A preliminary study on quantitative relations among growth,reproduction and mortality in fishes

As a quantitative approach to the life histories of fishes, the present paper attempted to predict a relation among reproduction, growth and mortality numerically with a technique of control theory, the discrete maximum principle. A method for predicting the relation was derived on the postulate that natural selection maximized the net reproductive rate subject to a few constraints. The derived method was applied to Atlantic cod and Atlantic herring populations in the Southern Gulf of St. Lawrence as numerical examples. The examples demonstrated that the theoretical reproductive effort and body weight were well consistent with the observed ones every age but the theoretical survival rates were slightly different from the observed ones. For the reasons mentioned below, however, it should be interpreted that the examples rather support the adopted postulate to a certain degree. First, in general, it is very difficult to obtain good estimates of the rates with traditional methods. Second, intense fishing pressure possibly changes the life history parameters to some extent in fish populations. Moreover, the examples also suggested that, to examine the postulate in further detail, similar analyses had to be made with the data of many fish populations on which intense fishing pressure had not been exerted.     

Swimming response of goldfish,Carassius auratus,and the tetra,Hemigrammus caudovittatus,larvae to individual food items and patches

Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (10¹–10³ ind·1^–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches.     

Gene and genome duplications in vertebrates: the one-to-four (-to-eight in fish) rule and the evolution of novel gene functions

One important mechanism for functional innovation during evolution is the duplication of genes and entire genomes. Evidence is accumulating that during the evolution of vertebrates from early deuterostome ancestors entire genomes were duplicated through two rounds of duplications (the 'one-to-two-to-four' rule). The first genome duplication in chordate evolution might predate the Cambrian explosion. The second genome duplication possibly dates back to the early Devonian. Recent data suggest that later in the Devonian, the fish genome was duplicated for a third time to produce up to eight copies of the original deuterostome genome. This last duplication took place after the two major radiations of jawed vertebrate life, the ray-finned fish (Actinopterygia) and the sarcopterygian lineage, diverged. Therefore the sarcopterygian fish, which includes the coelacanth, lungfish and all land vertebrates such as amphibians, reptiles, birds and mammals, tend to have only half the number of genes compared with actinopterygian fish. Although many duplicated genes turned into pseudogenes, or even 'junk' DNA, many others evolved new functions particularly during development. The increased genetic complexity of fish might reflect their evolutionary success and diversity.     

Acidophilic granulocytes of the marine fish gilthead seabream (<Emphasis Type="Italic">Sparus aurata</Emphasis> L.) produce interleukin-1β following infection with<Emphasis Type="Italic"> Vibrio anguillarum</Emphasis>

The fish immune response to Gram-negative bacteria is poorly understood. In this study, we use a monoclonal antibody (mAb) specific to acidophilic granulocytes from the marine fish gilthead seabream (Sparus aurata L.), together with an antiserum specific to interleukin-1 (IL-1) from this species, in order to investigate whether these cells are involved in the immune response against the pathogenic bacterium Vibrio anguillarum and, in particular, in the production of the pro-inflammatory cytokine IL-1. We found that gilthead seabream head-kidney, peritoneal exudate and peripheral blood leukocytes accumulated proIL-1 intracellularly when challenged in vitro with V. anguillarum, whereas only peritoneal exudate and blood leukocytes were able to accumulate proIL-1 following infection. Importantly, the blood leukocytes from infected animals that accumulated proIL-1 were shown to be the acidophilic granulocytes. A rapid mobilization of such cells from the head-kidney to the site of inflammation following infection with V. anguillarum was also observed. This work was supported by the Spanish Ministry of Science and Technology (grants BIO2001-2324-C02-02 and AGL2002-03529, and fellowship to J. García-Castillo), Spanish Ministry of Education, Culture and Sport (fellowship to E. Chaves-Pozo) and Fundación Séneca, Coordination Centre for Research (grant PI-51/00782/FS/01 and fellowship to P. Pelegrín).E. Chaves-Pozo and P. Pelegrín contributed equally to this work.     

Significance of Na+ in the fish pathogen, Vibrio anguillarum, under energy depleted condition

Vibrio anguillarum kills various kinds of fish over salinities ranging from seawater to freshwater. In this study, we investigated the role of Na(+) in V. anguillarum, especially under energy-depleted conditions such as in natural seawater. V. angustum S14, which is a typical marine vibrio, was used for comparison. V. anguillarum only required Na(+) for starvation-survival, but in contrast, V. angustum S14 always required Na(+) for both growth and starvation-survival. In marine vibrios, Na(+) is used in the Na(+)-dependent respiratory chain that produces the sodium motive force (SMF) across the cell membrane. It has been considered that marine vibrios always need a SMF produced by Na(+), however in the case of V. anguillarum, the SMF is not required for growth, but becomes more important for starvation-survival.     

The role of somatostatins in the regulation of metabolism in fish

Somatostatins (SS) are a structurally and functionally diverse family of peptide hormones. Somatostatins possess a wide variety of biological functions, including numerous secretotropic, developmental, and metabolic effects. Studies on fish have revealed considerable insight into the role of SS on the regulation of intermediary metabolism. Somatostatins promote both lipid and carbohydrate breakdown in fish and lamprey. Such actions are mediated by secretotropic effects of SS. For example, SS inhibit insulin (INS); insulin deficiency favors lipolysis and glycogenolysis over lipogenesis and glycogenesis. Somatostatins also directly stimulate the breakdown of stored triacylglycerols (TG) and glycogen in storage tissues. In addition, SS interact with the growth and reproductive axes of fish, findings that suggest SS serve to modulate energy partitioning among various growth, development and reproductive processes.     

