Lee A. Fuiman

Early life history of fish : an energetics approach

1 Introduction.- 2 Gonad formation.- 2.1 Seasonal changes of main constituents.- 2.2 Reproductive effort.- 3 Characteristics of fish reproductive products.- Energy content and composition of mature eggs.- 3.1 Egg size.- 3.2 Caloric value of egg dry matter.- 3.3 Egg composition.- 3.4 Methodological remarks.- 3.5 Concluding remarks.- Factors affecting fish offspring.- 3.6 Genetic factors.- 3.7 Nongenetic internal factors.- 3.8 Biotic external factors.- 3.9 Abiotic external factors.- 3.10 Effect of egg quality on fish offspring.- 4 Endogenous feeding period.- 4.1 Development.- 4.2 Yolk absorption.- 4.3 Body growth.- 4.4 Metabolism.- 4.5 Budgets of energy or matter.- 5 Mixed feeding period.- 5.1 General remarks.- 5.2 Critical periods in fish early life.- 6 Early exogenous feeding period.- 6.1 Development.- 6.2 Feeding.- 6.3 Body growth.- 6.4 Metabolism.- 6.5 Budgets of energy or matter.- 7 Feeding of fish larvae in aquaculture.- 7.1 Evaluation of effects.- 7.2 Live foods v. formulated diets.- References.- Species index.

Development of predator defences in fishes

SummaryA variety of development characteristics, morphological, behavioural, and experiential, contribute to the extreme vulnerability of young fishes to predation. The influence of these characteristics is complicated by the fact that the larval period is one of substantial and rapid change. Yet survival is the ultimate goal;-it is only by reaching maturity that individual fish have the opportunity to reproduce. With such high stakes it is not surprising that predator defences are of major importance during all phases of life. Developmental constraints may limit the defensive options for young fishes. Avoidance behaviours, which reduce the likelihood of encountering a predator or of being attacked by it, are particulaly evident in the youngest stages. Here size, coloration and dispersal are used to help elude the predators attention. As fishes grow and acquire greater morphological and behavioural sophistication, there is more scope for predator evasion when avoidance fails. Older fishes are increasingly able to respond to external stimuli and can detect and react to predators or join conspecifics in common defence (schooling). Behavioural development is not simply a consequence of growth and the concomitant physical alterations of the body; it is also mediated by experience that comes through interaction with the physical and biotic environment. Predispositions to respond to experience may be a product of evolutionary history. Although mortality rates decline markedly with development and maturity, changes in size or behaviour can render fishes vulnerable to new suites of predators. Effective predator avoidance can compromise other activities, such as foraging, and individuals may be forced to reconcile conflicting demands. Developmental niche shifts that occur, for example, when certain size classes take refuge in less profitable feeding habitats, represent one such trade-off. Niche shifts may also be mediated by the influence of the programme for morphological development on sensory or behavioural capabilities. In addition to all of these developmental consderations, natural variations in environmental conditions — such as temperature, photoperiod, predator density and variety, and presence of alternative prey — represent additional challenges to predator defences during the rite of passage from birth to reproduction.

The cost of foraging by a marine predator, the Weddell seal Leptonychotes weddellii: pricing by the stroke.

SUMMARY Foraging by mammals is a complex suite of behaviors that can entail high energetic costs associated with supporting basal metabolism, locomotion and the digestion of prey. To determine the contribution of these various costs in a free-ranging marine mammal, we measured the post-dive oxygen consumption of adult Weddell seals (N=9) performing foraging and non-foraging dives from an isolated ice hole in McMurdo Sound, Antarctica. Dives were classified according to behavior as monitored by an attached video-data logging system (recording activity, time, depth, velocity and stroking). We found that recovery oxygen consumption showed a biphasic relationship with dive duration that corresponded to the onset of plasma lactate accumulation at approximately 23 min. Locomotor costs for diving Weddell seals increased linearly with the number of strokes taken according to the relationship: locomotor cost =– 3.78+0.04 × stroke number (r2=0.74, N=90 dives), where locomotor cost is in ml O2 kg–1. Foraging dives in which seals ingested Pleuragramma antarcticum resulted in a 44.7% increase in recovery oxygen consumption compared to non-foraging dives, which we attributed to the digestion and warming of prey. The results show that the energy expended in digestion for a free-ranging marine mammal are additive to locomotor and basal costs. By accounting for each of these costs and monitoring stroking mechanics, it is possible to estimate the aerobic cost of diving in free-ranging seals where cryptic behavior and remote locations prevent direct energetic measurements.

