Effects of salinity on strontium:calcium ratios in the otoliths of the West African black-chinned tilapia Sarotherodon melanotheron in a hypersaline estuary

The biology and the behaviour of fish populations in hypersaline environments are poorly known. The habitat occupation strategy of the tilapia Sarotherodon melanotheron has been studied along a salinity gradient in the Saloum hypersaline estuary in Senegal (salinity between 32 and 100). The individual migratory behaviour has been analysed from otolith strontium-to-calcium concentration ratios from fish sampled in five locations during the 2003 wet season and the 2004 dry season. In the upper part of the estuary (salinities > 50), the Sr:Ca ratio in the otolith showed high variations, from 2.51 to 33.30 × 10⁻³. These maximum observed values have never been reported in the literature. The individual mean of Sr:Ca ratios increased according to the salinity gradient in the estuary, with significantly higher values in the upper part (Sr:Ca mean = 16 × 10⁻³) than in the lower part (salinity < 50, Sr:Ca mean = 12 × 10⁻³). No significant difference in the Sr:Ca mean was observed between locations with comparable salinities. Sr concentration in the water at the different locations was positively correlated with ambient salinity. The mean of Sr:Ca in the otoliths was then in relationship with the level of Sr in the water. Thus, the Sr:Ca ratios in the otolith of S. melanotheron allowed to discriminate the populations of this species and to hypothesize that they did not undertake large scale movements within the estuary.     

Does fragmented river connectivity alter the reproductive behavior of the potamodromous fish Alburnus vistonicus?

Blocked riverine spawning migration routes constitute one of the main threats of potamodromous fish that require well-connected habitats of high quality to maintain their unique life-history form. Alburnus vistonicus, a potamodromous species inhabiting the Vistonis freshwater system in northern Greece, manages to cope with wide salinity fluctuations in Vistonis Lake, but the impact of the fragmented connectivity of the lake’s two main freshwater suppliers, Kosynthos and Kompsatos rivers, has not been assessed. We analyzed the species whole reproductive cycle and we divided it into phases. Cyclicity was observed in gonadosomatic index and oocyte diameter, while total fecundity remained constant prior to the onset of the spawning season. Stomach fullness and condition factor differed among the surveyed habitats. Successful spawning and multiple spawning were verified, as well as spawning migration and potamodromy. However, mature females with markers of recent spawning activity were captured also in the lake, suggesting spawning occurrence in the lake or a previously undocumented oscillatory behavior between the lake and the rivers during the spawning season and between sequential spawning events. Either behavior may serve as a mechanism to overcome the restricted spawning migration routes due to the fragmented river connectivity.

     

Effect of seawater temperature on reproductive seasonality and fecundity of Pseudoplexaura porosa (Cnidaria: Octocorallia): latitudinal variation in Caribbean gorgonian reproduction

Abstract. The majority of tagged colonies of Pseudoplexaura porosa in Bermuda were reproductive over 2 months in the summer. They spawned 5–8 d after the full moon, with a peak on the sixth day, similar to colonies in Panama. The months of spawning were August and September in 1998, but July and August in 1999 and 2000. This temporal difference between the months of spawning corresponded to inter-annual variations in seawater temperature profiles. Initial gamete development each year occurred only when the daily mean seawater temperature during the month before spawning exceeded 27°C. There was a significant positive relationship between reproductive effort (gamete volume) of colonies and rising seawater temperature in the month preceding spawning; this was true for both the initial and the second spawning months. The end of the reproductive season each year was triggered by the decline in seawater temperature past the summer maximum. The duration of the reproductive season of conspecifics at the central Caribbean reef of Panama is 2 months longer than in Bermuda. This can be explained by the smaller annual temperature range at the lower latitude and the earlier onset of temperatures favorable for gamete development. Fecundity estimates for members of P. porosa (mean oocyte and spermary densities) in Bermuda were lower than for conspecifics in Panama. The shorter reproductive season in Bermuda, in addition to the lower fecundity of colonies, indicates that reproduction in P. porosa is compromised at this high latitude reef.     

