A bioenergetics model for an air-breathing fish, Channa striatus

Food consumption, standard metabolism, and growth of juvenile snakehead, Channa striatus, a cannibalistic and air-breathing fish were measured at 24–26 °C under controlled laboratory condition. Snakehead weighing 3.2–29.5 g were evaluated, and were fed smaller snakehead. Based on our observations, we determined bioenergetics relationships between specific food consumption, metabolic rates, and body weight. These values, along with other published parameter values allowed us to construct a bioenergetics model for snakehead. We then verified our model with growth and food consumption measurements from an independent feeding trial. Predicted fish growth closely matched observed growth. Our model underestimated cumulative food consumption when a constant activity value was used, but consumption estimates improved when we used non-constant activity values (1-5 times of standard metabolism). Predicted fish maintenance ration was 1.7% of body weight per day. Food conversion efficiency was greatest (0.59) when fed 2% body weight daily, but declined when daily consumption exceeded 6% body weight. This model provides a useful approach for assessing food requirements of snakehead under controlled condition. This revised version was published online in July 2006 with corrections to the Cover Date.     

汉江中下游水文特点与渔业资源状况

通过对汉江中下游水文特点和渔业资源状况的研究,分析了该区域水文与饵料生物、渔业资源的关系。结果表明:汉江中下游中段的水文变化趋势适宜于产漂流性卵鱼类的繁殖;由于水文状况,汉江中下游的鱼类生长与繁殖季节晚于长江干流;4—6月的水文状况适宜下游江段饵料生物的生长;汉江中下游的饵料生物丰富,为鱼类的生长与繁殖提供了良好条件;汉江下游主要经济鱼类年龄组成简单,种群中以小型鱼类为主。     

Seasonal movement, dispersal, and home range of Northern Snakehead Channa argus (Actinopterygii, Perciformes) in the Potomac River catchment

Knowledge of the movement behaviour and dispersal ability of non-native species can aid in their management by informing risk assessments and the development of control strategies. To improve understanding of the seasonal movement and dispersal behaviour of Northern Snakehead (Channa argus), we implanted 49 fish in the Potomac River with radio tags and tracked movements from October 2006 to 2007. In addition, we tested the hypotheses that activity level, dispersal ability, and home range size varied with fish size. Home range was calculated for 24 fish. Of these, 19 exhibited stable home ranges averaging 1.2 km² in size. Thirteen fish (31% of survivors) dispersed an average distance of 18 km between 30 April and 7 June, mostly upstream (92%) and across the main river channel. Fish moved greater distances during the pre-spawn season compared to the spawning season. There was no relationship between fish length and any behavioural measure. Upstream dispersal was restricted by barriers such as dams; therefore, Northern Snakehead can likely disperse greater distances than observed here. Our observations demonstrate the invasiveness of Northern Snakehead by showing that a large portion of adults dispersed over considerable distances, suggesting spread may be rapid in large, open freshwater systems.     

Assessing the effect of Separation Levee Project on Chinese sturgeon (<Emphasis Type="Italic">Acipensor sinensis</Emphasis>) spawning habitat suitability in Yangtze River,China

Chinese sturgeon (Acipenser sinensis) is a protected anadromous fish species. The migration pattern of the fish has been blocked by the construction of Gezhouba Dam, reducing the natural spawning site length to less than 7 km along the Yangtze River. However, the fish has since established an alternative spawning ground in the narrow reach downstream of Gezhouba Dam. To enhance navigation, a Separation Levee Project (SLP) was implemented in the new-found spawning habitat of the fish. To therefore evaluate the effect of the SLP on Chinese sturgeon spawning habitat suitability, the conditions in the spawning habitat were simulated using River2D (a two-dimensional hydrodynamic model). Two main approaches (habitat kinetic energy and circulation metrics) were used in the simulation. The study showed that SLP only slightly changed the physical conditions in the spawning habitat. Using hydrodynamic simulation, the weighted usable area (WUA) before and after the SLP construction was also computed and habitat preference curve developed for water depth and velocity. On the average, SLP reduced WUA—a finding that was consistent with field-measured data. Based on WUA, the habitat conditions were more sensitive to SLP proximity than metrics based on velocity gradients. SLP posed detrimental impacts on the suitability of spawning habitats of Chinese sturgeon. The findings in this study provide further basis for the protection and restoration of Chinese sturgeon spawning habitats in especially the lower reach of Yangtze River.     

