Helpers in fish

Summary Field data show that in the cichlid fish Lamprologus brichardi conspecifics other than the reproducing pair help in brood care and territory maintenance. The expected degree of relatedness between helpers and the eggs or larvae they tend lies between 0.25 and 0.5, decreasing with the helper's age. This decrease might influence the point of time at which helpers depart. Five other endemic Lake Tanganyika cichlids showing rather similar helping behaviour are described.     

Parasite genotypes identify source populations of migratory fish more accurately than fish genotypes

DNA-based assignment of individuals to their population of origin has many applications such as mixed-stock analysis, identifying individuals from protected populations, and elucidating migration patterns. However, low genetic differentiation among populations will cause misassignments. Thus, an alternative means of determining an individual's population of origin is needed in cases where there is little or no neutral differentiation among source populations. Here, we test the hypothesis that parasite genotypes can be used to identify the origins of hosts more accurately than host genotypes. Using microsatellite markers from steelhead trout and their trematode parasites, we show that the odds of correct assignment are four times greater with the parasite's genotypes than with the host's genotypes. Our analyses show that this result is simply explained by the greater genetic structure among populations of the trematode parasite. Recent studies on the comparative genetic structure of other host and parasite species suggest that our results are not unusual or unique to the host-parasite system we studied. Thus, our work indicates that parasites will be useful for a wide range of applied and basic research that requires the assignment of individuals to source populations.     

A model of fish growth

A fish model based upon mass balances is set up. Several of the parameters have been determined by experiments. The remaining parameters are based upon literature values and it was not necessray to find any parameter by calibration. The model was validated with a completely acceptable result.The model includes equations giving the fish growth, the production of ammonia and organic matter, the oxygen consumption, and the influence to the temperature.The model can be used for management of fish farms and as a submodel for a total aquatic system.     

Fatty acids in fish scales

This study represents the first determination of lipids and fatty acids in fish scales. Scales collected from groups of Atlantic salmon reared on fish farms and in experimental tanks were analyzed by chromatography. The complete suite of fatty acids normally found in marine organisms was detected in the scales, with the following fatty acids dominating: 16:0, 18:0, 18:1n9, 20:5n3, 22:6n3 and 24:1n9. Scales contained relatively high levels of furan fatty acids, and the level of cholesterol (2.5–5 mg/g tissue) was much higher than the levels found in the edible parts of marine fishes (0.2–1 mg/g tissue). The fatty acid profile of scales was distinct between groups of salmon originating from different commercial strains reared on the same farm, between salmon groups originating from the same strains but reared at different farms, and between groups of fed and unfed salmon in experimental tanks. Together, these data indicate that the fatty acid composition of fish scales is dependent upon both environmental and genetic factors. The fatty acid composition of fish scales may be used in stock/population identification, for example identification of escaped Atlantic salmon to farm of origin.     

Shadow cinematography of fish larvae

A simple system of shadow cinematography, consisting of a small tungsten halogen lamp, 2 large biconvex lenses and a 16 mm camera, is described for recording the swimming and feeding behaviour of larval fish. The system can be used either with infra-red film to record swimming behaviour independently of ambient light intensity, or with high-resolution film to record food organisms and feeding behaviour. Small plankton organisms of 0.2 mm width can be resolved using high-resolution film. The technique has been used to record the behaviour of plaice larvae (Pleuronectes platessa L.) feeding on the nauplii of Artemia salina L. The perceptive field of the larvae extends to approximately ±60° in azimuth, ±40° in elevation and 1.5 body lengths in range.     

Biomarkers of pyrethroid toxicity in fish

Environmental Chemistry Letters - Pesticides contribute to human welfare by reducing vector-borne diseases and protecting crops against pests. Insecticides are the most widely employed pesticides...     

Microplastic contamination in Great Lakes fish

Freshwater ecosystems, generally adjacent to human population and more contaminated relative to adjacent marine ecosystems, are vulnerable to microplastic contamination. We sampled 7 species of fish from Lake Ontario and Lake Superior and assessed their gastrointestinal (GI) tracts to quantify ingested microplastics and other anthropogenic particles. A subset of the microparticles were chemically analyzed to confirm polymer types and anthropogenic origins. We documented the highest concentration of microplastics and other anthropogenic microparticles ever reported in bony fish. We found 12,442 anthropogenic microparticles across 212 fish (8 species) from nearshore Lake Ontario, 943 across 50 fish (1 species) from Humber River, and 3094 across 119 fish (7 species) from Lake Superior. Fish from Lake Ontario had the greatest mean abundance of anthropogenic microparticles in their GI tracts (59 particles/fish [SD 104]), with up to 915 microparticles in a single fish. Fish from Lake Superior contained a mean [SD] of 26 [74] particles/fish, and fish from Humber River contained 19 [14] particles/fish. Most particles were microfibers. Overall, ≥90% of particles were anthropogenic, of which 35-59% were microplastics. Polyethylene (24%), polyethylene terephthalate (20%), and polypropylene (18%) were the most common microplastics. Ingestion of anthropogenic particles was significantly different among species within Lake Ontario (p < 0.05), and the abundance of anthropogenic particles increased as fish length increased in Lake Ontario (ρ = 0.62). Although we cannot extrapolate the concentration of microplastics in the water and sediments of these fish, the relatively high abundance of microplastics in the GI tracts of fish suggests environmental exposure may be above threshold concentrations for risk.     

