Identification of pelagic eggs of marine fishes by rearing method

Pelagic fish eggs are usually fixed by formalin solution just after collection in the field. Most of these eggs are difficult to be identified to species, because only limited characters are available for identification and considerable changes in structures take place with fixation. In this study, species names of formalin fixed eggs were estimated by comparing their egg diameters and the diameter and number of oil globules with those of the fresh ones identified by the rearing method. Materials were collected in Wakasa Bay in May, August, and October, 1979–1982. Fresh eggs were classified into 40 species or types by the rearing method, but fixed eggs were divided into only 24 types. Comparison of fresh and fixed eggs revealed that 7 out of 24 types of fixed eggs were referable to species, and 13 types were composed of species groups. The rearing method is surely a useful step in indentifying species names and/or species types of fixed eggs.     

Energy density of marine pelagic fish eggs

Analysis of the literature on pelagic fish eggs enabled generalizations to be made of their energy densities, because the property of being buoyant in sea water appears to constrain the proximate composition of the eggs and thus to minimize interspecific variation. An energy density of 1.34 J μl⁻¹ of total egg volume is derived for most species spawning eggs without visible oil globules. The energy density of eggs with oil globules is predicted by     x (J μ1¹) where x is the fractional volume of the oil globule.     

Closure of the micropyle during embryonic development of some pelagic fish eggs

The fine structure of the egg envelope and micropyle was studied in unfertilized and developing eggs of the flounder Paralichthys olivaceus (Temminck & Schlegel), the Alaska pollack Theragra chalcogramma (Pallas), the Japanese tilefish Branchiostegus japonicus (Houttuyn) and the porgy Pagrus major (Temminck & Schlegel). The outer envelope surface of the unfertilized egg was wrinkled, while the inner surface was folded. The micropyle of the unfertilized egg consisted of a shallow vestibule and a distinct canal. The micropylar region of the inner surface of the envelope had a conical- or bowl-shaped protrusion. In developing eggs, the thickness of the envelope decreased and showed smooth outer and inner surfaces which indicated that it had been stretched tangentially at the time of the perivitelline space formation. The lumen of the micropylar canal was invariably occupied with envelope material. We postulate that the blockage of the micropylar canal is a result of the stretching of the envelope. The closure of the micropyle inhibits sperm and external pathogens from penetrating into the perivitelline space and seems to be involved in both the permanent prevention of polyspermy and the protection of the developing embryo from bacterial infection.     

Fine structure of the gills of some Indian air-breathing fishes

A detailed account is given of the structure of the gills of Clarias batrachus, Heteropneustes (= Saccobranchus) fossilis, Channa punctata, Monopterus (= Amphipnous) cuchia and Boleophthalmus boddaerti, based upon light and electron microscopy. In all five species the basic organization into primary and secondary lamellae is apparent but the latter are very much more modified in Monopterus. Three main layers separate the water and blood on the surface of the secondary lamellae. The outer epithelium is usually two layered but may be multilayered close to the origin of the secondary lamellae from the gill filament. The basement membrane is relatively thin and a middle dense layer containing collagen fibrils separates two clear layers. The pillar cells, so characteristic of secondary lamellae, are present in all except Monopterus and flanges from these cells surround the blood channels with the exception of the marginal channels. The latter are lined by endothelial cells which line all the blood channels of Monopterus. The overall thickness of the three layers comprising the water/blood barrier ranges from 1.5 to 13 microns. A number of modifications to this basic organization can be related to the degree of dependence of the different species on air-breathing. Boleophthalmus is the only species commonly found in brackish water and its secondary lamellae have well developed lymphoid spaces between two layers of the epithelium. Special densely-stained regions of the pillar cell flanges were also present in this fish and may have a supporting function.     

