Growth during the early life history of the Pacific tarpon,Megalops cyprinoides

The early growth of the Pacific tarpon,Megalops cyprinoides, was studied by larval otolith analysis and rearing of larvae and juveniles in the laboratory. Morphology of the sagitta, validation of sagittal daily increments, age at the start of metamorphosis, decrement of standard length in early metamorphosis, and growth under rearing conditions are described. The sagitta of fully-grown Pacific tarpon leptocephali were transparent and circular, with regular intervals between the neighboring rings becoming wider at the onset of metamorphosis. Alizarin complexone treatment of larvae confirmed the daily formation of the sagittal rings. Metamorphosis was estimated to start about one month after hatching. After drastic shrinkage during the first several days of metamorphosis, the body length more or less stabilized for one month and then resumed rapid growth. The early growth of Pacific tarpon was divided into four phases as follows: A) leptocephalus positive growth phase; B) leptocephalus negative growth phase; C) sluggish growth phase; and D) juvenile growth phase.     

Air breathing minimizes post-exercise lactate load in the tropical Pacific tarpon, Megalops cyprinoides Broussonet 1782 but oxygen debt is repaid by aquatic breathing

Swimming in a flume at reduced water pO₂ resulted in muscle and blood lactate levels in Pacific tarpon Megalops cyprinoides that were significantly higher when fish did not have access to air. Blood glucose and haematological variables were unchanged throughout the regimes of exercise at two swimming speeds and hypoxia. Strenuous exercise with bouts of burst swimming, however, resulted in both high blood lactate and glucose, and perturbed haematological status with elevated haemoglobin and reduced mean cell-haemoglobin concentration. Post-exercise recovery was achieved through aquatic breathing rather than by air breathing. The air-breathing organ in Pacific tarpon therefore prolonged aerobic activity, but gill breathing was used to repay oxygen debt.     

Continuous measurement of oxygen tensions in the air-breathing organ of Pacific tarpon (Megalops cyprinoides) in relation to aquatic hypoxia and exercise

The Pacific tarpon is an elopomorph teleost fish with an air-breathing organ (ABO) derived from a physostomous gas bladder. Oxygen partial pressure (PO₂) in the ABO was measured on juveniles (238 g) with fiber-optic sensors during exposure to selected aquatic PO₂ and swimming speeds. At slow speed (0.65 BL s⁻¹), progressive aquatic hypoxia triggered the first breath at a mean PO₂ of 8.3 kPa. Below this, opercular movements declined sharply and visibly ceased in most fish below 6 kPa. At aquatic PO₂ of 6.1 kPa and swimming slowly, mean air-breathing frequency was 0.73 min⁻¹, ABO PO₂ was 10.9 kPa, breath volume was 23.8 ml kg⁻¹, rate of oxygen uptake from the ABO was 1.19 ml kg⁻¹ min⁻¹, and oxygen uptake per breath was 2.32 ml kg⁻¹. At the fastest experimental speed (2.4 BL s⁻¹) at 6.1 kPa, ABO oxygen uptake increased to about 1.90 ml kg⁻¹ min⁻¹, through a variable combination of breathing frequency and oxygen uptake per breath. In normoxic water, tarpon rarely breathed air and apparently closed down ABO perfusion, indicated by a drop in ABO oxygen uptake rate to about 1% of that in hypoxic water. This occurred at a wide range of ABO PO₂ (1.7–26.4 kPa), suggesting that oxygen level in the ABO was not regulated by intrinsic receptors.     

Partitioning of respiration between the gills and air-breathing organ in response to aquatic hypoxia and exercise in the pacific tarpon, Megalops cyprinoides

The evolution of air-breathing organs (ABOs) is associated not only with hypoxic environments but also with activity. This investigation examines the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon. The two-species cosmopolitan genus Megalops is unique among teleosts in using swim bladder ABOs in the pelagic marine environment. Small fish (58-620 g) were swum at two sustainable speeds in a circulating flume respirometer in which dissolved oxygen was controlled. For fish swimming at 0.11 m s(-1) in normoxia (Po2 = 21 kPa), there was practically no air breathing, and gill oxygen uptake was 1.53 mL kg(-0.67) min(-1). Air breathing occurred at 0.5 breaths min(-1) in hypoxia (8 kPa) at this speed, when the gills and ABOs accounted for 0.71 and 0.57 mL kg(-0.67) min(-1), respectively. At 0.22 m s(-1) in normoxia, breathing occurred at 0.1 breaths min(-1), and gill and ABO oxygen uptake were 2.08 and 0.08 mL kg(-0.67) min(-1), respectively. In hypoxia and 0.22 m s(-1), breathing increased to 0.6 breaths min(-1), and gill and ABO oxygen uptake were 1.39 and 1.28 mL kg(-0.67) min(-1), respectively. Aquatic hypoxia was therefore the primary stimulus for air breathing under the limited conditions of this study, but exercise augmented oxygen uptake by the ABOs, particularly in hypoxic water.     