Odorous volatile components in Ayus fish

Volatile components in Ayus (fish in Japan) having bad smell were analyzed by freeze‐vacuum distillation and gas chromatography/mass spectrometry to clarify the origin of the smell. Nitrogen heterocyclic compounds might be the origin.     

Economics of harvesting age-structured fish populations

A generic age-structured model is developed to derive analytical results on optimal harvesting. Given two age classes, knife-edge selectivity, and no stock-dependent harvesting cost, the steady state is a unique saddle point. Adding harvesting cost does not alter the uniqueness, given that the utility is linear. Under specific conditions such as nonselective gear, optimal harvesting is proved to be a stationary cycle that represents pulse fishing. Optimal steady states are different if age-structured information is ignored and optimization is based on traditional biomass variables. This implies that the existence of optimal sustainable harvesting depends on age-structured information. Given a specific set of conditions such as low interest rate and knife-edge selectivity, optimal harvesting converges toward a unique saddle point independently of the number of age classes.     

Economics of harvesting age-structured fish populations

A generic age-structured model is developed to derive analytical results on optimal harvesting. Given two age classes, knife-edge selectivity, and no stock-dependent harvesting cost, the steady state is a unique saddle point. Adding harvesting cost does not alter the uniqueness, given that the utility is linear. Under specific conditions such as nonselective gear, optimal harvesting is proved to be a stationary cycle that represents pulse fishing. Optimal steady states are different if age-structured information is ignored and optimization is based on traditional biomass variables. This implies that the existence of optimal sustainable harvesting depends on age-structured information. Given a specific set of conditions such as low interest rate and knife-edge selectivity, optimal harvesting converges toward a unique saddle point independently of the number of age classes.     

Simulating fish production using exponential smoothing

The variation over time of the total annual production of pe and the United Kingdom has been described quantitatively using the exponential smoothing technique. The exercise was repeated on annual mackerel landings for the same two countries. It is suggested that in some cases, the production figure for the current year can be used to simulate the following year's value. The greater variations in South Africa's annual production probably gave rise to the poorer results for these data.     

Optimal harvesting of ecologically interdependent fish species

The optimal exploitation of a two-species predator-prey system is considered, using Lotka-Volterra-type equations. Due to the density-dependence of ecological efficiency, both species should be harvested simultaneously over a range of relative prices. Beyond the limits of this price range, either the prey species should be utilized indirectly by harvesting the predator, or the predator should be eliminated to maximize the prey yield. Neglecting harvesting costs, the simultaneous harvest of prey and predators requires that a unit of prey biomass increase in value by being “processed” by predators. Certain results from single-species fishery models are shown not to apply to multispecies models. These are as follows: (i) Optimal regulation of a free access fishery may call for subsidizing instead of taxing the harvest of predator species. (ii) Increasing the discount rate may, at “moderate” levels, imply that the optimal standing stock of biomass increases instead of decreasing. (iii) A rising price or a falling cost per unit fishing effort of a species may raise and not lower the optimal standing stock of that species.     

Herbivory by the myctophid fish Ceratoscopelus warmingii

During a study of midwater fish feeding in the oligotrophic North Pacific gyre in August 1978, nine specimens of a tropical-subtropical myctophid, Ceratoscopelus warmingii, were found to have been feeding on mats of diatoms, Rhizosolenia spp. Chemical analyses of the intestinal contents of several additional specimens showed significantly elevated levels of diatom degradation products. Therefore, C. warmingii, although known to feed on zooplankton, appears to be adapted for occasional herbivory. Such an adaptation is exceptional within a major ecological group of oceanic fishes that was previously thought to be exclusively carnivorous. Like omnivorous and herbivorous fishes in general, C. warmingii has a longer intestine than other myctophid species. As an adaptive response to competition from a diverse fish fauna in a low-productivity environment, occasional herbivory by C. warmingii runs counter to the theoretical expectation by expanding rather than narrowing the range of potential food types.     