Final oocyte maturation in vivo and in vitro in marine fishes with pelagic eggs; yolk protein hydrolysis and free amino acid content

The role of free amino acids (FAA) in oocyte hydration during final maturation has been studied in plaice Pleuronectes platessa and lemon sole Microstomus kitt by in vivo and in vitro measurements. In vitro final maturation was initiated by the administration of human chorionic gonadotropin on large vitellogenic oocytes. The eggs produced in vitro had the same fraction of their total amino acid pool present in the free form as the in vivo hydrated eggs, regardless of whether FAA had been present in the incubation medium or not. The FAA pool in the mature egg was increased 10–15 times that of the oocyte, and the two FAA pool profiles differed strongly. The FAA profiles of the egg groups (intra- as well as interspecific) were almost identical except that the taurine content was lower in eggs in vitro . A major protein band of about 100 kDa was present on SDS electrophoretic gels of oocytes but missing on gels of hydrated eggs. This protein, presumably a lipovitellin, is the most likely origin of the egg FAA pool. We suggest that marine fishes with pelagic eggs share a common mechanism for oocyte hydration whereby partial hydrolysis of specific yolk proteins to FAA creates a major part of the osmotic potential needed for the water influx.     

Comparative structures of the apopolysialoglycoproteins from unfertilized and fertilized eggs of salmonid fishes

The complete amino acid sequence of the major polysialoglycoproteins (PSGPs) from two genera of salmonid fish eggs, Salvelinus and Oncorhynchus, has been determined. The occurrence of tandem repeats of a genus-specific dodeca- and tridecapeptide was found for the apoPSGP of Salvelinus leucomaenis pluvius (Slp) and Oncorhynchus masou ishikawai (Omi), respectively, their amino acid sequences being highly homologous with that of rainbow trout [Salmo gairdneri (Sg)] apoPSGP (*denotes the glycosylation site; mean value of N = approximately 25): H-PSGP(Slp): (Asp-Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-)N H-PSGP(Omi): (Asp-Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-Ser-)N H-PSGP(Sg): (Asp-Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-Gly-)N Within 5-7 min following fertilization H-PSGP is converted to the low-molecular-mass PSGP (L-PSGP) by a specific protease (PSGPase). We have purified L-PSGP from the fertilized eggs of S. leucomaenis pluvius and Oncorhynchus keta (chum salmon) and compared it with rainbow trout egg L-PSGP(Sg) by analysis of their amino acid sequence: L-PSGP(Slp): Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-Asp L-PSGP(Ok): Asp-Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-Ser L-PSGP(Sg): Asp-Asp-Ala-Thr*-Ser*-Glu-Ala-Ala-Thr*-Gly-Pro-Ser-Gly The data support the conclusion that H-PSGP is degraded in vivo 5-7 min after fertilization to L-PSGP by proteolytic cleavage at the position two residues C-terminally to the Pro residue, i.e., -Pro-Ser-Xaa-Asp-(Xaa = either Gly, Ser, or Asp) by the action of PSGPase.     

Patterns of reproductive strategy parameters in some marine teleost fishes

The development of ideas and methods in the quantitative study of the patterns of growth, maturation and longevity in fish is reviewed. Earlier studies on length and age at maturity, von Bertalanffy growth formula parameters, natural mortality and maximum age for clupeiformes, pleuronectiformes, gadiformes and Sebastes spp. are up-dated and extended. The concept of the Growth-Maturity-Longevity (GML) plot is developed and applied. GML plots for the gadiformes and pleuronectiformes occupy the same two-dimensional space, but those for clupeiformes and Sebastes are located differently from them and from each other. The GML parameter suite for long-lived Sebastes spp. is similar to that of certain higher vertebrates of comparable longevity (minke whale and African elephant). It is suggested that the conventional distinction between the growth of fish being indeterminate and that for higher vertebrates determinate is inappropriate; the main difference is whether the approach to the characteristic maximum size is asymptotic , as in fish and some higher vertebrates, or abrupt as in others, including man.     

Distribution of 5'-nucleotidase in muscle of some marine fishes.