Ontogeny of routine swimming activity and performance in zebra danios (Teleostei: Cyprinidae)

Zebra danios, Danio rerio, 3–39 mm long, were studied to quantify ontogenetic changes in routine (spontaneous) swimming. Swimming speeds and mean acceleration rate increased during the larval period with the most rapid changes occurring when fish were between 5 and 15 mm long. At larger sizes, the rate of increase in performance was small. This pattern presumably resulted from morphological changes which also proceeded rapidly in larvae and levelled off towards adulthood. Swimming bouts began with either a large (105°) or a small (3°) turn. Turning angle changed with size apparently due to hydrodynamic conditions, as indexed by Reynolds numbers (Re). Larvae spent 98% of the time in the viscous and intermediate hydrodynamic regimes, of which 90% occurred at an Re of less than 110, and 23% was in the viscous regime (Re<30). Larvae made exclusively small turns when the bout was in the viscous regime (Re<23) and exclusively large ones in the intermediate regime (75<Re<270). Other species show similar rates of travel at lengths between 3 and 7 mm. At larger sizes, the zebra danio, Pacific mackerel, Scomber japonicus, and red sea bream, Pagrus major travel much greater distances per unit time. When their different sizes and rates of development were taken into account, the majority of species eamined showed similar performance levels throughout the larval period. Two species that cover small distances per unit time at a given length (northern anchovy, Engraulis mordax, and Atlantic herring, Clupea harengus) showed performance comparable to that of faster species when their prolonged larval period was taken into account. The implications of these ontogenetic changes in swimming performance for the development of foraging and anti-predator behaviour are discussed.

The role of the sensory systems of herring larvae in evading predatory fishes

Herring (Clupea harengus L.) larvae, ranging from 8–35 mm T.L. were subjected to predation by juvenile herring and sprats (Sprattus sprattus L.) ranging from 80–160 mm T.L. Responses to attacks and non-threatening encounters were recorded by a TV system operated with infra-red light, which was invisible to both predator and prey. Records were made in both light and dark with larvae before and after the otic bullae filled with gas, before and after lateral line canal formation, and before and after chemical ablation of the neuromasts with streptomycin. Larvae often responded with a C-start, turning away from the stimulus source, both in dark and light. Attacks on larvae occurred only in the light. Responsiveness to attacks was very low in the smaller larvae but increased as the otic bulla filled with gas and the lateral line canal developed. Larger larvae responded more often to attacks than to non-threatening encounters with predators. Vision seems to inhibit unnecessary responses since responsiveness was lower in the light than the dark for non-threatening encounters. Response distances were generally short, only 2–4 cm, with no substantial differences associated with sensory capability.

BEHAVIOR AND RECRUITMENT SUCCESS IN FISH LARVAE: REPEATABILITY AND COVARIATION OF SURVIVAL SKILLS

Survival of larvae of highly fecund fishes is often considered to be random, although some investigators have hypothesized that survivors are exceptional individuals. If behavior is important to survival, individuals that perform both well and repeatably will be favored. We conducted experiments on red drum larvae (Sciaenops ocellatus, mean length = 7.7 mm) to assess individual variability in skills related to foraging and predator evasion. We measured routine swimming speed and, for responses to two startle stimuli, response score, latency, distance, duration, and speed. We tested 100 larvae five times each. A large proportion of larvae exhibited repeatable performance for 10 of the performance variables. However, repeatability (or performance level) in one skill was not correlated with repeatability (or level) in an independent skill, except for a positive correlation between acoustic and visual response scores. This result suggested that the level of attentiveness to predators varies among individuals....

Function of the Free Neuromasts of Marine Teleost Larvae

Most species of marine teleosts have very small transparent larvae at hatching, with total lengths from about 1.5 to 8 mm. The eyes may or may not be pigmented at this time, but they always become functional when the larvae commence feeding a few hours to a few days after hatching.Feeding seems to be mainly a visual process, and the larvae of only a few species, such as Dover sole, Solea solea, are known to feed in darkness(Blaxter 1969).All species examined have free neuromast organs distributed over the head and body as superficial hillocks. These hillocks, which are very large relative to the body of the larva, have gelatinous cupulae projecting into the surrounding water.Larval neuromasts are well described by Iwai (1980) in several species including the goldfish(Carassius auratus), sea bass (Lateolabrar japonicus), black porgy (Acanthopagrus schlegeli), and right-eye flounder (Kareius bicoloratus).Disler(1971) followed the changes in number and distribution of the free neuromasts during the development of the sturgeon (Acipenser stellatus), chum salmon(Oncorhynchus keta), and several freshwater percids and cyprinids.Later work on gadoids (Fridgeirsson 1978), northern anchovy (Engraulis mordar)(O’Connell 1981), Atlantic herring (Clupea harengus)(Blaxter et al.1983a), Atlantic halibut(Hip-poglossus hippoglossus) (Blaxter et al.1983b), and plaice(Pleuronectesplatessa) and turbot (Scophthalmus marimus)(Neave 1986)confirmed the earlier findings, showing the increase in numbers with age and also the modifications that occur during the metamorphosis of flatfish.

