Pelagic Marine Fish Research Articles

Contrasts in the capacity and underlying mechanisms for compensatory growth in two pelagic marine fishes

The widespread capacity for teleost fishes to engage in compensatory growth suggests there are costs or trade-offs that constrain normal growth to sub-maximal rates. Some potential trade- offs include behavioral conflicts between foraging and avoiding predators, and physiological aspects of energy allocation between synthesis of new tissue and functional demands of metabolism and maintenance. We examined the capacity for compensation and some potential underlying mecha- nisms in juveniles of 2 northern Pacific fish species, walleye pollock Theragra chalcogramma and sablefish Anoplopoma fimbria. Fish were deprived of food for 2 to 3 wk, then returned to ad libitum rations. Growth rates were subsequently compared to those for continually fed fish for up to 16 wk, and potential trade-offs in behavior (food consumption, routine swimming speeds, and response to a predator) and physiology (indexed by critical swimming speeds) were examined during 3 time peri- ods: immediately after deprivation, after 4 wk of ad libitum rations, and after 9 wk. We distinguished between routine swimming speeds, which indicate volitional motor activity, and critical swimming speeds, which estimate physiological capacity by forcing fish to swim to exhaustion against an increasing current. Previously deprived walleye pollock exhibited a clear, sustained capacity for accelerated growth, allowing them to quickly catch up in size to continually fed fish. Sablefish, how- ever, exhibited only a minor level of growth compensation. Underlying mechanisms of compensatory growth also differed between the 2 species. Previously deprived walleye pollock increased food con- sumption to levels 3 to 4× greater than those of control fish and reduced energy expenditure by low- ering routine swimming speeds. Compensating sablefish did not differ from control fish in consump- tion rates or routine swimming, but had lower critical swimming speeds than control fish, suggesting a trade-off in energy allocation. Responses to a simulated predator threat did not differ between pre- viously deprived and continually fed fish of either species. The experimental results are suggestive of different mechanisms, behaviorally based for walleye pollock and physiologically based for sablefish, associated with accelerated growth. The differences between the 2 species in integrated processes of growth, behavior, and physiology are likely to be a function of their contrasting life history strategies and different baseline growth rates.

The “school trap”: a mechanism promoting large‐amplitude out‐of‐phase population oscillations of small pelagic fish species

Small coastal pelagic marine fishes often form mixed schools containing two or more species. Individuals of a less abundant species, which are entrained in schools that are dominated numerically by a more abundant species, may be adversely impacted. This may help to account for an observed pattern of strong alternations in dominance between sardines and anchovies in a number of regions of the world’s oceans.

The Effect of Freeze-Thawing on the Magnetic Resonance Imaging Parameters of Cod and Mackerel

Magnetic Resonance Imaging (MRI) was used to measure the MR parameters of water (T1, T2, Tsat1, Msat, M0and the Magnetisation Transfer (MT) rate) in fresh and frozen-thawed cod (Gadus morhua) and mackerel (Scomber scombrus); those species were chosen to be representative of the demersal and pelagic marine fish, respectively. Samples of a cod were obtained ‘fresh’ from a local fish market and as cod fillets in an Individually Quick Frozen (IQF) state. The extent of deterioration during storage was monitored over 2, 4, 8 and 12 wk periods. It was found that T1, Tsat1and MT rate were particularly sensitive to the effects of frozen storage.

Fish larval nutrition: a review of recent advances in the roles of amino acids

Marine pelagic fish eggs from various latitudes contain up to 50% of the total amino acid pool as free amino acids (FAAs). The FAA pool is established during final oocyte maturation and seems to derive from the hydrolysis of a yolk protein. During yolk resorption, the FAA pool is depleted and reaches low levels at first feeding. The FAA are predominantly used as metabolic fuel, but they are also utilized for body protein synthesis. Amino acids are also important catabolic substrates after the onset of first feeding and may account for 60% or higher of the energy dissipation. Since growth is primarily an increase in body muscle mass by protein synthesis and accretion and fish larvae have very high growth rates, they have a high dietary requirement for amino acids. Fish larvae that develop stomachs late in development have a low proteolytic and absorptive capacities of the digestive systems at first feeding. In vivo studies have shown higher absorption of FAA than peptides and protein bound amino acids from the larval gut in the early stages of marine fish larvae. In the ocean, marine fish larvae obtain a large supply of FAA by consuming plankton after first feeding. The FAA composition of live feed used in aquaculture may to some extent be manipulated within rearing conditions and species and strain selection. While microdiets are a promising feed for larval fish, no satisfactory techniques have at present been developed that allows delivery of high contents of FAA. New techniques using liposomes have the potential to alleviate this problem.

