sharply declined in the samples from four of the islands, while on Nevis there was a slight increase. The mean trophic level of reef fishes declined from the early to the late occupations on each island. Together these patterns suggest that populations of reef fishes adjacent to occupation sites on these islands were heavily exploited in prehistoric times. Such exploitation resulted in shifts in size structure and species composition among the reef fish fauna. On some islands the decline in reef fish resources corresponded with a shift towards greater exploitation of pelagic species.     

Chemical Interactions in the Cactus-Microorganism-Drosophila Model System of the Sonoran Desert

The Cactus-Microorganism-Drosophila Model System of the SonoranDesert represents an excellent paradigm of the role of chemistryin plant-animal interactions. In this system, four species ofendemic Drosophila feed and reproduce in necrotic tissue offive species of columnar cacti. Studies over the past 35 yrhave characterized a myriad of interactions between the threemajor components of the model system. The cacti contain a varietyof allelochemicals which are primarily responsible for the highlyspecific pattern of host plant utilization exhibited by thedesert Drosophila. Plant chemistry, through its effect on themicrobially produced volatile patterns, is further involvedin host specificity because the flies use the volatile patternto cue in on necroses in the appropriate species of cactus.The metabolic activities of microorganisms (bacteria and yeasts)living in the necrosis can affect the substrate chemistry inboth positive and negative ways (i.e., acting to increase orto decrease the toxicity of the substrate). Finally, cactuschemistry may affect drosophilid mating behavior since larvalrearing substrate has been shown to influence adult hydrocarbonepicuticular composition. In D. mojavensis, adult hydrocarbonprofile has been implicated as a determinant of mate choiceleading to premating isolation between geographically isolatedpopulations that use chemically different cactus substrates.Current research is focused on the evolution and regulationof genes whose products (cytochrome P450 enzymes) are involvedin the specific insect-host plant relationships which existbetween the Drosophila species and the cactus species. There are many reasons why investigators choose to focus theirresearch efforts on what are referred to as "model systems."Typically included among these would be the idea that modelsystems are easier to study because they are less complex thanother scientific situations. At the same time, model systemsshould be representative of more complex, natural systems sothat information that is obtained from their study is broadlyapplicable. For almost a century, the fruit fly, Drosophilamelanogaster, has served as a model organism for the study ofgenetics. As a genetic paradigm, Drosophila is more tractableto scientific investigation than most organisms and has providedimportant insights into a wide variety of human maladies fromalcohol abuse to neurological brain disorders (Bellen, 1998).Similarly, the interrelationships of the columnar cacti andthe cactophilic Drosophila species of the Sonoran Desert have,for the past 35 yr, provided an excellent model system withwhich to study relevant questions in evolution, ecological genetics,and chemical ecology. The intent of this article is to brieflyreview and characterize the chemical interactions between theplants (cacti) and animals (Drosophila) of this model system,and, in addition, provide some thoughts on possible future directionsfor integrative approaches in this research area.     

Symposium Summary: Evolutionary Patterns in Actinopterygian Fishes

SYNOPSIS. The actinopterygian fishes are an exemplary cladefor the study of structural and functional evolutionary patterns.With over half of all vertebrate species, ray-finned fisheshave diversified into a wide variety of habitats, and considerableprogress has been made over the last fifteen years in understandingthe genealogical relationships of actinopterygians. This symposiumhas contributed to our understanding of phylogenetic patternsin actinopterygians and to knowledge of the major structuraland functional patterns in locomotor, auditory, trophic, andneural systems. A number of key areas for future research havebeen identified. (1) The relationships of "palaeonisciform"fishes, (2) the study of trends in feeding and locomotor systemswithin a phylogenetic context, (3) the identification of primitivepatterns of pharyngeal jaw movement and steady and unsteadylocomotor patterns in actinopterygians, (4) the homologies,identification, and functional significance of neural pathwaysin the telencephalon, and (5) the comparative study of form-functionrelations in the auditory system. The study of teleost fishbiology has proceeded at the expense of data on primitive actinopterygians(e.g., Polypterus, Polyodon, Aapenser, Lepisosteus, Amia) whichare especially important in the analysis of structural and functionalpatterns in ray-finned fishes.     

Behavioral Thermoregulation and the "Final Preferendum" Paradigm

Wider attention to Fry's (1947) "final preferendum" paradigmwould facilitate comparative studies of temperature preference(behavioral thermoregulation) among different animal groups.According to Fry's bipartite definition, the final preferendumis that temperature at which preference and acclimation areequal, and to which an animal in a thermal gradient will finallygravitate regardless of its prior thermal experience (acclimation).This paradigm is helpful in distinguishing between acute thermalpreferenda (measured within 2 hr or less after placing an animalin a thermal gradient), which are influenced by acclimationtemperature, and the species-specific final preferendum (measured24–96 hr after placement in the gradient), which is essentiallyindependent of prior acclimation because reacclimation occursduring the gravitation process. The paradigm does not take intoaccount non-thermal acclimatization influences (e.g., season,photoperiod, age, light intensity, salinity, disease, nutrition,pollutants, biotic interactions) which can also affect temperaturepreference. However, a graph of acutely preferred temperaturesversus acclimation temperatures can be employed to determinean equivalent acclimation temperature for any given acclimatizationstate, as a simple means of quantifying acclimatization statesresulting from interactions of many influences. This paradigm,developed for use with fishes, can also be applied to otherectothermic taxa, although it is most easily employed with aquaticorganisms because of the simplicity of specifying aquatic thermalenvironments in terms of water temperature alone. Methodologiesused in studies of behavioral thermoregulation should take theparadigm into account (especially with respect to length oftests) to enhance the comparative value of data across taxa.     

