The pineal complex of the three-spined stickleback,Gasterosteus aculeatus L.

Summary The pineal complex of the three-spined stickleback (Gasterosteus aculeatus L.) was investigated by light and electron microscopy, as well as fluorescence histochemistry for demonstration of catecholamines and indolamines. The pineal complex of the stickleback consists of a pineal organ and a small parapineal organ situated on the left side of the pineal stalk. The pineal organ, including the entire stalk, is comprised mainly of ependymal-type interstitial cells and photoreceptor cells with well-developed outer segments. Both unmyelinated and myelinated nerve fibres are present in the pineal organ. Nerve tracts from the stalk enter the habenular and posterior commissures. A small bundle of nerve fibres connects the parapineal organ and the left habenular body. The presence of indolamines (5-HTP, 5-HT) was demonstrated in cell bodies of both the pineal body and the pineal stalk, and catecholaminergic nerve fibres surround the pineal complex.     

Schooling affects growth in the three-spined stickleback, Gasterosteus aculeatus

Three-spined stickleback fry (mean length 20 mm, mean weight 14 mg) were reared for 14 days alone and in groups of six in a constant per capita water volume. The fish originated from two habitats (rock-pools, sea) of different predation pressure. The fry were fed nauplii of Artemia and commercial aquarium fish food ad libitum. Specific growth rates of solitary and schooling fry differed and were also affected by their origin. The specific growth rates of solitary fry from the sea averaged 1.0% day⁻¹ (length) and 6.0% day⁻¹ (weight) and those of solitary rock-pool fry 1.1 and 6.7%, respectively. For group-reared fish the corresponding values were 1.2% (length) and 6.6% (weight), and 1.3% (length) and 7.6% (weight). The finding that schooling sticklebacks grow faster than solitary ones implies that grouping enhances fitness in stickleback fry under the conditions of our experiments.     

A three-spined stickleback, Gasterosteus aculeatus L. from the North Atlantic

An unusual occurrence of a three-spined stickleback, Gasterosteus aculeatus , is described from Ocean Weather Station India in the North-east Atlantic. Previous records of G. aculeatus caught well offshore are summarised and reasons for these occurrences are suggested. Mention is made of the possibility of sticklebacks breeding in the open ocean.     

Studies on the toxicity of cadmium to the three-spined stickleback Gasterosteus aculeatus L.

Cadmium was found to be lethal to sticklebacks at all concentrations from 100.0 to 0.001 mg Cd 1^–1, in water of 103–111 mg 1^–1 hardness as CaCO₃. The pattern of mortality as shown by the time-concentration curve suggests that toxicity is not due to a single mechanism but changes with concentration. Fish were found to accumulate cadmium, the whole body levels increasing from 0.90 μg/g fresh weight at 0.001 mg Cd 1^–1 exposure concentration to 51.0 μg/g at 100 mg Cd 1^–1. The concentration factor was shown to decrease with increasing exposure concentration from 0.51 at 100 mg Cd 1^–1 to 511 at 0.001 mg Cd 1^–1. The plerocercoid parasite Schistocephalus solidus in the host's perivisceral cavity contained less cadmium than the tissues of its host.     

Fecundity of the three-spined stickleback, Gasterosteus aculeatus (L.)

The number of eggs spawned by female three-spined sticklebacks Gasterosteus aculeatus (L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.     

Inheritance of vertebral number in the three-spined stickleback (Gasterosteus aculeatus)

Intraspecific variation in the number of vertebrae is taxonomically widespread, and both genetic and environmental factors are known to contribute to this variation. However, the relative importance of genetic versus environmental influences on variation in vertebral number has seldom been investigated with study designs that minimize bias due to non-additive genetic and maternal influences. We used a paternal half-sib design and animal model analysis to estimate heritability and causal components of variance in vertebral number in three-spined sticklebacks (Gasterosteus aculeatus). We found that both the number of vertebrae (h² = 0.36) and body size (h² = 0.42) were moderately heritable, whereas the influence of maternal effects was estimated to be negligible. While the number of vertebrae had a positive effect on body size, no evidence for a genetic correlation between body size and vertebral number was detected. However, there was a significant positive environmental correlation between these two traits. Our results support the generalization-in accordance with results from a review of heritability estimates for vertebral number in fish, reptiles and mammals-that the number of vertebrae appears to be moderately to highly heritable in a wide array of species. In the case of the three-spined stickleback, independent evolution of body size and number of vertebrae should be possible given the low genetic correlation between the two traits.     