Variation in gene expression along a salinity gradient in wild populations of the euryhaline black-chinned tilapia Sarotherodon melanotheron

This study evaluated variation in expression of 11 genes within and among six wild populations of the black-chinned tilapia Sarotherodon melanotheron distributed along a salinity gradient from 0 to 100. Previous laboratory studies had shown that expression of these genes was sensitive to water salinity; the current study confirmed that a number of them also varied in expression in wild populations along the salinity gradient. Principal component analysis (PCA) first distinguished two, not mutually exclusive, sets of genes: trade-off genes that were highly expressed at one or other extreme of the salinity gradient and stress genes that were up-regulated at the two salinity extremes (i.e. a U-shaped expression pattern). The PCA clearly partitioned the populations into three groups based on their gene expression patterns and their position along the salinity gradient: a freshwater (GL; 0) population, four brackish and seawater (GB, HB, SM, SF; ranging from 20 to 50) populations and a hypersaline (SK, 100) population. Individual variation in gene expression was significantly greater within the populations at the extreme compared to intermediate salinities. These results reveal phenotypically plastic regulation of gene expression in S. melanotheron, and greater osmoregulatory and plasticity costs at extreme salinities, where fitness-related traits are known to be altered.     

Influence of salinity on the size at maturity for fish species reproducing in contrasting West African estuaries

The influence of salinity on life-history traits was tested using two adjoining West African estuaries: the Gambia with a 'normal' salinity gradient (salinity always <40 and decreasing from the mouth upstream) and the Sine Saloum (Senegal) with an inverse gradient (from 35 at the estuary mouth up to >130 in the upper reaches). The breeding seasons and subsequent fork length ( L _F) at first maturity ( L _F50) were estimated for different fish species reproducing both in the Sine Saloum and in the Gambia River estuaries using a database built from experimental fish samplings between 1990 and 2003 with a purse seine (30 locations in the Sine Saloum and 44 in the Gambia). The database contained 30 553 individuals belonging to 60 different species among which only 20 species reproduced in both estuaries. The breeding seasons peaked just before, or at the beginning of the rainy season (June to July), and there were almost no sexually mature fishes at the beginning of the dry season (November to December). Patterns of differences between L _F50 of the two estuaries did not follow a general trend (positive or negative), but varied in the same way for females and males of a given species. The L _F50 was only systematically reduced with increasing salinity in species living in high-salinity waters (>70). For species living below 70, differences in sizes at first maturity between the two estuaries did not show any clear relationship with salinity. The smallest mature individual found in an environment was a good indicator of the size at first maturity reached in a particular ecosystem because the trend of the species differences between the two ecosystems generally followed that of the differences in size at maturity.     

Reproductive strategy of Psectrogaster rhomboides Eigenmann & Eigenmann, 1889, a freshwater fish from Northeastern Brazil

Several environmental parameters related to the spawning season of the freshwater fish, Psectrogaster rhomboides were identified. The hypothesis predicts synchrony of the spawning season with the rainy period, presenting a seasonal reproductive strategy. This study investigated the total body length and body mass, sex ratio, body size at first sexual maturity, gonadosomatic index, condition factor, fecundity and reproductive period of P. rhomboides in the natural environment. Twelve monthly samplings (mean n = 20) were carried out from March 2009 to February 2010. Fish were captured using 4 cm diameter cast nets and environmental parameters such as rainfall, temperature, dissolved oxygen concentration, pH and electrical conductivity of the water were registered. The sampled population of P. rhomboides (n = 444) showed a sex ratio of 1 : 1. Females attained first sexual maturity at 15 cm total length and males at 15.3 cm total length. Spawning occurred from March to May, with high gonadosomatic index values during the rainy season. This species is a total spawner, with a mean fecundity of 6188 (±367) mature oocytes. P. rhomboides presents a seasonal reproductive strategy, providing a population increase and exploitation of the environmental resources during the rainy period. Rainfall (196.5 ± 4.9 mm) and the concentration of dissolved oxygen (7.82 ± 0.7018 mg L^?1) were influential factors during the spawning season. Gonadosomatic index and the condition factor were negatively correlated during the gonadal development cycle of this species. The monthly gonadosomatic index values show that spawning begins when the rainy season is at its maximum and ends synchronously (females r = 0.9171; males r = 0.889) with the end of the rainy season.     