Structure trees and species trees: what they say about morphological development and evolution

The evolutionary history of morphological structures generally is equated with that of the taxa that carry them. It is argued here that, analogous to genes, developmental genetic pathways underlying morphological structures may be subject to developmental evolutionary changes that result, for instance, in duplication (serial homology analogous to gene duplication and paralogy). Entities that undergo evolution are expected to be related to each other as a tree. Just as with molecular evolution, "structure trees" and species trees sometimes may be incongruent, with implications for morphological homology concepts. Detection of structure trees through morphological evolutionary analyses may point to an entity that is maintained through evolution, possibly in part because it is a developmentally integrated structure ("individualized"). This idea is illustrated in a morphological evolutionary analysis of leaf primordia. These analyses suggest that leaf primordia in monocots and close relatives are related to each other as a tree and, therefore, are developmentally integrated, evolving entities. Among monocot primordia this tree structure breaks down, and it is concluded that there is no entity, the "monocot leaf primordium." However, one group of primordia is identified within monocots that have uniform characteristics and that are well represented by model species maize and rice. Such analyses of structure trees can facilitate the extrapolation and interpretation of results from molecular developmental and other comparative studies.     

Inducible Anisogamy and the Evolution of Oogamy from Isogamy

The initial and decisive step in the evolution of oogamy fromisogamy involves the generation of size different gamete typesin isogamous ancestors. Recent data with isogamous dioeciousChlamydomonas species reveal a potential for the evolution ofanisogamy which can be demonstrated experimentally. These speciespossess, in each sex, two different pathways of gametogenesis.A vegetative cell may produce just one large gamete by intracellulardifferentiation or may produce four small gametes by means oftwo gametogenic mitoses. Combination of sexually complementarygametes of different production modes creates phenotypicallya distinctly anisogamous copulation. At this developmental potential,any mutation which fixes one or the other mode of gametogenesiswill establish micro- or macrogamete producers. Such geneticallyanisogamous lines will then be subjected to selection for increasinglydivergent evolution of the gametic differentiation. Chlamydomonas spp, anisogamy, oogamy, evolution     

Fission in sea anemones: integrative studies of life cycle evolution

Sea anemones (Phylum Cnidaria; Class Anthozoa, Order Actiniaria)exhibit a diversity of developmental patterns that include cloningby fission. Because natural histories of clonal and aclonalsea anemones are quite different, the gain and loss of fissionis an important feature of actiniarian lineages. We have usedmitochondrial DNA and nuclear intron DNA phylogenies to investigatethe evolution of longitudinal fission in sixteen species inthe genus Anthopleura, and reconstructed an aclonal ancestorthat has given rise at least four times to clonal descendents.For A. elegantissima from the northeastern Pacific Ocean, atransition to clonality by fission was associated with an up-shorehabitat shift, supporting prior hypotheses that clonal growthis an adaptation to the upper shore. Fission in Actiniaria likelyprecedes its advent in Anthopleura, and its repeated loss andgain is perplexing. Field studies of the acontiate sea anemoneAiptasia californica provided insight to the mechanisms thatregulate fission: subtidal Aiptasia responded to experimentallydestabilized substrata by increasing rates of pedal laceration.We put forth a general hypothesis for actiniarian fission inwhich sustained tissue stretch (a consequence of substratuminstability or intrinsic behavior) induces tissue degradation,which in turn induces regeneration. The gain and loss of fissionin Anthopleura lineages may only require the gain and loss ofsome form of stretching behavior. In this view, tissue stretchinitiates a cascade of developmental events without requiringcomplex gene regulatory linkages.     

The Development of Fast-Start Performance in Fishes: Escape Kinematics of the Chinook Salmon (Oncorhynchus tshawytscha)

C-starts are high acceleration swimming movements critical forpredator avoidance by fishes. Since larval fishes are particularlyvulnerable to predation, C-start behavior is likely to be especiallyimportant during early life history stages. This paper examinesthe developmental changes in C-start performance with kinematicdata on immature chinook salmon (Oncorhynchus tshawytscha) (eleuthroembryostage, sensu Balon, 1975). The scaling of C-start kinematicsof immature fishes differs from that of adults. Adult C-startdurations increase with increasing body length while C-startdurations of immature fishes decrease (e.g., adult stage 1 duration[sec] = 0.0019.length [L] [cm] $ 0.026 [R² = 0.77] [Webb, 1978];eleuthroembryos stage 1 duration [sec] = –0.026L [cm]$ 0.100 [R² = 0.81]). Distance traveled during stage 2 alsodiffers between adult and immature fishes. Adult distance traveledscales directly with length (distance [cm] = 0.38L^1.01 [cm],R² = 0.96 [Webb, 1978]) while chinook eleuthroembryo distancetraveled is positively allometric with length (distance [cm]=0.37L¹³¹ [cm], R² = 0.83). There are similarities in the developmentof C-starts and burst swimming. For example, mean velocity scalessimilarly between the two locomotor modes (For burst swimming:U_mean [cm/sec] = 8.1 ± 1.1L [cm] $ 4.89 [R² = 0.86] [Webband Corolla, 1981]. For C-start stage 2: U_mean [cm/sec] = 10.96L[cm] - 14.09 [R² = 0.70]). This study demonstrates that C-startescape performance improves during early post-hatching development.Comparisons of immature chinook salmon fast-starts with dataon larval burst swimming and on adult C-starts suggest thatchanges specific to developing fish affect the scaling of kinematicparameters.