Short communication. First record of Torticaecum sp. (Trematoda: Didymozoidae) in the chaetognath Serratosagitta serratodentata (Krohn, 1853) from Caribbean waters

From samples collected in the Caribbean Sea during February, March, May and August 1991, a total of 22 508 holoplanktonic chaetognaths were caught. During the analyses of the samples, one non-cysted specimen of didymozoid metacercaria was found in the coelom of the chaetognath Serratosagitta serratodentata (prevalence 0.004%). Owing to the lack of an authentic stomach and the morphology of the intestine, this trematode seems to belong to the Torticaecum larval type. This is the first report of both the chaetognath species as a host and the geographical locality for this parasite. Trematode larvae from the family Didymozoidae have been previously recorded in animals from the planktonic realm (Dollfus, 1963; Madhavi, 1968; Nagasawa and Marumo, 1979; Theodorides, 1989). Cable and Nahhas (1962), based on the presence of one single larva recorded in adult cirripedians, assumed that these crustaceans were intermediate hosts. Yamaguti (1970) mentioned small fish as possible paratenic hosts, as large marine pelagic fish, and more rarely freshwater fish species, are the final hosts most of the time (Yamaguti, 1971). Reports of these types of trematodes as parasites in zooplankton communities are extremely scarce around the world. Regarding chaetognaths as hosts, Dollfus (1960) registered a larval form (Metacercaria sagittae) in Sagitta enflata in Castiglione (Algeria), Reimer et al. (1971) reported a didymozoid metacercaria in Sagitta elegans in the North Sea and Oresland (1986) found them in Sagitta setosa from samples collected off Plymouth (UK). In all cases, the authors did not specify whether the parasites found belonged to the Monilicaecum or Torticae- cum larval type. On the other hand, Reimer et al. (1975) reported eight chaeto- gnath species from the Atlantic Ocean as being parasitized with metacercaria of the family Didymozoidae, apparently of the Monilicaecum type (Shimazu, 1978). The purpose of this work is to describe the metacercaria of Torticaecum found in the coelom of Serratosagitta serratodentata (Krohn, 1853) and to report the Caribbean Sea as a new geographical area for this parasite.

Design and operation of Atlantic halibut, Hippoglossus hippoglossus L., egg incubators

An egg incubator system specially designed to meet the requirements of Atlantic halibut, Hippoglossus hippoglossus L., eggs is described. Compared to other pelagic marine fish eggs, halibut eggs are frequently found to be heavy and lacking in buoyancy in seawater incubators. The biological features of halibut eggs which explain the choice of system design are discussed. In addition to the biological requirements, the system described is designed to meet the demands of commercial hatcheries where handling of large egg masses with a minimum of labour is needed. The incubation method has proved by experience to give high survival rates throughout egg development.

Utilisation of yolk fuels in developing eggs and larvae of European sea bass ( Dicentrarchus labrax)

Developing eggs and larvae of European sea bass ( Dicentrarchus labrax) maintained in filtered sea water (40 gl −1) at 18°C, were measured for oxygen uptake, contents of free amino acids (FAA), protein, fatty acids (FA), and volumes of yolk-sac and oil globule. Newly spawned eggs had a dry weight of 90 μg egg −1 and an egg diameter of 1.14±0.03 mm. The yolk was quickly absorbed during the embryonic and the early larval stages and was 95% depleted by 100 h post fertilisation. The depletion rates of the FAA were somewhat faster than the rate of absorption of the general yolk matter and were almost complete by 80 h post fertilisation. The oil globule was mainly absorbed after hatching following yolk absorption, and occurred concurrently with catabolism of FA from neutral lipids. Approximately 30% of the oil globule was still present at the presumed onset of exogenous feeding. Overall, FAA appeared to be a significant energy substrate during the egg stage and the early yolk-sac stage while FA from neutral lipids derived from the oil globule seemed to be the main metabolic fuel after hatching. Amino acids from protein seemed to be mobilised for energy in the last part of the yolk-sac stage. This investigation supports accumulating evidence for a common sequence of catabolic substrate oxidation in marine pelagic fish eggs that contain oil globules.