The impact of environmental degradation on reproduction of the black-chinned tilapia Sarotherodon melanotheron from various coastal marine,estuarine and freshwater habitats

There is growing evidence that climate change has greatly altered environmental conditions in many aquatic ecosystems over the last decades, leading to changes in fish distribution and life history traits. Recent works conducted in Senegalese and Gambian coastal marine, estuarine and freshwater ecosystems have shown important changes in the intensity, frequency and breeding timing of wild population of Sarotherodon melanotheron in response to changes in salinity regimes. In addition to salinity, this study investigates the potential influences of other environmental factors that have received less attention on the reproduction of S. melanotheron from three different aquatic ecosystems in Senegal. The results demonstrate that day-length and temperature affect sexual maturity in both males and females from Guiers Lake and Hann Bay, but no such effects were found in upstream of the Saloum Estuary, where the spawning activity seems to be under the synergetic control of rainfall and salinity that apparently predominate over all the other ambient factors. This study demonstrated for the first time that aside from photoperiod and temperature, rainfall also influences fish reproduction in Hann Bay probably through its effects on water quality. Furthermore, our results confirm previous findings that changes in salinity regimes resulting from seasonal variations in precipitation and evaporation are the ultimate causes of temporal changes in the reproductive activity of the species in this estuary.     

Reproduction mode of European Bitterling (Rhodeus amarus,Bloch, 1782) determined through rapid oocyte counts and size determination using digital imaging

This study focuses on assessing the reproduction mode of an important model species for evolutionary and behavioural ecology by using digital image analysis: the European bitterling Rhodeus amarus (Bloch, 1782). Specifications of mode of reproduction were determined using oocyte size distribution, seasonal dynamics in mean oocyte diameter and total number of oocytes in ovary samples gained from April to July 2007. The rapid oocyte count was enabled by using lucia image analysis software, which also provided measurement and colour estimations of oocytes. Bitterling ovaries showed features typical for indeterminate spawners, i.e. a continuous distribution of oocyte size over the reproductive season and recruitment of new pre‐vitelogenic oocytes in the second half of the reproductive season. These results are consistent with the view that the European bitterling is a batch spawning fish with indeterminate fecundity.     

Comparative study of sexual cycles, oogenesis and spawning of two Soleidae, Solea lascaris (Risso, 1810) and Solea impar (Bennet, 1831), on the western coast of Brittany

Two sand sole species, Solea lascaris and Solea impar , are common on the western coast of Brittany, France. Their reproduction (oogenesis and spawning) has been studied by following the gonadosomatic index, histological changes in ovary development, and oocyte diameter distribution. Both species have a prolonged spawning season, from spring to late summer. Each mature female breeds twice during the spawning season: in May and July for 5. lascaris , and in early June and July for 5. impar. Throughout the spawning season, several oocyte batches undergo vitellogenesis and there is a continuous recruitment of immature or primary oocytes into vitellogenesis. The two species are thus serial synchronous spawners. This, together with oocyte atresia late in the season (especially noticeable in S. impar ) makes fecundity estimation difficult.     

Reproductive strategy of Leporinus piau (Fowler, 1941), a neotropical freshwater fish from the semi‐arid region of Brazil