A preliminary examination for the purification and characterization of 5'-nucleotidase of fish muscle was carried out and the following results were obtained. 1. The activities of 5'-nucleotidase in the muscles of marine vertebrates and invertebrates (total 11 species) were determined. The highest activity of 5'-nucleotidase was found in Blackrock fish Sebastes inermis, which was then used as a material for estimation of subcellular distribution and solubilization of the enzyme. 2. The 5'-nucleotidase of ordinary muscle of the fish Sebastes inermis was found in nuclear, microsomal and cytosolic fractions. About half of the total activity was found in the nuclear fraction, whereas the highest specific activity was observed in the microsomal fraction. 3. Complete solubilization of the enzyme was attained by using a high concentration of detergent such as Triton X-100, CHAPS, octylglucoside, octylthioglucoside and sodium deoxycholate, suggesting that the enzyme was tightly bound to the membrane. 4. Based on the results of solubility and stability tests, Triton X-100 seemed suitable for solubilizing 5'-nucleotidase from the membrane. 5. Microsomal 5'-nucleotidase was an Mg(2+)-activated enzyme, and no inactivation was observed up to 50 mM of Mg2+.     

Antibacterial activity traceable to the marine blue green alga Trichodesmium erythraeum in the gastro-intestinal contents of two pelagic fishes

Summary The gastro-intestinal contents inHilsa kanagurta (Blkr.) andRastrelliger kanagurta (Cuv). were found to possess antibacterial activity. This could be traced to heavy accumulation ofTrichodesmium erythraeum in the gut. The bloom ofT. erythraeum started this year (1969) about the middle of February and attained a peak during the second week of March. During this period it was found that about 60 to 70 per cent of the fish catches in the inshore waters consistedH. kanagurta andR. kanagurta. Analysis of gut contents of six specimens of each of these two species showed thatT. erythraeum constituted 80 to 90 per cent of the contents. It has been reported previously by the author thatT. erythraeum maintained in cultures in the laboratory and also collected from the sea possesses antibacterial properties. In view of this finding, standard experimental procedures were adopted to determine whether extracts ofT. erythraeum occurring in the gut of the fishes examined also possessed antibacterial activity. It was found thatT. erythraeum collected from the gut ofHilsa andRastrelliger could inhibit both gram-positive and gram-negative bacteria. The gastro-intestinal extract ofHilsa kanagurta andRastrelliger kanagurta collected during nonbloom period ofTrichodesmium showed heavy bacterial and fungal growth. Evidently antibacterial or sterile conditions prevail in the guts of these fishes in a manner similar to what has been observed in polar marine animals by Sieburth (1959 and 1961).     

Sensory nerve endings of highly mobile structures in two marine teleost fishes

Summary With the use of a whole mount silver impregnation technique, sensory nerve endings were located in the connective tissue at the base of the modified pectoral fin ray in the gurnard,Aspitrigla cuculus, and within the perichondrium of the barbel in the goatfish,Mullus surmuletus. The location of these endings and their planar receptory fields in such highly mobile structures, suggests that the sensory endings are proprioceptive in nature and that they are associated in monitoring the positional state of the modified pectoral fin ray and barbel, respectively, during voluntary movement. This investigation addresses itself to the general problem of proprioception in teleost fishes and provides histological evidence for the presence of proprioceptive nerve endings.     