Separating the effects of prey size and speed on the kinematics of prey capture in the omnivorous lizard Gerrhosaurus major

Feeding behavior is known to be modulated as prey properties change. During prey capture, external prey properties, including size and mobility, are likely some of the most important components in predator–prey interactions. Whereas prey size has been demonstrated to elicit modulation of jaw movements during capture, how prey speed affects the approach and capture of prey remains unknown. We quantified the kinematics associated with movements of both the feeding and locomotor systems during prey capture in a lizard, Gerrhosaurus major, while facing prey differing in size and mobility (newborn mice, grasshoppers, and mealworms). Our data show that the feeding and locomotor systems were recruited differently in response to changes in the size or speed of the prey. The timing of jaw movements and of the positioning of the head are affected by changes in prey size—and speed, to a lesser extent. Changes in prey speed resulted in concomitant changes in the speed of strike and an early and greater elevation of the neck. External prey properties, and prey mobility in particular, are relevant in predator–prey interactions and elicit specific responses in different functional systems.     

Modulation and variability of prey capture kinematics in clariid catfishes

Species with narrow or limited diets (trophic specialists) are expected to be less flexible in their feeding repertoire compared to species feeding on a wide range of different prey (trophic generalists). The ability to modulate prey capture kinematics in response to different prey types and prey position, as well as the overall variability in prey capture kinematics, is evaluated in four clariid species ranging from trophic generalist (Clarias gariepinus) to species with morphological specializations and a narrow diet (Channallabes apus and Gymnallabes typus). High-speed video recordings were made of prey captures on two prey that differ in shape, attachment strength and hardness. While the observed amount of strike-to-strike variability in prey capture kinematics is similar for all species and not influenced by prey type, only the two less specialized species showed the ability to modulate their prey capture kinematics in function of the presented prey types. All species did, however, show positional modulation during the strike by adjusting the magnitude of neurocranial elevation. These results indicate that the narrow dietary breadth of trophic specialists is indeed indicative of functional stereotypy in this group of fishes. Although most studies focussing on prey processing found a similar result, the present study is one of the few that was able to demonstrate this relationship when focussing on prey capture mechanics. Possibly, this relationship is less frequently observed for prey capture compared to prey processing because, regardless of prey type, the initial capture of prey requires a higher amount of variability.     

Low-temperature tolerance of juvenile tarpon <Emphasis Type="Italic">Megalops atlanticus</Emphasis>

The tarpon Megalops atlanticus is a tropical to subtropical species whose pole-ward distribution is thought to be limited by low water temperatures. In the western north Atlantic Ocean juvenile tarpon occur in estuaries of the South Atlantic Bight (SAB) north of Florida near the northern limit of its distribution, but it is currently unknown whether these individuals can survive winter, grow to maturity, and contribute to the adult population. As a first step to determine whether juvenile tarpon can survive winter conditions in the SAB, we conducted laboratory experiments to estimate minimum lethal temperatures of tarpon exposed to 1) ambient fluctuating winter water conditions and 2) a constant rate of temperature decline. Juvenile tarpon exposed to ambient winter water conditions had a mean ± standard deviation (SD) minimum lethal temperature of 13.7 ± 3.4 °C. When exposed to a constant rate of temperature decline (2 °C day^?1), mean ± SD minimum lethal temperature (9.2 ± 0.8 °C) was lower than when tarpon were exposed to ambient fluctuating conditions. A combination of our results with all published data on the cold tolerance of juvenile tarpon resulted in an overall mean ± SD minimum lethal temperature of 12.0 ± 2.8 °C. Based on available long-term temperature records from SAB estuaries, overwinter survival of juvenile tarpon is unlikely in most aquatic habitats (e.g., tidal creeks, flats, open water). Similar to other estuarine transient fishes, juvenile tarpon likely exploit seasonably favorable nursery habitats and then migrate to other locations to overwinter.     