This study concerns the reproductive strategy of the freshwater fish, Leporinus piau, native to the Brazilian semi‐arid region. The hypothesis of this work predicts that the species would spawn during the rainy season, presenting a seasonal reproductive strategy. The study investigated the structure of total body length and body mass, sex ratio, body size at first sexual maturity, developmental stages of gonads, fecundity, gonadosomatic index (GSI), condition factor (K) and the spawning season of L. piau. Twelve monthly samplings (mean n = 18) were carried out in 2009 and environmental parameters such as rainfall, temperature, pH, electrical conductivity and concentration of dissolved oxygen of water were registered. The sampled population of L. piau (n = 211) showed a slight predominance of males (55%), but with larger and heavier females. First sexual maturation in males occurred earlier (16.5 cm total length) than in females (20.5 cm total length). The species is a total spawner with an average fecundity of 55 000 mature oocytes. Rainfall (225 ± 7.2 mm) and concentration of dissolved oxygen (8.5 ± 0.2 mg L^?1) acted as influential factors during the spawning season. The monthly GSI shows that spawning starts when the rainy season is at its maximum and ends synchronously (females r = 0.91; males r = 0.89) with the end of the rainy season. L. piau presents a seasonal reproductive strategy with high reproductive output, providing a population increase and exploitation of the environmental resources.     

Hypersalinity effects on leaf ultrastructure and physiology in the mangrove Avicennia marina

The effects of hypersalinity on leaf ultrastructure and physiology in the mangrove, Avicennia marina, were investigated by comparing leaves of adult trees growing naturally in the field under seawater and hypersalinity conditions in Richards Bay, South Africa. We tested the hypothesis that hypersalinity has a deleterious effect on membranes and cellular organelles such as chloroplasts and mitochondria, which would impact negatively physiological processes, such as ion and water relations, and photosynthetic performance. Soil ψ and soil salinity were −2.96 ± 0.07 MPa and 35 ± 2.8 psu in the seawater salinity site, compared to −5.91 ± 0.42 MPa and 58 ± 3.6 psu respectively, in the hypersaline site. In the hypersaline site, leaves were smaller and thicker, with thicker cuticles, while chloroplasts, mitochondria and nuclei exhibited swelling and disintegration, compared to those at seawater salinity. Multivesicular structures and vesicles, observed in vacuoles, chloroplasts, mitochondria, and along cell walls and plasma membranes, were more abundant in leaves from the hypersaline than the seawater site, and were probably indicative of greater plant salt uptake in the former site. Leaf concentrations of total chlorophyll and chlorophylls a and b were lower in trees from the hypersaline site by 33%, 29%, and 45% respectively, compared to those at seawater salinity. Midday minimum xylem ψ was −3.82 ± 0.33 MPa in the seawater site and −6.47 ± 0.45 MPa in the hypersaline site. In the hypersaline site, the concentration of leaf Na⁺ was 40% higher, while those of K⁺, Ca²⁺, and Mg²⁺ were lower by 45%, 44%, and 54% respectively, than those in the seawater site. CO₂ exchange and the intrinsic photochemical efficiency of PS II were significantly lower in trees from the hypersaline site by 48 and 19% respectively. The ultrastructural evidence supported the physiological data that A. marina trees in the hypersaline site are under extreme salinity stress and that this species is growing there at the upper limit of its salt tolerance.     

Reproductive traits of the “ocellated killifish” Floridichthys polyommus Hubbs, 1936 (Pisces: Cyprinodontidae) inhabiting estuary of the Champotón River (Campeche,Mexico)

This study explores the reproductive biology and the influence of environmental factors on the reproductive traits of Floridichthys polyommus inhabiting the estuary of the Champoton River. The analysis included population structure, gonadal developmental stages, reproductive period, size at first sexual maturity, fecundity, sex ratio, and somatic indexes. A spatio‐temporal pattern in the distribution of the seven size classes was detected. The species showed a positive allometric growth. Sex ratio was 1.21:1 (females:males). Size at first maturity was 42.23 mm (females) and 47.8 mm (males). A higher absolute and relative fecundity was detected in Puente Champotón estuary (PCH) with lower salinities than those detected in the Delta (DE). The adaptive significance of this trait could be in response to the heavy osmotic constraint imposed by extreme salinities in the DE. Floridichthys polyommus prefers PCH for spawning, and as a result a higher number of ripe individuals was observed in this site, characterized by the highest nutrient levels, which can boost productivity and food availability for fish. Hepatosomatic index was negatively correlated with gonadosomatic index, suggesting energy transfer from the liver towards gamete production. Floridichthys polyommus exhibits an opportunistic strategy (early maturity, small oocytes, small clutches) suggesting that energy is allocated towards reproduction to compensate for the unpredictable hydrological conditions imposed by the estuary (particularly during the hurricane season). Floridichthys polyommus shows a reproductive strategy exhibited by fish living in unstable systems. A seasonal divergence was observed in the reproductive traits of F. polyommus, while differences between study sites were for fecundity.     