Differences in growth between maturing and non-maturing male Atlantic salmon, Salmo salar L., parr

Sibling male Atlantic salmon parr that matured tended to be the larger fish in January, but their monthly specific growth rates between January and July did not differ from those of non-maturing fish. Maturing fish had lower condition factors in March, but greater increases in condition factor during April, exceeding those of non-maturing males by May. In maturing males, feeding rates between July and September, and specific growth rates in August and September, were lower than those of immature fish. Consequently, the mean size of immatures equalled or exceeded that of maturing males by October. Maturation rates were strongly correlated with increases in mean condition factor only during April.     

Movement patterns of adult red drum, <Emphasis Type="Italic">Sciaenops ocellatus</Emphasis>, in shallow Florida lagoons as inferred through autonomous acoustic telemetry

Acoustic telemetry was employed to resolve seasonal and daily movement patterns of adult red drum (Sciaenops ocellatus) in the northern Indian River Lagoon system, Florida. From May 2006 to September 2008, 44 tagged fish were tracked within an array of 34 autonomous receivers with individuals detected for up to 654 days. Most red drum exhibited strong site fidelity from winter through early summer with movement rates increasing significantly during fall spawning months. While some fish migrated to the nearest ocean inlet at this time, the majority remained within the lagoon year-round suggesting that true estuarine reproduction, a behavior uncommon or poorly documented elsewhere is the dominant life history strategy locally. Diel movement patterns were also pronounced and indicated changing depth preferences over a 24 h period. Despite a harvest prohibition on large red drum, long-term estuarine residency coupled with high angling pressure (41% recapture rate in 50 months) suggest that post-release angling mortality and sub-lethal effects to growth and reproduction may strongly influence the strength of adult size classes.     

Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.     

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Down‐regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d . total length of the sampled fish was 32·7 ± 3·1 cm and mean ± s.d . age was 6·2 ± 1·5 years. Measurements of atresia were performed using the ‘profile method’ with the intensity of atresia adjusted according to the ‘dissector method’ (10·6% adjustment; coefficient of determination was 0·675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down‐regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.     

Comparative analyses of reproductive activity in Schizodon knerii (Steindachner, 1875) (Characiformes: Anostomidae) in three sections of the São Francisco River basin

This paper aims to establish possible changes in the main reproductive parameters of the so‐called piau‐branco, Schizodon knerii, in three sections of the São Francisco River basin. Fish (n = 388) were captured quarterly between May 2012 and April 2013 from three sections of the São Francisco River (SFR): section 1 = Três Marias Reservoir (TMR), a lentic environment; section 2 = SFR, the first 34 km downstream of TMR, a lotic environment in which the temperature, oxygen levels, and flow are not suitable for reproduction; section 3 = SFR, 34–54 km downstream from TMR after the confluence with the Abaeté River, a lotic environment in which temperature, oxygen levels and flow are suitable for reproduction. In section 2, females and males showed lower values of total length and body weight in relation to fish from sections 1 and 3. The reproductive mode of S. knerii in sections 1 and 3 exhibited a prolonged reproductive period, parceled spawning, and a reproductive peak from January to March. In section 2, neither spawning females or spermiated males were captured, probably due to the fact that this section receives cold water with low oxygen levels from the hypolimium of the dam that presents thermal stratification in the summer. This study showed in section 2, immediately downstream of the Três Marias Reservoir, that S. knerii does not reproduce successfully.     

Observations on the age, growth, reproduction and food of the pike Esox lucius (L.) in two rivers in southern England

Opercular bones of 261 pike from the River Stour and 117 from the River Frome were used for age and back-calculated growth determinations. The annuli were laid down during late April and early May and most growth occurred between May and September. Pike growth in the two rivers was comparable with the fastest growth in other waters, though Frome pike grew slightly faster than Stour pike. Spawning occurred from the end of March into May. Elaboration of the ovaries commenced in September and was virtually completed by February, whereas the testes reached their maximum weight in October and maintained it until spawning. Immature pike had an annual cycle of condition reaching a maximum in May and a minimum during the winter. The gonad cycle affected the condition of mature females which had their minimum condition in mid-summer. The fecundity of Stour pike is expressed by the formula: log₁₀ egg number =3.56 log₁₀ fish length (mm) – 5.40. Approximately 75% of all Stour pike were sexually mature by age II and these fish were, on average, larger than immature pike of the same age. The most numerous items in the diet of pike were small cyprinids, 30–80 mm fork length, although pike over 700 mm long ate larger fish. Few salmonids appeared in the diet of either Frome or Stour pike. The percentage of empty stomachs was highest in Stour samples taken during the summer, shorter digestion times and longer feeding periods in this period are suggested as reasons for the apparent anomaly.     