The effects of intraspecific competition on the prey capture behavior and kinematics of the bluegill sunfish, Lepomis macrochirus

Competition has broad effects on fish and specifically the effects of competition on the prey capture kinematics and behavior are important for the assessment of future prey capture studies in bony fishes. Prey capture kinematics and behavior in bony fishes have been shown to be affected by temperature and satiation. The densities at which bony fish are kept have also been shown to affect their growth, behavior, prey selection, feeding and physiology. We investigated how density induced intraspecific competition for food affects the prey capture kinematics of juvenile bluegill sunfish, Lepomis macrochirus. High speed video was utilized to film five bold individuals feeding at three different densities representing different levels of intraspecific competition. We hypothesized that: (1) the feeding kinematics will be faster at higher levels of competition compared to lower levels of competition, and (2) bluegill should shift from more suction-based feeding towards more ram-based feeding with increasing levels of competition in order to outcompete conspecifics for a prey item. We found that, with increased intraspecific competition, prey capture became faster, involving more rapid jaw opening and therefore greater inertial suction, shorter mouth closing times, and shorter gape cycles. Furthermore, the attack velocity of the fish increased with increasing competition, however a shift towards primarily ram based feeding was not confirmed. Our study demonstrates that prey capture kinematics are affected by the presence of conspecifics and future studies need to consider the effects of competition on prey capture kinematics.     

Effects of capture and transmitter attachments on the swimming speed of large juvenile lemon sharks in the wild

The swimming speed of seven large juvenile lemon sharks Negaprion brevirostris following attachment of an external speed-sensing ultrasonic transmitter was significantly higher during the first 18 h after release compared to the average swimming speed obtained >48 h after release. The external speed-sensing transmitter can be used to monitor the voluntary swimming speed of large fishes in the field, but data during the first 24 h period should be excluded from analysis of natural speeds, at least from species similar in behaviour to N. brevirostris .     

Effects of water movement on prey capture and distribution of reef corals

Coral reefs comprise a variety of microhabitats, each with a characteristic pattern of water movement. Variation in flow microhabitat is likely to influence the distribution and abundance of suspension feeders, including the corals. Water flow was measured concurrently with wave heights at 8 depths along the forereef slope in Salt River Canyon, St Croix, U.S.V.I. The greatest flow speeds occurred on the shallow forereef at 7 m depth, where oscillatory wave-induced flow reached speeds over 50 cm s^–1. From 7 m to at least 15 m depth, flow decreased and was primarily bidirectional. Below 15 m depth, flow decreased even further, to less than one fifth of that experienced by shallow corals, and was unidirectional. The relationship between particle capture by the corals Meandrina meandrites and Madracis decactis and water flow was studied in the field. Colony morphology and the resulting modification of flow influenced the relationship of flow to feeding success; prey capture by the branching Madracis colonies increased with flow, while that of the flat Meandrina colonies did not. Such relationships may contribute to differences in distribution of corals of divergent morphologies. In transect surveys from 7 to 45 m depth,; branching and mounding corals with tentacular feeding modes were most common in the shallow forereef habitats, and plating corals with small polyps (ciliary mucus feeders) were ubiquitous in the deeper zones.This paper was presented at the Fifth International Conference on Coelenterate Biology at Southampton, UK in July 1989. A synopsis appears in the Proceedings (Hydrobiologia 216/217: 247–248, 1991).This paper was presented at the Fifth International Conference on Coelenterate Biology at Southampton, UK in July 1989. A synopsis appears in the Proceedings (Hydrobiologia 216/217: 247–248, 1991).     

Modulation of prey capture kinematics in the cheeklined wrasse Oxycheilinus digrammus (Teleostei: Labridae)

The ability to modulate prey capture behaviors is of interest to organismal biologists as it suggests that predators can perceive features of the prey and select suitable behaviors from an available repertoire to successfully capture the item. Thus, behavior may be as important a trait as morphology in determining an organism's diet. Using high-speed video, we measured prey capture kinematics in three cheeklined wrasse, Oxycheilinus digrammus. We studied the effects of three experimental prey treatments: live fish, dead prawn suspended in the water column, and dead prawn pieces anchored to the substrate in a clip. Live prey elicited significantly more rapid strikes than dead prey suspended in the water column, and the head of the predator was expanded to significantly larger maxima. These changes in prey capture kinematics suggest the generation of more inertial suction. With greater expansion of the head, more water can be accelerated into the buccal cavity. The attached prey treatment elicited strikes as rapid as those on live prey. We suggest that the kinematics of rapid strikes on attached prey are indicative of attempts to use suction to detach the prey item. More rapid expansion of the buccal or mouth cavity should lead to higher velocities of water entering the mouth and therefore to enhanced suction. Further modulation in response to the attached prey item, such as clipping or wrenching behaviors, was not observed. J. Exp. Zool. 290:88-100, 2001.     