Reproductive biology ofAwaous guamensis, an amphidromous Hawaiian goby

Synopsis Spawning season, size at first reproduction, oocyte maturation, and fecundity ofAwaous guamensis, an amphidromous Hawaiian goby, were studied from June 1989 through May 1991 in the Wainiha River, Kau'ai, Hawai'i. Female fish larger than 73 mm standard length (SL) had mature gonads from August through December in 1989 and 1990. Gonadosomatic index (GSI) values for mature females ranged from 0.2 to 14.5 during the spawning season. Male fish larger than 64 mm SL had elevated GSI values from June 1989 through December 1989 and from August 1990 through December 1990. Mature sperm were found in two male fish collected in January and February. GSI values for mature males ranged from less than 0.01 to 4.0 in the spawning season. Size-frequency distributions of measurements of vitellogenic oocyte diameters and microscopic observations of oocytes indicated this species has group-synchronous oocyte development. Ovarian maturation stages examined over a 29-month period suggest that members of the stock spawned at different times within the spawning season, although mass spawning events have been documented for this species. Estimates of clutch sizes from nests measured in situ were comparable to estimates of potential fecundity from in vitro examination of ovaries, and indicated that female fish deposited an entire clutch during a spawning event. No evidence for multiple spawning by an individual fish in a single season was found. However, microscopic observations of brown bodies in some ovaries suggested that individual fish probably spawn more than once in a lifetime.     

Osmoregulatory strategies in natural populations of the black-chinned tilapia Sarotherodon melanotheron exposed to extreme salinities in West African estuaries

The effect of salinity was studied in natural populations of the black-chinned tilapia (Sarotherodon melanotheron) from West Africa. This euryhaline species colonizes nearly all coastal environments from bays to lagoons characterized by salinities ranging from fresh water to hypersaline water over 100 ‰. Individuals were sampled during the dry season at several locations characterized by different levels of salinity (3-102 ‰). Their osmotic status and their gills were analyzed. The branchial mitochondria-rich cells (MRC), localized at the basis of the filaments and along the lamellae in fish taken from the saline stations, showed a wide plasticity with significant differences in their number and size. The most striking results were a significant larger area (≈3x) and a higher number (≈55x) of MRC at high salinity (102 ‰) compared to low salinity (3 ‰). The major ion transporters and channels were localized by immunocytochemistry and different expression patterns have been recorded between stations. Despite an increased Na?/K?-ATPase (NKA) α-subunit expression and NKA activity, pointing to an increased monovalent ion excretion, a severe osmotic imbalance was recorded in animals living in hypersaline environments.     

Coral reproduction in the world��s warmest reefs: southern Persian Gulf (Dubai, United Arab Emirates)

Despite extensive research on coral reproduction from numerous geographic locations, there remains limited knowledge within the Persian Gulf. Given that corals in the Persian Gulf exist in one of the most stressful environments for reef corals, with annual variations in sea surface temperature (SST) of 12°C and maximum summer mean SSTs of 36°C, understanding coral reproductive biology in the Gulf may provide clues as to how corals may cope with global warming. In this study, we examined six locally common coral species on two shallow reef sites in Dubai, United Arab Emirates (UAE), in 2008 and 2009 to investigate the patterns of reproduction, in particular the timing and synchrony of spawning. In total, 71% colonies in April 2008 and 63% colonies in April 2009 contained mature oocytes. However, the presence of mature gametes in May indicated that spawning was potentially split between April and May in all species. These results demonstrate that coral reproduction patterns within this region are highly seasonal and that multi-species spawning synchrony is highly probable. Acropora downingi, Cyphastrea microphthalma and Platygyra daedalea were all hermaphroditic broadcast spawners with a single annual gametogenic cycle. Furthermore, fecundity and mature oocyte sizes were comparable to those in other regions. We conclude that the reproductive biology of corals in the southern Persian Gulf is similar to other regions, indicating that these species have adapted to the extreme environmental conditions in the southern Persian Gulf.     