The effects of diet composition and ration on biotransformation enzymes and stress parameters in rainbow trout, Oncorhynchus mykiss

Juvenile rainbow trout (Oncorhynchus mykiss) were fed one of three isoenergetic diets varying in protein (35-55%) and lipid content (8-18%), at full satiation levels or half rations for 6 weeks in order to investigate the effects of diet on baseline stress parameters and biotransformation enzyme activity. Growth was greatest in fish fed to satiation on a low protein and high lipid diet. Stress parameters, including plasma lactate, glucose and cortisol concentrations were not significantly affected by dietary treatment or ration. Basal biotransformation enzymes, including glutathione S-transferase (GST) and ethoxyresorufin O-deethylase (EROD) activity, were also unaffected by dietary treatment. Fish exposed to the biotransformation enzyme inducer beta-naphthoflavone did not exhibit an alteration in stress indicators or GST activity; however, EROD activity was increased (87- to 210-fold) in fish receiving all diets and rations. The results of the present study indicate that, unlike mammals, fish may be more recalcitrant to different levels of ingestion of isoenergetic diets varying in protein and lipid concentration with respect to stress responses and the maintenance of basal titers of biotransformation enzymes and their induction.     

The application of image cytometry to viability assessment in dual fluorescence-stained fish spermatozoa

The viability of spermatozoa has been assessed using SYBR 14 staining for DNA of living cells and propidium iodide staining for DNA of degenerate cells. This dual staining was performed on four fish species (Siberian sturgeon, Acipenser baerii; common carp, Cyprinus carpio; tench, Tinca tinca and wels, Silurus glanis) and the proportions of live and dead spermatozoa were assessed by epifluorescence microscopy and image cytometry. Ten phase contrast and epifluorescent images were recorded per sample, corresponding images were overlaid, and the blended images were evaluated for live and dead spermatozoa, represented by green and red fluorescence signals. Live/dead proportions were assessed, after dual thresholding, by imaging software that counted absolute numbers of objects and computed their frequencies. All sperm heads were found to be labelled, emitting either green or red light. Mean numbers of spermatozoa per image were in the ranges 32-113, 61-105, 48-104 and 29-91 for Siberian sturgeon, common carp, tench and wels, respectively. The corresponding proportions of live spermatozoa were in the ranges 83.56-94.59%, 93.92-97.02%, 76.14-97.76% and 79.45-83.76%. Standard deviations did not exceed 5% of the means. The image cytometric system using dual staining with SYBR 14 and propidium iodide was clearly suitable for assessing the viability of freshwater fish spermatozoa.     

Ventilatory frequency indicates visual recognition of an allopatric predator in nai;ve Nile tilapia

Perceiving a possible predator may promote physiological changes to support prey ‘fight or flight’. In this case, an increase in ventilatory frequency (VF) may be expected, because this is a way to improve oxygen uptake for escape tasks. Therefore, changes in VF may be used as a behavioral tool to evaluate visual recognition of a predator threat. Thus, we tested the effects of predator visual exposure on VF in the fish Nile tilapia, Oreochromis niloticus. For this, we measured tilapia VF before and after the presentation of three stimuli: an aquarium with a harmless fish or a predator or water (control). Nile tilapia VF increased significantly in the group visually exposed to a predator compared with the other two, which were similar to each other. Hence, we conclude that Nile tilapia may recognize an allopatric predator; consequently VF is an effective tool to indicate visual recognition of predator threat in fish.     

Effects of chronic hypoxia on inward rectifier K(+) current ( I(K1)) in ventricular myocytes of crucian carp (Carassius carassius) heart

Some ectothermic vertebrates show unusually good tolerance to oxygen shortage and it is therefore assumed that they might, as a defense mechanism, decrease number or activity of ion channels in order to reduce membrane leakage and thereby ATP-dependent ion pumping in hypoxia. Although several studies have provided indirect evidence in favor of this channel arrest hypothesis, only few experiments have examined activity of ion channels directly from animals exposed to chronic hypoxia or anoxia in vivo. Here we compare the inwardly rectifying K⁺ current (I_K1), a major leak and repolarizing K⁺ pathway of the heart, in cardiac myocytes of normoxic and hypoxic crucian carp, using the whole-cell and cell-attached single-channel patch-clamp methods. Whole-cell conductance of I_K1 was 0.5 ± 0.04 nS/pF in normoxic fish and did not change during the 4 weeks hypoxic (O₂ < 0.4 mg/l; 2.68 mmHg) period, meanwhile the activity of Na⁺/K⁺ATPase decreased 33%. Single-channel conductance of the I_K1 was 20.5 ± 0.8 pS in control fish and 21.4 ± 1.1pS in hypoxic fish, and the open probability of the channel was 0.80 ± 0.03 and 0.74 ± 0.04 (P > 0.05) in control and hypoxic fish, respectively. Open and closed times also had identical distributions in normoxic and hypoxic animals. These results suggest that the density and activity of the inward rectifier K⁺ channel is not modified by chronic hypoxia in ventricular myocytes of the crucian carp heart. It is concluded that instead of channel arrest, the hypoxic fish cardiac myocytes obtain energy savings through action potential arrest due to hypoxic bradycardia.