Age and growth of tarpon,Megalops atlanticus,larvae in the eastern Gulf of Mexico,with notes on relative abundance and probable spawning areas

Synopsis Leptocephali were collected in June 1981 and July 1989 over the continental shelf and slope of the Florida west coast. Tarpon larvae ranged 5.5–24.4 mm standard length (SL) and were the second most abundant leptocephalus species. Sagittae examined with compound microscopes and scanning electron microscopy had increments that were presumed to be formed daily. Increment counts made using the two microscopic techniques were not significantly different. Estimated ages ranged 2–25 days with a growth rate (± standard error) of 0.92 ± 0.04 mm d^–1 The least squares linear regression equation SL = 2.78 + 0.92 (age in days) best described the relationship between estimated age and length. Adult tarpon appear to undergo a substantial spawning migration from inshore areas frequented during spring and summer to offshore spawning grounds. Spawning occurs during May, June, and July, although the spawning season may be of greater duration.     

Modulation of prey capture kinematics and the role of lingual sensory feedback in the lizard Pogona vitticeps

Most organisms feed on a variety of prey that may differ dramatically in their physical and behavioural characteristics (e.g. mobility, mass, texture, etc.). Thus the ability to modulate prey capture behaviour in accordance with the characteristics of the food appears crucial. In animals that use rapid tongue movements to capture prey (frogs and chameleons), the coordination of jaws and tongue is based on visual cues gathered prior to the prey capture event. However, most iguanian lizards have much slower tongue-based prey capture systems suggesting that sensory feedback from the tongue may play an important role in coordinating jaw and tongue movements. We investigated the modulation of prey capture kinematics in the agamid lizard Pogona vitticeps when feeding on a range of food items differing in their physical characteristics. As the lizard is a dietary generalist, we expected it to be able to modulate its prey capture kinematics as a function of the (mechanical) demands imposed by the prey. Additionally, we investigated the role of lingual sensory feedback by transecting the trigeminal sensory afferents. Our findings demonstrated that P. vitticeps modulates its prey capture kinematics according to specific prey properties (e.g. size). In addition, transection of the trigeminal sensory nerves had a strong effect on prey capture kinematics. However, significant prey type effects and prey type by transection effects suggest that other sources of sensory information are also used to modulate the prey capture kinematics in P. vitticeps.     

Linking cranial morphology to prey capture kinematics in three cleaner wrasses: Labroides dimidiatus,Larabicus quadrilineatus,and Thalassoma lutescens

Cleaner fishes are well known for removing and consuming ectoparasites off other taxa. Observers have noted that cleaners continuously “pick” ectoparasites from the bodies of their respective client organisms, but little is known about the kinematics of cleaning. While a recent study described the jaw morphology of cleaners as having small jaw‐closing muscles and weak bite forces, it is unknown how these traits translate into jaw movements during feeding to capture and remove ectoparasites embedded in their clients. Here, we describe cranial morphology and kinematic patterns of feeding for three species of cleaner wrasses. Through high‐speed videography of cleaner fishes feeding in two experimental treatments, we document prey capture kinematic profiles for Labroides dimidiatus, Larabicus quadrilineatus, and Thalassoma lutescens. Our results indicate that cleaning in labrids may be associated with the ability to perform low‐displacement, fast jaw movements that allow for rapid and multiple gape cycles on individually targeted items. Finally, while the feeding kinematics of cleaners show notable similarities to those of “picker” cyprinodontiforms, we find key differences in the timing of events. In fact, cleaners generally seem to be able to capture prey twice as fast as cyprinodontiforms. We thus suggest that the kinematic patterns exhibited by cleaners are indicative of picking behavior, but that “pickers” may be more kinematically diverse than previously thought. J. Morphol. 276:1377–1391, 2015. © 2015 Wiley Periodicals, Inc.     

A comparison of prey capture kinematics in hatchery and wild Micropterus salmoides floridanus: effects of ontogeny and experience

Analysis of high‐speed videography demonstrated that juvenile wild Florida largemouth bass Micropterus salmoides floridanus captured live prey with very rapid movements and large excursions. Hatchery fish of the same age, raised on pelleted feed, however, used slower kinematics with smaller excursions, yielding strikes with a higher degree of 'suction'. Capture events of hatchery Florida largemouth bass fed live prey for the first time were characterized by movements that had smaller excursion measurements than wild fish and resulted in a decreased level of capture success. After five exposures to elusive mosquitofish Gambusia holbrooki , hatchery Florida largemouth bass adapted their behaviour to capture prey at the kinematic level of wild fish.     