Embryonic encapsulation and maternal incubation: Requirements for survival of the early stages of the estuarine gastropod Crepipatella dilatata

During their reproductive period, females of Crepipatella dilatata deposit their embryos in capsules that they then brood in the pallial cavity until juveniles emerge several weeks later, after passing through a transient veliger “larval” stage. Artificially excapsulated veligers of this species experimentally exposed to a wide range of salinities (5, 10, 15, 20, 25, and 30 psu) for six hours showed reduced activity at salinities of 15 and 20 psu, whereas encapsulated veligers exposed to those same salinities showed no reduction of activity. Artificially excapsulated veligers showed high mortality at salinities of 5 and 10 psu; encapsulated embryonic stages also showed high mortalities at 5 psu and serious sublethal effects at 10 psu in tests excluding maternal protection, showing that encapsulation alone does not provide complete protection from low salinity stress. Natural tidal cycles in the Quempillén River estuary also reduced embryonic survival at salinities of ≤ 10 psu when the capsules were exposed without maternal protection. In contrast, encapsulated embryos protected by their mothers survived well regardless of the salinity to which they were exposed, under both natural and laboratory-simulated estuarine tidal cycles. C. dilatata are able to develop in the estuary only because of maternal protection, since salinity levels in this environment sometimes decline to as low as 7 psu. Successful embryonic development in this estuary reflects the capacity of C. dilatata adults to detect dangerously low salinity levels and then seal themselves off from the environment for up to 50 hrs (O. Chaparro pers. obs.) when the salinity drops below 22.5 psu, allowing salinity to remain above this level within the pallial cavity despite continued salinity declines in the surrounding seawater.     

Reproductive Timing of Fishes in a Tropical Intermittent Stream

Six fish species were studied in an intermittent lowland stream in Trinidad, West Indies for 28 months from 1980 to 1982. They were Gasteropelecus sternicla, Corynopoma riisei, Astyanax bimaculatus, Hemigrammus unilineatus, Corydoras aeneus and Poecilia reticulata. Peaks in GSIs and presence of mature adults and juveniles, as determined from monthly field collections, indicated reproduction coincident with the rainy seasons in all species except Poecilia. Gasteropelecus bred for a short period at the beginning of the main rainy season while Corynopoma, Corydoras and Hemigrammus had extended periods of breeding activity each year coincident with high rainfall. The presence of juveniles suggests that Astyanax also bred during the rainy season. Poecilia reproduced continuously throughout the study period but exhibited discharge-related adult stock fluctuations that may have influenced reproductive activity. Maximum ovarian fecundity correlated with species size suggested body size limitation on fecundity for small species such as Corynopoma and Hemigrammus. Size frequency distributions of oocytes in mature ovaries indicate synchronised ovum maturation in Astyanax and possibly Gasteropelecus, while Hemigrammus, Corynopoma and Corydoras showed evidence of continuous maturation of oocytes and multiple spawning. Prolonged small brood spawning was confirmed in the laboratory for Corynopoma and Hemigrammus and resulted in spawning fecundities up to 11 times greater than ovarian fecundities for Corynopoma. It is concluded that the conditions of intermittency in this stream did not significantly alter the reproductive styles of these species as described for other Neotropical environments, perhaps because of their opportunistic nature. Patterns of spawning for the characoids can be directly related to size and phylogeny.     

