Showing papers in "Fish Physiology in 1997"

4 Feeding At Depth

Abstract: Publisher Summary This chapter discusses the feeding habits and deep-sea energetics of deep-sea fishes. Direct evidence concerning the feeding habits of deep-sea fishes comes principally from the analysis of gut contents. Deep-sea fishes feed extensively on demersal prey whose distributions are closely associated with the bottom of the sea; however, many demersal fishes feed principally on vertically migrating mesopelagic organisms, such as myctophids and cephalopods. The presence of pelagic prey in the diets of demersal fishes has been interpreted both as an evidence of the occurrence of mesopelagic prey near the bottom and of off-bottom migrations by some demersal species into the mesopelagic realm to feed. Most demersal deep-sea fish species are microphagous, preying on small benthopelagic and epibenthic invertebrates, especially crustaceans. A special subguild of benthivores is adapted as durophages, capable of crushing thick-shelled mollusks and other armored invertebrates. The chemical composition of demersal fishes is also correlated with buoyancy mechanisms. Benthic and benthopelagic species with swim bladders have lower water contents and higher skeletal ash, nitrogen, carbon, and energy contents than do benthopelagic species without swim bladders.

8 Sensory Physiolog

Abstract: Publisher Summary This chapter discusses the sensory physiology of deep sea fishes. The olfactory receptor cells are located in an epithelium lining the floor of the nasal capsule and this epithelium is typically folded into olfactory lamellae. The geometry and number of olfactory lamellae within the nasal capsule and the organization of the sensory and nonsensory epithelia vary widely among different fish species. It is predicted that a horizontal patch of detectable pheromone will expand to a maximum range of almost 100 m in about 9 h and then fully dissipate in about 1 day. The pattern of bioluminescent flashing has been observed in two Lampanyctus species, which suggest that the distinct flash patterns may permit species recognition among species that otherwise have similar photophore arrays and also have overlapping habitats. A visual system geared to the interception of bioluminescent signals is found in Bujuculifimzia drukei . The potential for tactile stimuli to play a role in prey detection is shown in antarctic fishes. Antarctic benthic feeders show stereotypical responses to prey touching their pelvic or anal fins.

5 Buoyancy At Depth

Abstract: Publisher Summary This chapter describes the problem of buoyancy faced at deep-sea levels and discusses the swim bladder function of fishes. Fish produce hydrodynamic lift mainly by using their pectoral fins as hydrofoils. The metabolic power needed to propel the hydrofoils through the water can be calculated from drag on the hydrofoils and speed. Another strategy to achieve neutral buoyancy is to build up and maintain a buoyancy device—that is, compensate for the high density of most tissues by including special structures or organs characterized by a very low density. In many species, the swim bladder consists of two chambers, including a thick-walled section in which gas can be deposited and a thin-walled chamber in which gas can be resorbed. In other fishes, the resorbing part of the swim bladder is reduced to a special section of the secretory bladder, called “oval,” which can be closed off by muscular activity. The reduction of the effective gas-carrying capacity of swim bladder blood is brought about by the metabolic and secretory activity of epithelial gas gland cells. The specific gravity of gas increases with gas pressure; hence, the difference between swim bladder gas density and water density decreases with increasing water depth.

3 Distribution and Population Ecology

Abstract: Publisher Summary This chapter elaborates the distribution and population ecology of deep-sea fishes There are two main deep-sea habitats—the pelagic and benthic realms—and the deep-sea fish faunas that live in these two habitats are quite different Many fishes of the epipelagic regions belong to well-known and familiar groups, such as the tunas, swordfish and marlins, flying fish, and jacks Mesopelagic and bathypelagic fishes are taxonomically quite different from those associated with epipelagic regions The distribution of individual species groups and of community assemblages, which forms the basis for biogeographic schemes, suggests a few large pelagic faunal regions These regions are characteristic of different parts of the ocean and generally follow the topography and the overall temperature structure and circulation patterns of the ocean It is found that although mesopelagic fish practice some feeding selectivity, there is broad overlap in the diets of many species Midwater fish at times appear to switch to whatever is most available without much regard for remaining at the appropriate level of the classical food chain

2 Systematics of deep-sea fishes

Abstract: Publisher Summary This chapter discusses the systematics of deep-sea fishes. Deep-sea fishes are often considered as those living below 1000 m and the classification also includes many families and genera that have species occurring between 500–1000 m. The chimaeras are characterized by having a gill cover superficial to four gill openings, among many other anatomical details. The chimaeriformes order of mostly benthopelagic slope-dwelling chondrichthians contains three extant families, of which two, Chimaeridae and Rhinochimaeridae, are known to have some species living at depths below 1000 m. It is found that of 43 families of elasmobranchs, 19 have species with a distribution to or below 500–1000 m. In addition to net hauls, actual sightings or accurate records of depths reached by sharks are few. The snipe eels consist of three genera, with a total of about nine species. They are fragile mesopelagic to bathypelagic fishes, with some said to occur at the ocean surface. The argentines fishes have eggs and larvae that are pelagic. The adults are commonly taken at the margins of continental shelves. Blackchin lanternfishes are mesopelagic to benthopelagic. It is found that adults are most frequently taken at approximately 700–2000 m deep and are placed in three genera.