Ultraviolet-based female preferences in a viviparous fish

Studies on fish have demonstrated female-mating preferences based on dimorphic colours and colour patterns, but commonly focused on the 400-700 nm (visible) band. In experiment 1 we exposed females of the amarillo (Girardinichthys multiradiatus), a viviparous fish with visually based female mate choice, to two views of males either containing (UV+) or lacking (UV-) information in the 300-400 nm region. Experiments were conducted outdoors, and we found that females spent more time next to the male seen through the UV+ filter than the same seen through the UV- filter. Since the two images only differed in the content of UV radiation, we conclude that females of the amarillo can detect UV light. Experiments 2 and 3 were designed to test whether such an effect can be attributed to female preferences based on the males' UV-reflecting colour patterns. We first assessed which area(s) of the fish have UV-reflecting properties. Then, using an opaque gelatine powder to block skin reflectance, we found that, in the presence of environmental UV light, females spend more time close to the males with powder sprinkled outside the UV-reflecting area (control) than to the males with powder sprinkled over the UV-reflecting area (experiment 2). This could have been due to the concealment of signals in the visible spectrum, rather than in the UV spectrum; thus we repeated the same experiment indoors, in the absence of UV light (experiment 2b); here females failed to discriminate between males. Since we also found that females have UV-reflecting areas in their flanks, we conducted a third experiment to test whether the preferential association of females found in the first experiment was due to the tendency to school/associate with conspecifics, rather than to mate choice (experiment 3). We found no evidence of discrimination in this experiment. We conclude that the UV markings and vision in G. multiradiatus have a function in female mate choice. This is the first time that evidence has been found for the influence of UV for mate choice in fish.     

Respiration of the bathypelagic fish Cyclothone acclinidens

The respiration of 3 adult females of Cyclothone acclinidens was measured in situ. These numerically dominant fish of the meso- and bathypelagic zones were individually captured off southern California at a depth of 1300 m using a multiple-chambered slurp-gun respirometer operated from the submersible Alvin. Continuous oxygen consumption measurements of each fish were made at the capture depth for about 28 h, spanning an interval from late morning to the following mid-afternoon. Nocturnal rates of respiration of these fish were 3 to 5 times higher than diurnal rates, suggesting a daily thythm in this non-migratory midwater species. Environmental factors such as tides, light, and food could serve to synchronize the observed respiration fluctuation.     

Odd fish abandon mixed-species groups when threatened

Summary In a field experiment, two juvenile size classes of striped parrotfish (Scarus iserti), stoplight light parrotfish (Sparisoma viride), and ocean surgeonfish (Acanthurus bahianus) were threatened by a model of a common predator (the trumpetfish, Aulostomus maculatus) while alone and in mixedspecies groups of 3–100 members. Striped parrotfish, which usually consitute the majority of a group, used the groups for protection. Stopight parrotfish, present in very low numbers, hid in the coral. Individuals of both species left a group sooner if it had fewer conspecifics. Small surgeonfish sought protection in groups, while larger individuals too big to be consumed by the trumpetfish, swam away alone. These results may be explained by differences in the protection derived from mixed-species groups, and particularly, by the high predation risk suffered by odd individuals.     

Offshore distributional patterns of Hawaiian fish larvae

An analysis of ichthyoplankton samples based on relative abundance reveals pronounced inshore/offshore distributional gradients for most Hawaiian fish larvae. Larvae of pelagic bay species are found almost exclusively in semi-enclosed bays and estuaries. Larvae of pelagic neritic species are more or less uniformly distributed with distance from shore. The larvae of reef species with non-pelagic eggs are most abundant close to shore, while those of reef species with pelagic eggs are most abundant offshore. Finally, the larvae of offshore (primarily mesopelagic) species show no clear pattern but frequently occur in high numbers nearshore. Within any group, variation in pattern was often evident; for example, although Hawaiian fishes of both the families Labridae and Mullidae spawn pelagic eggs, larvae of the former had not peaked in abundance 12 km from shore while larvae of the latter had peaked between 0.5 and 2 km. Some larvae which occur offshore are highly specialized morphologically for a pelagic existence (e.g. Chaetodontidae, which is illustrated) while others are little modified (e.g. Labridae). These findings indicate ichthyoplankton surveys in tropical areas must sample offshore areas in addition to the inshore adult habitat to obtain a complete picture.Hawaii Institute of Marine Biology Contribution No. 484.     

Size-assorted fish shoals and the majority's choice

Similarity among group members may serve as a defence against visually hunting predators that preferentially attack individuals who are phenotypically different from the group majority. The presence of such odd individuals in an otherwise homogeneous group may, however, increase the vulnerability of the other group members as well. Individuals might thus be expected to form uniform groups in order to decrease predation risk, not only in trying to avoid being odd in a group, but also when attempting to avoid being accompanied by odd individuals. This hypothesis was tested with small and large three-spined sticklebacks, Gasterosteus aculeatus. Focal fish were offered the choice between a shoal consisting of conspecifics that were all similar in body length to the focal fish (matching shoal) and a shoal in which one or a few individuals differed in body length from the focal fish (non-matching shoal). In the control experiment, all individuals in the non-matching shoal differed in size from the focal fish. The control confirmed that individuals preferably joined the matching shoal when the alternative option was to be odd in another one. However, when the alternative for size-assortative shoaling was to belong to the majority in a mixed shoal, the shoal choice of individuals appeared on average to be random. Visual contact with a live pike, Esox lucius, did not affect the shoal choice pattern. Furthermore, despite the frequency-dependent nature of the oddity effect, varying the number of odd individuals in the non-matching shoal did not have a significant effect on individual's shoaling decisions. These results suggest that size-assortativeness in fish shoals is not a result of individuals avoiding being among the majority in a mixed group. Received: 2 September 1998 / Received in revised form: 12 May 1999 / Accepted: 29 May 1999