Functional morphology of prey capture in the sturgeon,Scaphirhynchus albus

Acipenseriformes (sturgeon and paddlefish) are basal actinopterygians with a highly derived cranial morphology that is characterized by an anatomical independence of the jaws from the neurocranium. We examined the morphological and kinematic basis of prey capture in the Acipenseriform fish Scaphirhynchus albus, the pallid sturgeon. Feeding pallid sturgeon were filmed in lateral and ventral views and movement of cranial elements was measured from video sequences. Sturgeon feed by creating an anterior to posterior wave of cranial expansion resulting in prey movement through the mouth. The kinematics of S. albus resemble those of other aquatic vertebrates: maximum hyoid depression follows maximum gape by an average of 15 ms and maximum opercular abduction follows maximum hyoid depression by an average of 57 ms. Neurocranial rotation was not a part of prey capture kinematics in S. albus, but was observed in another sturgeon species, Acipenser medirostris. Acipenseriformes have a novel jaw protrusion mechanism, which converts rostral rotation of the hyomandibula into ventral protrusion of the jaw joint. The relationship between jaw protrusion and jaw opening in sturgeon typically resembles that of elasmobranchs, with peak upper jaw protrusion occurring after peak gape.     

Effects of reduced glutathione and catalase on the kinematics and membrane functionality of sperm during liquid storage of ram semen

The objective of this study was to evaluate the effects of reduced glutathione (GSH) and catalase (CAT) supplementation on the kinematics and membrane functionality of sperm during the liquid storage of ram semen, cooled at 5 °C, for up to 24 h. Semen samples from four rams were pooled, diluted with Tris-egg yolk extender without antioxidants (control) or supplemented with either CAT (100, 200, and 400 U/mL) or GSH (100, 200, and 400 mM) at a final concentration of 50 × 10⁶ sperm/mL. Sperm kinematics, which was analyzed by computer-assisted sperm analysis (CASA), and membrane functionality, which was analyzed using the hypo-osmotic swelling test (HOST), were determined after the addition of the semen samples at different processing times (fresh/diluted, 1.5, 6, 12, and 24 h, at 5 °C). No significant differences were recorded in the kinematics or membrane functionality between treatments at different times. The supplementation of diluents with 100 and 200 U/mL of CAT prevented the harmful effects of cooling on total sperm motility. No significant differences were observed in progressive sperm motility throughout processing, regardless of the treatment and time of evaluation. Supplementation with 400 mM GSH resulted in an earlier reduction (P < 0.05) of total sperm motility, a decrease in rapid sperm rate and a reduction in curvilinear velocity during incubation, at 5 °C. The cooling induced a reduction (P < 0.05) in the percentage of sperm with a functional plasma membrane (HOST), especially after 1.5 h of incubation. Based on the results of the present study, the addition of CAT (100 and 200 U/mL) reduced the deleterious effects of cooling on total motility in ram sperm maintained at 5 °C for 24 h, although it did not affect the functionality of the sperm membranes. However, the addition of 400 mM GSH caused negative effects on the velocity parameters of the sperm.     

Food capture kinematics of the suction feeding horn shark, Heterodontus francisci

The goal of this study was to examine the feeding kinematics of the horn shark, Heterodontus francisci, a member of the most basal clade of galeomorph sharks, the Heterodontiformes. The accessibility of the food was manipulated to determine if the horn shark modulated capture. Three different methods of presenting food were used to mimic the different positions of prey items found in the natural diet of the horn shark. Food was presented unattached to the substrate, securely attached, or fitted snugly in a tube. Using high-speed video kinematic analysis, capture events were examined. Heterodontus francisci uses inertial suction facilitated by rapid mandible depression and labial cartilage protrusion to capture food. The horn shark conforms to a capture kinematic profile characteristic of both basal and derived inertial suction feeding sharks. Unusual post-capture behaviors include body leveraging, use of the mouth to form a seal over food, and chisel-like palatoquadrate protrusion. When presented with food of different accessibility, Heterodontus francisci used one consistent kinematic pattern for capture that was not modulated. Only post-capture behaviors varied according to food accessibility.