Restoration of naturally reproducing and resident riverine lake sturgeon populations through capture and transfer

The Winnebago System, Wisconsin, is home to one of the largest Lake Sturgeon Acipenser fulvescens populations in North America. Although there are >50 known spawning sites utilized by Lake Sturgeon in the 200 km of the lower Wolf River upstream of Lake Winnebago, the construction of two dams >90 years ago eliminated the ability of Lake Sturgeon to access 18.5 km of river up to their ancestral spawning grounds below Keshena Falls. Given the cultural importance of sturgeon to the Menominee Indian Tribe of Wisconsin, expanded efforts aimed at restoring Lake Sturgeon spawning and a resident population to the upper Wolf River commenced in 2011. To meet these objectives, 100 or more Lake Sturgeon per year were captured below the dams, and transferred upstream to the Wolf River within the Menominee Reservation. All transferred fish were PIT tagged and 245 fish were surgically implanted with 10 year acoustic transmitters to determine spawning locations and monitor post‐release movement. The first five transfer cohorts contained 621 Lake Sturgeon, with spawning activity observed below Keshena Falls each spring following release. Gravid fish transferred within 3 weeks of spawning exhibited higher spawning rates above the upstream dam (70.2% females; 73.9% males) than gravid fish transferred in late fall (41.8% females; 41.2% males). Spawning documented below Keshena Falls and within the Red River represent the first spawning activity at these locations in >100 years. Lake Sturgeon transferred in early fall displayed higher retention rates, 2‐5 years post‐tagging, in the pool upstream of both dams (10.4%) compared to the late fall (3.1%) and spring transfers (7.4%). Natural reproduction was documented through capture of larval Lake Sturgeon immediately below Keshena Falls in 2013. These results demonstrate that capture and transfer can be utilized as a cost‐effective and biologically‐effective tool for Lake Sturgeon spawning stock and population restoration.     

Different growth trends of whitefish (Coregonus lavaretus) forms in the northern Baltic Sea

The sea growth of two whitefish forms, anadromous (Coregonus lavaretus lavaretus) and sea‐spawning (Coregonus lavaretus widegreni), was analysed using samples collected from the commercial sea catch in the Gulf of Bothnia (GoB) in the northern Baltic Sea during 1998–2014. In the GoB area, these two forms are possible to identify because the gill‐raker number and size at maturity vary between forms. The growth rate of the forms is linked to their feeding area. Sea‐spawning whitefish, which has a feeding migration near its home site, was shorter in the northern GoB (66°N–64°N) at the ages of 3–11 than those in the southern GoB (64°N–60°30′N). In the data, most whitefish were caught with gill nets in the GoB. The mesh sizes of gill nets capturing the anadromous form were mostly 35–45 mm, while those capturing the sea‐spawning form were <35 mm in the northern GoB. It is likely that the different growth trends for small and large whitefish were connected with differences in their recruitment for fishing. The length of anadromous females at the age of four sea years increased significantly, but the length of six‐year‐old anadromous female whitefish decreased over the catch years from 1998–2014. In contrast, the length of slow‐growing sea‐spawning whitefish of six years or older increased significantly in relation to the catch year in the gill‐net catch. The increase in the growth of young age groups in both forms was probably associated with the increasing temperature and the low fishing pressure on small fish. The decreasing age at capture for both forms and the depression of the mean size of old anadromous whitefish are signs of high fishing pressure with a high gill‐net effort that selectively removes the largest and oldest individuals of both forms.     

The biology of stone loach Barbatula barbatulus in the Rivers Goloustnaya and Olkha, East Siberia

Five hundred and four stone loach 63–202 mm in total length, of I + to 8 + age groups, were sampled in two rivers of East Siberia from April to October 1989–90. This paper presents data on the seasonal dynamics of fecundity, ripening, fatness and feeding intensity. A second spawning from the end of August to October has been identified for the first time for this species. The absolute fecundity ranged from 1710 to 27600, and the relative fecundity varied from 216 to 833 eggs g⁻¹: (fish weight). Stone loach in the River Olkha grew faster than those in the River Goloustnaya and, according to this index, are closer to stone loach from streams of northern England.     