Stress of capture and captivity in kahawai Arripis trutta (Bloch and Schneider) (Perciformes: Arripidae)

Plasma cortisol in wild kahawai ( Arripis trutta), an active pelagic marine fish, immediately after capture by hook and line was 8 ± 5 ng/ml (capture time, 4.9 ± 0.8 min, range 1–11 min). Capture by angling was accompanied by high levels of lactate in the white muscle (46.6 ± 2.8 μmol/g) and moderate plasma lactate levels (8.4 ± 1.0 mmol/l). Peak plasma cortisol concentration in fish after transport to shore in live tanks aboard a boat (1–2 hr post-capture) was 161 ± 31 ng/ml. Cortisol levels in wild-caught kahawai had returned to basal values within 3 days of introduction to a shore-based holding pool. Kahawai reacted violently to confinement in still water in darkened enclosed boxes. This prompted the design and construction of a swim tunnel for holding individual kahawai. Confinement of chronically cannulated kahawai in the swim tunnel resulted in a progressive increase in plasma cortisol; 2 hr after cannulation and confinement in the swim tunnel, plasma cortisol concentration was 112 ± 31 ng/ml. This increased to 233 ± 55 ng/ml after 2 days of confinement. Thus, confinement and cannulation do not appear to be suitable approaches for studying the physiology of this species.

Genetic Divergence in Antitropical Pelagic Marine Fishes (Trachurus, Merluccius, and Scomber) between North and South America

Genetic Divergence in Antitropical Pelagic Marine Fishes (Trachurus, Merluccius, and Scomber) between North and South America

Metabolic aspects of free amino acids in developing marine fish eggs and larvae

Abstract Investigations during the last decade have shown that free amino acids (FAA) abound in marine pelagic fish eggs. The concentration in the egg (about 150 mM) is well above what is typically found in adult teleostean tissues. FAA in fish eggs were initially studied in order to evaluate their role as osmolytes. More recently, however, FAA have been implicated as a fuel in the energy metabolism of developing marine fish eggs and larvae. Further aggregation of data verifies that pelagic eggs of marine teleosts generally have a high content of FAA. The large pool of FAA is almost exclusively contained within the yolk‐sac compartment. The relative composition of the FAA pool shows little interspecific variation. The FAA pool is depleted during development and reaches low levels at first feeding. The observed decline in the FAA content during development is not due to a loss of FAA to the ambient water, but rather results from endogenous metabolic turnover. FAA seem to be utilized to varying extents for ...

Social mechanisms facilitating exploitation of spatially variable ephemeral food patches in a pelagic marine fish

Juvenile walleye pollock, Theragra chalcogramma, are more successful at exploiting spatially variable ephemeral food patches when foraging in groups. This may be attributable to local enhancement and to social facilitation of feeding motivation. Feeding responses of individuals were not independent when fish foraged for spatially variable ephemeral food patches, indicating social cues displayed by successful foragers informed other fish of where food was located (local enhancement). Fish initiated feeding sooner when grouped (social facilitation) than when alone. These results indicate that local enhancement aids individuals in locating food patches, while social facilitation aids in rapid patch exploitation.

Small marine pelagic fish and the threat of fishing; are they endangered?

Evidence of the collapse and recovery of major marine fisheries for pelagic fish species is reviewed, distinguishing the influence of fishing compared with natural (environmental) effects. In one only of the best documented cases (Icelandic spring‐spawning herring) has the stock failed to reappear, after 20 years. Several others, e.g. California sardine, have persisted at 1/000th or possibly less of their peak size for some years before beginning to recover. Fishing has been the main cause of collapse in most but not all cases, due initially to the escalation of catchability as stock size decreases–a phenomenon characteristic of fisheries for pelagic species due to their shoaling habit, ease of detection and vulnerability to modern fishing methods. It is concluded that although the threat of fishing to the continuity of the species is remote, excessive depletion (although avoidable by firm and timely management) is potentially able to cause temporary disappearance of local stock and disruption of the ecosystem.