Impact of environmental DDT concentrations on gill adaptation to increased salinity in the tilapia Sarotherodon melanotheron

Estuaries of tropical developing countries suffering from severe droughts induced by climate change are habitats to fish, which face drastic salinity variations and the contact with pollutants. The Western Africa tilapia Sarotherodon melanotheron is highly resistant to hypersalinity, but the effect of human-released xenobiotics on its adaptation is barely known. Controlled experiments were conducted to observe S. melanotheron gill adaptation to abrupt salinity variations in the presence of waterborne DDT, at concentrations detected in their natural habitat. The gills appeared as an important site of DDT conversion to DDD and/or depuration. A 12-days DDT exposure resulted in decreased gill epithelium thickness at all salinities (from fresh- to hypersaline-water), and the structure of gills from freshwater fish was particularly altered, relative to controls. No unbalance in tilapia blood osmolality was observed following DDT exposure, which however caused a decrease in branchial Na(+)-K(+)-ATPase (NKA) activity. Gill cellular NKA expression was reduced in salt-water, together with the expression of the CFTR chloride channel in hypersaline water. Although S. melanotheron seems very resistant (especially in seawater) to short-term waterborne DDT contamination, the resulting alterations of the gill tissue, cells and enzymes might affect longer term respiration, toxicant depuration and/or osmoregulation in highly fluctuating salinities.     

Reproductive ecology of Brazilian freshwater fishes

We used metadata on nine reproductive traits of 67 species of Brazilian iteroparous, oviparous, teleost freshwater fishes to test phenotypes associations to discriminate species that only spawn in large rivers (lotic fishes) from those capable to spawn in lentic habitats (lentic fishes). We tested the hypothesis that lotic fishes present spawning migration, shorter spawning season, single spawning, no parental care, free eggs, higher relative fecundity, faster embryogenesis, and larger size, while lentic fishes present no spawning migration, longer spawning season, multiple spawning, parental care, adhesive eggs, lower relative fecundity, slower embryogenesis, and smaller size. Our analyses supported the hypothesis but not all phenotypic associations satisfied it, specifically with regard to lentic fishes or to pairs of phenotypes typical of lentic fishes. We also concluded that spawning in large rivers is a better predictor of bionomic characters than spawning in lentic habitats, and lotic fishes are specialists compared to lentic fishes.     

Reproduction of Joturus pichardi and Agonostomus monticola (Mugiliformes: Mugilidae) in rivers of the Sierra Nevada de Santa Marta, Colombia

The freshwater mugilids Joturus pichardi and Agonostomus monticola, have been documented on ecological and distribution aspects, mainly for Central American populations, nevertheless, little information is available on their reproductive aspects, specifically in Colombian freshwater environments. Reproductive biology of the mugilids J. pichardi and A. monticola from Sierra Nevada de Santa Marta (SNSM) rivers was studied between July 2005 and December 2006. A total of 14 specimens of J. pichardi and 320 of A. monticola were collected. The reproductive biology was analyzed by means of: sexual proportion, gonadosomatic index, and mean size at maturity, fecundity and oocyte diameter. Additionally, a bioassay was carried out to evaluate the effect of salinity on spermatic motility and its possible relationship with the species' spawning area. These mugilids share habitats with similar ecological characteristics, in which strong currents; clear water and stony areas stand out. Gonadal maturity indicators and indirect evidence are presented to support the relationship between reproductive maturity and higher rainfall levels in the area (September, October and November), as well as the catadromous migration of J. pichardi and A. monticola. This last species females outnumbered males with a sex ratio of 2.3:1. Females mean size at maturity was 172mm of their total length (TL) and 108mm TL for males. Fecundity (F) was 23 925 +/- 4 581 eggs per gram of gonad, and was related to size by the equation F = 395.1TL(1.281); besides, the mean oocyte diameter was 362 +/- 40 microm. Considering the salinity effect on sperm motility in both species, results suggested that J. pichardi spawned in estuarine environments but the species did not migrate to fully marine environments; however, A. monticola withstood a broad range of salinity, suggesting a spawning from intermediate to total saline environments. Both species have high culturing potentials, considering that their feeding is based on plant and macroinvertebrates, their meat quality and the size they are able to reach. These species represent an interesting resource to the fisher groups of the region and should be integrally assessed.