Food selection and growth of young snakehead Channa striatus

Food selection and growth of young snakehead Channa striatus were studied in the laboratory and in a field trial. In the laboratory, first-feeding snakehead larvae of 6–7 mm total length (TL) with a mouth opening of 0.55 mm selected for Artemia nauplii, and against formulated feed. Fish began feeding on formulated feed at 12mm TL when their mouth width reached 1.0mm. In both laboratory and field trials, snakehead diets changed as fish size increased. For fish 15–20 mm TL, cladocerans and copepods were 96.5% of their diet. With fish 30–40 mm TL, zooplankton consumption was greatly reduced while benthic organism consumption increased. Fish 45–50 mm TL fed exclusively on benthic invertebrates. Diet shift from zoo-plankton to benthic invertebrates was not due to reduced zoo-plankton availability, but was instead related to changes in gill raker structure. Low density of benthic invertebrates in the field trial caused reduced fish growth rates when fish switched diets from zooplankton to benthos. Our results indicate that snake-head can take Artemia nauplii as a larval starter food, then accept formulated feed at ≥12 mm TL. Zooplankton can serve as food for snakehead < 40 mm, but formulated feed should be provided for larger fish which are unable to catch zoo-plankton.     

Length–weight relationships and reproductive parameters of Amblyceps apangi Nath and Dey, 1989 from Nagaland,India

The present study describes certain biological parameters of a hill stream catfish, Amblyceps apangi Nath and Dey, 1989 first described from Arunachal Pradesh, India. The distributional range of the fish was later recorded from the states of Manipur and Nagaland. The fish is very rare and this is the first report on certain biological parameters based on collections (140 males, 105 females) from streams in the Doyang watershed, a tributary of the Brahmaputra River. The value of the allometric coefficient (b) indicated close to isometric growth in males (2.989) and negative allometric growth in females (2.945). The relative condition factor was found to be close to 1 in different size groups. Both males and females attained first maturity (M₅₀) in length group 6.0–7.0 cm. Peak values (Male 0.424, Female 1.465) in the gonadosomatic index (GSI) occurred from April to May, indicating one spawning season per year. The overall female to male ratio was 1 : 1.33. Absolute fecundity ranged from 17 to 122 for fishes of total length 6.34–10.3 cm.     

Habitat use and population characteristics of potentially spawning shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820), blue sucker (Cycleptus elongatus (Lesueur, 1817), and associated species in the lower Wisconsin River, USA

The goal of this study was to compare the possible locations, timing, and characteristics of potentially spawning shovelnose sturgeon (Scaphirhynchus platorynchus), blue sucker (Cycleptus elongatus), and associated species during the spring of 2007–2015 in the 149‐km‐long lower Wisconsin River, Wisconsin, USA, a large, shallow, sand‐dominated Mississippi River tributary. A 5‐km index station of two pairs of rocky shoals surrounded by sandy areas was electrofished for shovelnose sturgeon and blue sucker in a standardized fashion a total of 40 times from late March through mid‐June, the presumed spawning period. On one date in 2008 and two dates in 2012, all rocky shoals and adjacent sandy areas in the lowermost 149 km of the river were also electrofished for both species. Shovelnose sturgeon and blue sucker appeared to spawn in the limited rocky areas of the river along with at least four other species: mooneye (Hiodon tergisus), quillback (Carpiodes cyprinus), smallmouth buffalo (Ictiobus bubalus), and shorthead redhorse (Moxostoma macrolepidotum), usually at depths of 0.8–2.0 m and surface velocities of 0.4–1.0 m/s. However, apparently spawning shovelnose sturgeon were found only on mid‐channel cobble and coarse gravel shoals within a single 7‐km segment that included the 5‐km index station, whereas apparently spawning blue suckers were encountered on these same shoals but also more widely throughout the river on eroding bluff shorelines of bedrock and boulder and on artificial boulder wing dams and shoreline rip‐rap. Both species showed evidence of homing to the same mid‐channel shoal complexes across years. Blue sucker tended to concentrate on the shoals earlier in the spring than shovelnose sturgeon, usually from late April through mid‐May at water temperatures of 8.0–15.5°C along with quillback and shorthead redhorse. In comparison, shovelnose sturgeon usually concentrated on the shoals from mid‐May through early June at 13.5–21.8°C along with mooneye and smallmouth buffalo. Based on recaptures of tagged fish, at least some shovelnose sturgeon and blue sucker returned to the shoals at one‐year intervals, although there was evidence that female blue sucker may have been more likely to return at two‐year intervals. Most shovelnose sturgeon could not be reliably sexed based on external characteristics. Spawning shovelnose sturgeon ranged from 487 to 788 mm fork length, 500–2400 g weight, and 5–20 years of age, whereas spawning blue sucker ranged from 495 to 822 mm total length, 900–5100 g weight, and 5–34 years of age, although age estimates were uncertain. Females were significantly larger than males for both species although there was overlap. Growth in length was negligible for tagged and recaptured presumably spawning shovelnose sturgeon and low (3.5 mm/y) for blue sucker, suggesting that nearly all growth may have occurred prior to maturity and that fish may have matured at a wide range of sizes.     