Alkylmercury species in the equatorial Pacific

HIGH levels of mercury in piscivorous fish constitute a long-standing health hazard1–6. Monomethyl mercury, the main form of mercury in fish, is more toxic than inorganic mercury. But although something is known of the ability of organisms to methylate mercury7,8, the sources, synthesis and fate of methyl mercury in aquatic waters are not well understood. Inorganic and alkylated mercury has been studied in natural waters9–11, precipitation and the atmosphere12,13. We now report evidence of monomethyl and dimethyl mercury in the low-oxygen waters of the equatorial Pacific. The presence of these species has important implications for our understanding of the biogeochemical cycling of mercury in the marine environment. Although the source of monomethyl mercury in open-ocean fish is still unknown, our data show that a pathway exists for the accumulation of methylated mercury in marine pelagic fish.

Rapid shipboard identification and enumeration of pelagic marine fish eggs by a simple photographic technique (note)

Rapid shipboard identification and enumeration of pelagic marine fish eggs by a simple photographic technique (note)

Hatching time in spherical, pelagic, marine fish eggs in response to temperature and egg size

The relationship between egg diameter ((π, mm), temperature (T, °C) and egg development time to hatching (D, in days) was established for approximately spherical, pelagic marine fish eggs as log10D = 7.10 + 0.608 log10 π − 4.09 log10 (T + 26), which explains 82% of the variance of a data set of 140 cases, covering 84 species of teleost fishes, for temperatures from 2.8 to 29.5° C and eggs of 0.6 to 3.4 mm diameter. From this relationship it appears that temperature has 4.7 times as much effect on development time as egg diameter when all variables are expressed in standard deviation units. A discussion of these and related factors is given.

Respiration and growth of larval herring Clupea harengus: relation between specific dynamic action and growth efficiency

Rates of growth and oxygen consumption were measured in larval herring Clupea harengus fed various rations (specific ingestion rate between 0 and 45 % body wt d-l). Initially, growth increased linearily with ingestion. However, it showed a saturating response at highingestion rates, probably caused by a decline in assimilation efficiency. Growth efficiency was expressed as slope of the linear portion of the growth-ingestion (or growth-assimilation) relationship. The efficiency by which ingested (or assimdated) material in excess of maintenance requirements was converted to larval body mass was high, 0.62 (or 0.89), compared to reported estimates in juvenile fish. The oxygen consumption rate (R, ng Oz h-') of anaesthetizedlarvae could beseparated into two components, one proportional to the body mass (W, pg dw) raised to some exponent b and one component proportional to the growth rate (p X W, pg dw d-l): R = 131 WO + 127 p X W. At starvation, the respiration-mass relationship followed the commonly applied allometric equation and had a weight exponent close to the classical Y3. Growing larvae, however, increased their rate of oxygen uptake above the starvation level by ca 127 ng O2 per pg larval dry weight increment (= apparent metabolic cost of growth = specific dynamic action (SDA) expressed relative to growth). T h s en~pirical estimate was close to a theoretical minimum estimate of the cost of biosynthesis and transport but was in the lower range of the empirical values reported for juvenile fish. The observed SDA predicted a growth efficiency very close to that actually observed. The magnitude and composition of SDA in larval and juvenile fish is discussed and it is concluded that the cost of growth is minimum and the efficiency of growth maximum in larval compared to juvenile fish. In an ecological context, this difference may be related to the very steep decline in natural mortality with increasing fish body mass and to the extraordinarily high mortality rates experienced by marine pelagic fish larvae in nature.

Natural mortality of marine pelagic fish eggs and larvae: role of spatial patchiness

Daily instantaneous natural mortality rates of marine pelagic fish eggs and larvae are higher than expected from the trend of mortality rate with dry weight in the sea. The difference between observed mortality rates and those predicted from the trend of mortality with dry weight is directly and positively correlated with the patchiness of their spatial distribution, which suggests that it is caused by the feeding of predators on patches of eggs and larvae. The product of weight-dependent mortality, 5.26 X 10-3 , and 1 + Lloyd's patchiness index predicts mortality rates close to those that have been measured from the field by other workers. Mechanisms that control the spatial patchiness of eggs and larvae may control early life history survival and thereby influence relative year-class strength of adult fish stocks.