Ultraviolet light and visual behaviour in the three-spined stickleback, Gasterosteus aculeatus

The ability of various vertebrates to perceive visual information in the ultraviolet region of the electromagnetic spectrum (300-400 nm) is receiving increasing interest. To date, many of these studies have concentrated on the role of ultraviolet perception in mate choice, yet there are several ways in which the ability to perceive ultraviolet information may affect other behaviours. Until now, it has been widely assumed that colour in the three-spined stickleback can be quantified by methods appropriate to the human visual system. However, evidence does exist that suggests that, in some populations, sticklebacks are capable of perceiving ultraviolet wavelengths. Using a behavioural technique, we tested the ability of the stickleback to perceive ultraviolet light under full-spectrum conditions to establish whether such wavelengths are utilised within their normal behavioural repertoire. We tested this ability by assessing whether subjects could locate hidden food in a foraging task where food position was indicated by the position of landmarks. These landmarks differed only in their ultraviolet content, appearing identical when viewed across the human visible region of the spectrum. We found that sticklebacks were able to use ultraviolet perception to locate a foraging patch under full-spectrum conditions.     

Dyadic relationships in nesting males of the three-spined stickleback, Gasterosteus aculeatus

Multidimensional scaling analysis of nest site location, nesting interval, and aggressive and mating interactions revealed that male three-spined sticklebacks, Gasterosteus aculeatus, formed nesting clusters comprising five patterns of dyadic relationships. These patterns were defined by intervening variables such as size difference between the two males, nest site locations, synchronization of nesting cycles (egg presence in the nest), distance between two nests, and nest raiding behaviours. Several patterns of dyadic relationships were integrated among nesting males and their constellations indicated an expression of the social structure. Through an understanding the social structure, I described effects of social context or situations on individual reproductive success.     

Daily growth increments in the otoliths of the three-spined stickleback, Gasterosteus aculeatus L.

Daily increment formation was demonstrated in the sagittae of the three-spined stickleback, Gasterosieus aculeatus L., under both laboratory and field conditions. The onset of daily increment formation coincided with the day of hatching. The main sources of inaccuracy in age determination resulted from difficulties in resolving narrow increments in the sagittae of fish held at low temperatures and the increasing incidence of checks with age. The advantage of daily increments for investigating growth in this species was demonstrated from a comparison between increment-derived age-at-length data and length-at-capture data, since the latter significantly under-estimated early growth rate within a population.     

Cost of egg production in the three-spined stickleback (Gasterosteus aculeatus L.)

In the interval between successive spawnings, female sticklebacks consumed approximately their own wet weight of Tubifex. On average, for 100 cal of food consumed, 26 cal of eggs, 3 cal of somatic growth and 11 cal of faeces were produced. In the absence of somatic growth, the efficiency of egg production was estimated as nearly 30%, and it was predicted that in the absence of egg production, the efficiency of somatic growth would range from 20% for a fish of 0.8 g wet weight to 3% for 2 g fish.
The weight of eggs produced at a spawning was a function of the weight of the female but not of the amount of food consumed. If food consumption was not sufficient to cover the cost of egg production, the fish lost weight. Total production (the summation of egg production and somatic growth) was a function of the amount of food consumed.     

Genetic evidence for male-biased dispersal in the three-spined stickleback (Gasterosteus aculeatus)

Sex-biased dispersal is capable of generating population structure in nonisolated populations and may affect adaptation processes when selective conditions differ among populations. Intrasexual competition for local resources and/or mating opportunities predicts a male-biased dispersal in polygynous species and a female bias in monogamous species. The patterns of sex-biased dispersal in birds and mammals are well explained by their respective mating systems, but the picture emerging from fish studies is still mixed. Using neutral genetic markers, we investigated whether there is any evidence for sex-biased dispersal among Baltic Sea populations of the three-spined stickleback ( Gasterosteus aculeatus ). The null hypothesis of non sex-biased dispersal was rejected in favour of male-biased dispersal in this species. As the three-spined stickleback has a polygynous mating system, the observed male bias in dispersal is consistent with the hypothesis that local mate competition might drive the observed pattern. Although more research both on the proximate and ultimate causes behind the observed pattern is needed, our results serve as a first step towards understanding patterns of sex-biased dispersal in this species.     

The effect of parasitism on the toxicity of cadmium to the three-spined stickleback, Gasterosteus aculeatus L.