Reproductive biology and growth of bluestripe herring Herklotsichthys quadrimaculatus (Rüppell, 1837) in the northernmost waters

In order to examine the reproductive biology and growth of Herklotsichthys quadrimaculatus in the northernmost part of its reproductive range, the size frequency, gonadal development, and otolith daily increments of this species were collected from the coastal waters of Okinawa Island, southern Japan. Juveniles (<25 mm standard length, SL) were found from April to August. Their size increased to ca. 100 mm SL in November and subsequently remained unchanged. The gonadosomatic index of females was higher (>3.0) between March and August, which was the estimated spawning period. The modal hatching period back‐calculated from otolith daily increments was from April to May, which would be the peak of spawning. Because mature and spent ovaries also contained mature and immature oocytes, it was concluded that females spawn several times during the spawning season. Age determination from otolith increments showed logistic growth up to 97 mm (ca. 180 days post‐hatch), after which growth was almost stagnant. Maximum size and age were 121.6 mm SL and 384 days, respectively. The adult size decreased between August and September, indicating a change in the age cohort. Thus, the fish reached the end of their lifespans after spawning. Some of these ecological features were different from those of a previous study performed in southern areas; these differences suggest a flexible life history that could change to adapt to the surrounding environment.     

Hydrological Variation and Fish Assemblage Structure in the Middle Wabash River

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (?54%) relative to available pool area (?2%). Fine sediment levels (<0.063 mm) significantly increased within spawning substrate (p=0.01). Water temperature and dissolved oxygen were adequate (mean 15.8?°C, >6.0 mg l^?1, respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Young-of-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.     

Behavioural Interactions and Hormones in Naturally and Hatchery‐Spawned Chinook Salmon

Artificial breeding programmes commonly lead to domestication, which is associated with many behavioural differences that can reduce the success of animals released into natural environments. To better understand the factors contributing to domestication, we used a captive population of Chinook salmon (Oncorhynchus tshawytscha) to partition hormonal and behavioural differences to effects of the breeding method and rearing environment. We compared 9‐mo‐old juveniles from three lines that shared a common genetic background: (1) the Channel line produced by natural spawning and reared in a low‐density environment with a natural substrate for approx. 6 mo before being transferred to the hatchery; (2) the Hatchery line produced by artificial spawning; and (3) the Transfer line produced by natural spawning but reared in the hatchery from the eyed‐egg stage. Plasma concentrations of 11‐ketotestosterone (11‐KT) and cortisol were measured in groups of 150 fish and again after 4 d of social interactions in groups of six fish. There was no difference in 11‐KT among lines in large groups, but in small groups, Transfer fish had lower 11‐KT concentrations and were significantly less aggressive than both Channel and Hatchery fish. Regardless of group size, concentrations of the stress hormone cortisol were nearly twofold higher in Channel fish than in Hatchery and Transfer fish. Furthermore, the elevated cortisol concentrations in Channel fish were associated with 35% lower feeding rates than in the other two lines. Our study details complex behavioural and hormonal responses to breeding method and rearing environment in juvenile salmon.     

Reproductive seasonality of the detritivorous fish <Emphasis Type="Italic">Cyphocharax abramoides</Emphasis> (Kner, 1958) (Characiformes: Curimatidae) in flooded rivers of the eastern Amazon

The Lower Anapu River, Eastern Amazon, has a discrete flood pulse with narrow flooded areas due to the reduced influence of tides. In this environment, local precipitation might act as an important factor in the input of detritus, which can serve as a trigger for fish reproductive period. Therefore, this paper aims to determine the effects of local precipitation on the reproductive ecology of an abundant detritivorous fish in flooded rivers. Between May 2012 and April 2013, 886 specimens (471 females and 415 males) were captured monthly using gill nets. Individuals were measured, weighted, sexed, and the gonadal development stage was defined macroscopically and confirmed histologically. Sex ratio, length-weight relationship (LWR), condition factor (k), Gonadosomatic Index (GSI), relative frequency of maturity stages, and size at first gonadal maturity (L₅₀) were estimated and tested in relation to rainfall periods. There was no difference between the expected sex ratio (1:1), and both males and females showed polyphasic growth. The condition factor indicated higher values at the beginning of the rainy season and lower values during the dry season for both sexes. GSI and relative frequency of mature individuals indicated a long reproduction period with gonadal investment starting within the dry season until early in the rainy season for spawning within the rains. The L₅₀ value showed that males reach sexual maturity before females. Results indicated a reproductive pattern strongly influenced by rainfall, corroborating the importance of local precipitation for lacustrine environments.