Morphology of unfertilized mature and fertilized developing marine pelagic eggs in four types of multiple spawning flounders

Starry flounder Platichthys stellatus, spotted halibut Verasper variegates, turbot Scophthalmus maximus, and Japanese flounder Paralichthys olivaceus are four commercially cultivated multiple spawning flounders that spawn pelagic eggs. Through appropriate light and scanning electron microscope processing, the shape and surface structures (such as micropyle, pores, pore density, and paten) of unfertilized mature and fertilized developing eggs of the four species were observed and measured. First, individual or intraspecific comparisons of the surface structures of eggs at different developmental stages were made. Second, interspecific differences among the four species at the same developmental stage of unfertilized mature eggs were statistically computed and analyzed through one-way analysis of variance and hierarchical cluster analysis. Eggs of the same species collected at different stages of development tend to be different in morphology. Smoothing of the convoluted egg envelope surface and closure of the micropyle to serve as a final step of the polyspermy-preventing reaction are common after fertilization. Based on detailed morphology of micropyle of just-mature fertilizable eggs, turbot, starry flounder, and Japanese flounder each have a micropyle with a long canal but no distinct micropylar vestibule, type III of Riehl and Götting (Arch Hydrobiol 74:393–402, 1974). In contrast, spotted halibut has a micropyle with a distinct flat micropylar vestibule and a long canal, type II. Envelope surface microstructures, especially those in the micropyle region, are useful characters for egg identification among the four species. Cluster analysis using selected egg characters indicated the highest similarity between turbot and Japanese flounder and that starry flounder is obviously more similar to turbot and Japanese flounder than to spotted halibut.     

Alternative models for species replacement of pelagic fishes

It is well known that the stock abundance of a pelagic fish usually fluctuates and a species of pelagic fish which was dominant in abundance is often taken over by another species. Several alternative models for species replacement among pelagic fishes are presented and analyzed: (A) environmental fluctuation, (B) strong density-dependent reproduction rate, (C) a two-species system with phase variation (density-dependent change of life history traits), (D) a two-species competition system with environmental fluctuation, (E) cyclic advantage relationship among three competitive species, and (F) a two-prey, one-predator system. Different model requires different number of species for the occurrence of species replacement. Three criteria to test each hypothesis from qualitative properties of species replacement are proposed. Possible management policies to decrease the amplitude of stock fluctuations are discussed. As a result, if the catching effort to mackerels which is rare now is large, or if the catching effort to the sardine is still large when it begins to decline in stock abundance, fisheries may be strong destabilizing effect on the stock abundance.     

Aggregations of myctophid fishes with other pelagic fauna

Synopsis Direct underwater observations of myctophid fishes were conducted to 630 m in submarine canyons along the outer margin of the northeast United States continental shelf with the Johnson-Sea-Link II submersible. Data revealed that myctophids occurred in aggregations of other pelagic fauna (e.g., ctenophores, sergestids, amphipods) when densities of the former were low but the latter were high. We suggest that myctophids selectively occur with other pelagic fauna to reduce the probability of direct contact with predators and to take advantage of aggregate search abilities for common prey taxa.     

The evolution of migration and some life history parameters in marine fishes

Synopsis Migration is a common phenomenon in marine fishes but the consequences with respect to life history variation have been little explored. Migration both influences the evolution of other traits and is contigent upon the evolution of other behavioural and demographic characters. The interaction between such factors is illustrated by considering the relationship between the cost of migration in relation to fecundity and the advantages and disadvantages of schooling, a phenomenon hypothesized to favour the evolution of migration. These analyses predict that migratory species will be relatively large, mature late and at a relatively large size and grow relatively fast. Data from north temperate marine fish support these predictions.     

Isotopic evidence of functional overlap amongst the resilient pelagic fishes

The Lake Victoria ecosystem once hosted a diverse fish community dominated by a large species flock of haplochromine cichlids. Today this fish assemblage is highly altered by anthropogenic activities, with at least half of the indigenous species either extinct or very rare. The fauna and flora of the tropic’s largest lake are still in flux, and little is known about even the most basic ecological questions, such as the source of carbon and nitrogen for its spectacular productivity. The actual food-web structure is difficult to determine with results based on traditional gut analysis. At the moment both scientists and conservationists are at odds as to whether there is any evidence of functional replacement or functional overlap amongst the resilient pelagic fishes of Lake Victoria. This study used a static stable isotope model to investigate the source of carbon and the extent of the trophic overlap amongst three pelagic fishes, Rastrineobola argentea, ssichromis laparogramma and Y. fusiformis in the Kenyan waters of Lake Victoria. The δ ¹³C of plants ranged from ?8.8 to ?24.6 $\permil$, while fishes ranged from ?18.6 to ?24.5 $\permil$, suggesting assimilation of mostly C₃ sources for the fish species. On the basis of the isotope model, it is evident that Yssichromis laparogramma, Yssichromis fusiformis , and Rastrineobola argentea obtained from 90 to 97.5$%$, with an average of 94.2$%$, of their food from the same trophic level. The very high degree of overlap in the effective trophic level of these three zooplanktivores has important ecological and conservation implications.     