7 Pressure Effects on Shallow-Water Fishes

Abstract: Publisher Summary This chapter discusses the effects of pressure on shallow-water fishes. The measurements of the concentrations of various substances in organs and/ or tissues are generally performed on tissue samples taken from fishes that are first exposed to high pressure and then decompressed. It is observed that when isolated muscle is pressurized, an increase in maximum twitch tension and in the time taken to reach peak tension is noted. It is found that when isolated gill preparations are incubated in artificial seawater and then submitted to hydrostatic pressure, various changes occur in tissue Na + , K + , and Cl - contents, depending on the experimental pressure. Na + content varies much more rapidly than CI - and K + . In shallow-water fishes exposed to the pressures of about 50–100 ATA, changes in ion contents are principally because of changes in permeability and not to changes in active transport. The effects are mainly an increase in Na + content and a decrease in K + content. The information provided in the chapter shows that a shallow-water fish is able to acclimatize to high pressure and that during this acclimatization physiological changes occur that makes the fishes less sensitive to further compression. The acclimatization of trout and goldfish for at least 21 days at 101 ATA has also been successful, provided that care was taken to compress the fish slowly.

1 What is The Deep Sea

Abstract: Publisher Summary This chapter discusses the morphology of ocean basins, the biophysics of oceans, and oceanic food webs. Most of the 92 natural elements have been detected dissolved in seawater, although the majority occurs only in trace concentrations. The density of seawater plays a key role in ecological processes through determining the stability of oceanic water columns and contributing to the patterns of ocean circulation. Seawater density is determined by three factors: hydrostatic pressure, temperature, and salinity. The presence of trenches along the margins of continents has an important effect on sedimentation regimes, and hence on the ecology of abyssal plains. The oceanic margins impinging on the continental land masses may be either active or passive. Around the Pacific, the margins are active. The crust is buckling down (subducting) beneath the continental land masses to form deep trenches. The trenches trap any sediment transport and turbidity flows that result from mass-wasting events and slope failures triggered by the heightened seismic activity along the continental margins. Some of the most striking eddy features are to be seen in remotely sensed images of either sea-surface temperatures or ocean color of eastern boundary current regions. In the open ocean, the annual quantity and seasonal cycling of primary production is determined by vertical stratification, the light cycle, and the persistence of nutrient supplies.

9 Laboratory and in Situ Methods for Studying Deep-Sea Fishes

Abstract: Publisher Summary This chapter discusses the laboratory and in situ methods for studying deep-sea fishes. Laboratory studies of living, deep-sea fishes require their capture, recovery, and maintenance. Two primary factors influencing the physiological condition of deep-sea fishes collected for laboratory studies are increasing temperature and decompression. Thermally insulated cod ends have been successfully developed and used on a variety of opening–closing midwater trawls and epibenthic sleds to collect and recover living bathypelagic animals for metabolic studies in shipboard laboratories. Temperature-insulated traps also have been employed for collecting scavenging deep-sea fishes. Such traps have been either attached to long pull lines extending to depth from the surface or configured as free vehicles. Free-vehicle acoustic monitoring systems have been developed to study the abundance, movements, and behavior of bathypelagic animals using noninvasive active sonar. The prototypes of these vertically profiling acoustic arrays with single transducers have now been successfully used to study nekton over a seamount and under the Antarctic pack ice.

6 Biochemistry At Depth

Abstract: Publisher Summary This chapter examines the maintenance of biochemical function by fishes in the deep sea. Deep-sea fishes generally have much larger ranges in the depth of occurrence than do shallow-living species and they are more likely to experience large changes in pressure over their life-span. A general theme appearing in biochemical studies of deep-sea fishes is that adaptation to high and variable pressures has entailed the evolution of pressure-insensitive forms of enzymes, rather than enzymes adapted for function at a specific range of high pressures. Interactions among the subunits of multimeric proteins provide a relatively straightforward example of the biochemical effects of pressure because they can be studied as simple equilibria between monomers and polymers. The comparison of lactate dehydrogenase kinetic properties in Sebustolohus suggests that environmental pressures as low as 5 MPa have been sufficient to select for homologs for which substrate binding is relatively unaffected by pressure. It has been found that the deep-sea thermophile, Methanococcus jnnntischii, exhibits pressure-dependent changes in the proportions of three isopranoid ether lipids.