A killer appetite: metabolic consequences of carnivory in marine mammals ☆

Among terrestrial mammals, the morphology of the gastrointestinal tract reflects the metabolic demands of the animal and individual requirements for processing, distributing, and absorbing nutrients. To determine if gastrointestinal tract morphology is similarly correlated with metabolic requirements in marine mammals, we examined the relationship between basal metabolic rate (BMR) and small intestinal length in pinnipeds and cetaceans. Oxygen consumption was measured for resting bottlenose dolphins and Weddell seals, and the results combined with data for four additional species of carnivorous marine mammal. Data for small intestinal length were obtained from previously published reports. Similar analyses were conducted for five species of carnivorous terrestrial mammal, for which BMR and intestinal length were known. The results indicate that the BMRs of Weddell seals and dolphins resting on the water surface are 1.6 and 2.3 times the predicted levels for similarly sized domestic terrestrial mammals, respectively. Small intestinal lengths for carnivorous marine mammals depend on body size and are comparatively longer than those of terrestrial carnivores. The relationship between basal metabolic rate (kcal day(-1)) and small intestinal length (m) for both marine and terrestrial carnivores was, BMR=142.5 intestinal length(1.20) (r(2)=0.83). We suggest that elevated metabolic rates among marine mammal carnivores are associated with comparatively large alimentary tracts that are presumably required for supporting the energetic demands of an aquatic lifestyle and for feeding on vertebrate and invertebrate prey.

Ontogeny, growth, and the recruitment process

Every individual of a population is challenged daily by circumstances that demand certain levels of performance if the organism is to survive long enough to contribute to recruitment, no matter how recruitment is defined. The challenges faced by fish larvae are especially arduous and numerous because of their relatively small size, which limits their abilities to thwart predators, starvation, and transport to detrimental environs (Miller et al., 1988; Fuiman and Magurran, 1994). Performance — behavioural, physiological or otherwise — is the key to survival and, hence, recruitment. It can be measured for any of a multitude of processes that operate from the subcellular through whole-organism levels. Natural selection acts on the entire phenotype — morphology, physiology and behaviour — to shape the performance capacities of individuals. Detailed knowledge of these performance capacities and the magnitude of their variation is essential for a full understanding of the mechanisms that ultimately determine recruitment.

Three-dimensional movements and swimming activity of a northern elephant seal ☆

We attached a video system and data recorder to a northern elephant seal to track its three-dimensional movements and observe propulsive strokes of the hind flippers. During 6 h of recording, the seal made 20 dives and spent 90% of the time submerged. Average dive duration, maximum depth and swimming speed were 14.9 min+/-6.1 S.D., 289 m+/-117 S.D. and 1.1 m s(-1)+/-0.12 S.D., respectively. The distance swum during a dive averaged 925 m+/-339 S.D., and the average descent and ascent angles were 41 degrees +/-18 S.D. and 50 degrees +/-21 S.D., respectively. Dive paths were remarkably straight suggesting that the seal was navigating while submerged. We identified three modes of swimming based on the interval between propulsive strokes: continuous stroking; stroke-and-glide swimming; and prolonged gliding. The seal used continuous stroking from the surface to a mean depth of 20 m followed by stroke-and-glide swimming. Prolonged gliding started at a mean depth of 60 m and continued to the bottom of dives. For dives to depths of 300 m or more, 75% of the descent time was spent in prolonged gliding and 10% in stroke-and-glide swimming, amounting to 5.9-9.6 min of passive descent per dive. Average swimming speed varied little with swimming mode and was not a good indicator of propulsive effort. It appears that the seal can use prolonged gliding to reduce the cost of transport and increase dive duration. Energetically efficient locomotion may help explain the long and deep dives that routinely exceed the theoretical aerobic dive limit in this species.