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

Synopsis The relationship between egg diameter ((, 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 – 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.ICLARM Contribution No. 308.     

DNA identification of gut contents of large pelagic fishes

Partially digested prey items taken from the gut contents of seven species of large pelagic fishes were identified by DNA sequencing of part of the cytochrome b gene. Sequences matched against those of five pelagic prey species held in GenBank® with 99–100% identities. The method is applicable to most gut content identifications, the only limiting factor being the range of control species sequences held in the reference database.     

Trichodinid parasites (Ciliophora: Peritricha) from the gills of some Australian marine fishes

Three species of the genus Trichodina are reported from the gills of marine fishes in south-eastern Tasmania, Australia. Two of these species are new: T. australis n. sp. from five atherinid fish species, Atherinosoma microstoma, Leptatherina presbyteroides, Kestratherina brevirostris, K. esox and K. hepsetoides; and T. nesogobii n. sp. from Nesogobius sp. 1. One previously reported species, T. jadranica Raabe, 1958, was also found on Nesogobius sp. 1.     

Monogamy in marine fishes

The formation of long-term pair bonds in marine fish has elicited much empirical study. However, the evolutionary mechanisms involved remain contested and previous theoretical frameworks developed to explain monogamy in birds and mammals are not applicable to many cases of monogamy in marine fish. In this review, we summarise all reported occurrences of social monogamy in marine fish, which has so far been observed in 18 fish families. We test quantitatively the role of ecological and behavioural traits previously suggested to be important for the evolution of monogamy and show that monogamous species occur primarily in the tropics and are associated with coral reef environments in which territory defence and site attachment is facilitated. However, there is little evidence that obligately monogamous species are smaller in body size than species that can adopt a polygynous mating system. We review the evidence pertaining to six hypotheses suggested for the evolution of monogamous pair bonds: (1) biparental care, (2) habitat limitation, (3) low population density/low mate availability/low mobility, (4) increased reproductive efficiency, (5) territory defence, and (6) net benefit of single mate sequestration. We outline predictions and associated empirical tests that can distinguish between these hypotheses, and assess how generally each hypothesis explains monogamy within and between breeding periods for species with different types of territories (i.e. feeding only or feeding and breeding). Hypotheses (1) and (2) have limited applicability to marine fishes, while hypotheses (3)-(5) have little empirical support beyond the species for which they were designed. However, the role of paternal care in promoting monogamous pair bonds is not explicit in these hypotheses, yet paternal care has been reported in more than 70 monogamous marine fish. We show that paternal care may act to increase the likelihood of monogamy in combination with each of the proposed hypotheses through decreased benefits to males from searching for additional mates or increased advantages to females from sequestering a single high-quality mate. Among species defending breeding and feeding territories, the benefits, both within and between reproductive periods, of sequestering a single high-quality mate (hypothesis 6) appear to be the best explanation for socially monogamous pairs. For species without parental care (i.e. holding only feeding territories), territory defence (hypothesis 5) in combination with the benefits of guarding a large mate (hypothesis 6) could potentially explain most instances of monogamy. Empirical studies of marine fishes over the past two decades are therefore slowly changing the view of monogamy from a mating system imposed upon species by environmental constraints to one with direct benefits to both sexes.