The Buoyancy and Vertical Distribution of Eggs of Sprat (Sprattus Sprattus) and Pilchard (Sardina Pilchardus)

Observations on the density of pelagic marine fish eggs have indicated that they are near neutral buoyancy for most of development and have a tendency to become denser towards hatching (see Russell, 1976). However, most of this information has been based on limited laboratory observations on the relative buoyancy of eggs; only a few experiments have given more precise estimates of the absolute density of eggs based on the salinity of water in which they are neutrally buoyant (e.g. Franz, 1910; Sundnes, Leivestad & Iversen, 1965). Recently, a new technique (Coombs, 1981), based on the use of a stable column of continuously graded sea-water concentration has allowed more precise and routine measurements of the density of fish eggs throughout development.

Effects of delayed feeding and temperature on the age of irreversible starvation and on the rates of growth and mortality of Pacific herring larvae

The time periods from exhausion of the yolk to the age of irreversible starvation for Pacific herring Clupea harengus pallasi larvae were 8.5, 7.0 and 6.0 d at 6°, 8° and 10°C, respectively. These periods are within the range perviously measured for Atlantic herring larvae and other temperature zone fish species; they are long compared to the periods for tropical species. The variation in the length of this period is due almost entirely to temperature; the natural logarithm of the time period from fertilization to irreversible starvation is highly correlated (r=0.91) with the mean rearing temperature for 25 species of pelagic marine fish larvae. The rates of growth and mortality, measured for 26 experimental populations of Pacific herring larvae reared at 6°, 8° and 10°C and ten ages of delayed first feeding, decreased and increased, respectively with increasing age of first feeding and increasing temperature. These rates, adjusted for the effects of rearing conditions, were compared with the rates for natural populations of herring larvae. Growth is generally faster in the sea than in experimental enclosures. Two of the eleven estimates of natural mortality rate were high enough to indicate possible catastrophic mass starvation. This is consistent with Hjort's critical period concept of year class formation and it suggests that mass starvation occurs in 18 to 36% of the natural populations of first feeding herring larvae.

Natural environment of the Inner Hebrides—an introduction

SynopsisThe Inner Hebrides have a natural history which, in geological time, dates from the Archaean and, in human history, from the Mesolithic 7000–6500 BC. The archipelago was a great attraction to scientists and historians in the 19th and 20th centuries which has resulted in an extensive literature. It started with Martin in 1703 and following a steady interest for about two centuries has blossomed in many spheres of scientific and other interests over the past 50 years. The islands are geologically outstanding and much pioneering work has been done on their Lewisian and Torridonian basement, Mesozoic fossiliferous sediments and Tertiary ring structures which has been of value in the understanding of the geology of the European and the North Atlantic provinces. The geomorphological features include glaciated landscapes, raised beaches and those caused by marine erosion and accretion.The character of the islands is in great part determined by a mild, wet and windy climate. The soils are mainly ‘mor’ in character with localities of ‘mull’ soils overlying limestone or calcareous sand. Similarly, the vegetation and freshwaters are mainly oligotrophic except when overlying limestone or shell-sand which support meso- and eutrophic communities of plants and animals. There are important assemblies of breeding seabirds in Rhum and Treshnish Isles and wintering flocks of geese and other wildfowl in Islay. The large islands have populations of red deer, grey seals, common seals and otters breed throughout the islands. The Inner Hebrides hold stocks of plants and animals which are genetically distinct from those of the mainland and some have Lusitanian and American affinities.The islands are mainly used for the grazing of sheep and cattle with local small-scale arable cropping in crofting and farming. Forestry is possible only in the sheltered parts of the larger islands or in small sheltered islands; the main crops are sitka spruce and lodgepole pine but there are broadleafed woodlands around large houses in many islands and gardens with exotic, sub-tropical plants, shrubs and trees. There are pelagic and demersal marine fisheries, shell fisheries and fish farms mainly growing salmon, rainbow trout and mussels. The mineral resources on a commercial scale, are minor. The nature conservation interest is high with two National Nature Reserves (including Rhum) and 62 Sites of Special Scientific Interest.