The toxicity of cadmium to sticklebacks was determined over a wide range of concentrations. The 96 h LC50 was found to be 6.5 mg Cd I⁻¹. The shape of the time-concentration curve suggests that cadmium may have two toxic mechanisms. The median period of survival for fish infected with the plerocercoids of the cestode, Schistocephalus solidus , was found to be considerably shorter than for non-parasitized fish. This observation is considered in the light of the known effects of 5. solidus on its host.     

The effect of ration and temperature on the growth of the three-spined stickleback, Gasterosteus aculeatus L.

The effect of ration on the growth of the three-spined stickleback, Gasterosteus aculeatus , was studied over the temperature range 3·19°C, which corresponded to the range in their natural habitat. With an ad lib ration, the specific growth rate increased with temperature. The relationship between specific growth rate and ration at a given temperature was curvilinear. Regression models were used to predict the maximum, optimum and maintenance rations at each temperature. Whereas maximum ration increased rapidly with temperature, the optimum and maintenance rations were relatively insensitive to temperature. A regression model was used to describe the overall relationship between specific growth rate and ration, temperature and body weight. This model predicted that at low rations, growth rate decreased with temperature, whereas at high rations, growth rate increased slightly with temperature. The gross growth efficiency increased rapidly with rations above maintenance ration up to a maximum at the optimum ration and declined at higher rations. The maximum gross growth efficiencies were at high temperatures and rations about half of the maximum ration. The maximum net growth efficiencies occurred at relatively low temperature and at rations just above maintenance.     

Serotonin and opsin immunoreactivities in the developing pineal organ of the three-spined stickleback,Gasterosteus aculeatus L.

Summary Macrophages of the adrenal cortex were studied in normal male and female, ovariectomized and estradiol-injected rats. In normal male rats few macrophages with numerous granules were observed in the zona fasciculatazona reticularis border, and in the zona reticularis. Granules, identified as lysosomes, were limited by a single membrane with a heterogeneous matrix; they exhibited acid phosphatase- and aminotriazole-resistant peroxidatic activities. A larger number of macrophages had identical distributions in normal female rats. In ovariectomized and estradiol-injected rats the number and distribution of adrenal macrophages were similar to those in normal females; however, in spayed animals the number of these cells in the zona reticularis was higher than in the other experimental groups. Lysosomes in macrophages of treated animals were more numerous and their contents more complex than in normal male animals. These results indicate that the adrenal macrophage system is stimulated in experimental conditions involving high levels of circulating estrogens.     

Production of the three-spined stickleback, Gasterosteus aculeatus L., in the River Weaver, England

1. The production of three-spined sticklebacks, Gasterosteus aculeatus , estimated in the margin of a large channelized lowland river, averaged 42.3 g m⁻² yr⁻¹ and the P/B ratio was 3.7. The production value greatly exceeds those previously recorded for G. aculeatus and results from the very high population densities.
2. Life-bistory tactics of the sticklebacks included both r- and K-selected traits.
3. The fish were carnivorous in the summer months but predominantly detritivorous in the winter.     

Migratory history of the threespine stickleback Gasterosteus aculeatus

 The migratory history of two highly divergent forms (the Japan Sea and Pacific Ocean forms) of the threespine stickleback Gasterosteus aculeatus collected from Japanese brackish water (seawater) and freshwater was studied by examining strontium (Sr) and calcium (Ca) concentrations in their otoliths using wavelength dispersive X-ray spectrometry on an electron microprobe. The Sr : Ca ratios in the otoliths changed with salinity of the habitat. The otolith Sr : Ca ratios of the freshwater resident-type samples of the Pacific Ocean form showed consistently low Sr : Ca ratios, averaging 0.85–0.96 × 10⁻³ from the core to the edge. In contrast, the otolith Sr : Ca ratios of the anadromous type of both the Japan Sea and Pacific Ocean forms fluctuated strongly along the life history transects in accordance with their migration patterns from seawater to freshwater. The higher ratios in the anadromous type, averaging 5.4 × 10⁻³, in the otolith region from the core to 200 μm, corresponded to the seagoing period, suggesting that otolith Sr : Ca ratios are affected by ambient water salinity. These findings clearly indicate that otolith Sr : Ca ratios reflect individual life histories, and that these two highly divergent forms of stickleback have a flexible migration strategy. Received: May 23, 2002 / Revised: July 29, 2002 / Accepted: August 19, 2002 Acknowledgments We are grateful to Dr. S. Mori of Gifu Keizai University, and Miss M. Yamada and Messrs. M. Kume and T. Kitamura of Hokkaido University, for their assistance in sampling. This work was supported in part by Grant-in-Aid No. 13760138 from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Correspondence to:Takaomi Arai