Distribution, reproduction and growth of the catfish, Chrysichthys walkeri (Gunther) in the Lekki Lagoon, Nigeria

An investigation was made on the biology of the catfish, Chrysichthys walkeri (Gunther) occurring in the Lekki Lagoon. The catfish was evenly distributed over the six sampled stations of the lagoon with the sites of the shallow water stations probably serving both as breeding and nursery grounds.
Fecundity estimates for this species ranged from 896 to 4168 eggs. The average number of eggs per female was 2084. Laboratory incubated eggs hatched after 3 days with the yolk sac being completely absorbed on the seventh day. The fry averaged 8.6 mm on their first day of life.
The catfish attained a maximum total length of 25.7 cm within a period of 2 years. There were no significant differences in the growth pattern of this species during the dry and rainy seasons.     

Reproduction characteristics of a stunted population of rudd, <Emphasis Type="Italic">Scardinius erythrophthalmus</Emphasis> (Linnaeus, 1758) living in the Anzali Lagoon (the southwest Caspian Sea,Iran)

A total of 486 specimens of Scardinius erythrophthalmus caught in the Anzali lagoon, a large lagoon located in the southwest Caspian Sea (Iran), between March and June 2007 were examined. Age determination showed that the maximum ages observed were 4+ in males and 5+ in females. Isometric growth was identified from length-weight relationship in males, females and pooled data. There was no significant difference from parity in the overall sex ratio of 252 males to 234 females. The fish spawn from mid April to late May, with peak spawning in mid May with the highest average GSI value of 7.12 and 13.52 for males and females respectively. The absolute fecundity ranged between 1482–59620 eggs with the mean of 9287.87 eggs while relative fecundity ranged from 127.8 to 1737.6 eggs/g with the average of 709 eggs/g of body weight. Egg diameter ranged from 0.43 to 1.23 mm with a mean of 0.73 mm. The characteristics of rudd in the stunted population from the Anzali lagoon differ markedly from those of other localities of its range.     

Population dynamics of perch, Perca fluviatilis L. in Slapton Ley, Devon

Perch, Percafluviatilis L. were studied in Slapton Ley which is a eutrophic freshwater lagoon in south Devon, England. The perch were caught in traps from February 1970 to June 1971. The traps selected males during the spawning season. The water temperature did not affect the numbers of trapped fish directly, but the sight of perch in the traps appeared to attract others. Sex ratios were found to be equal in the first 2 years of life but older year classes were predominantly female. The population consisted of young individuals. Males were found to mature in their first year and most females matured in their second. The fecundity varied from an average of 1000 eggs in perch n i the 9.75 cm length group to 30,500 eggs in fish in the 27.75 cm group. A few shoals of perch moved throughout the Ley although the majority of fish stayed in the same area. Population estimates showed a range from 10,000 to 95,000 for fish 9.75 cm and above. The large variations in population estimates and survival rates were attributed to the necessity of using traps which had variable catches and to the harmful effects of handling the perch. Chironomids were important in the diet of perch of all sizes. Plankton and Asellus were other important foods, the latter especially during the winter months. Perch 11.5 cm to 13.9 cm selected the widest range of food organisms. Only perch 14.0 cm and above ate fish.     

The reproductive biology of an endemic cyprinid,Zacco pachycephalus,in Taiwan

Synopsis Reproductive parameters including body weight-length relationship, condition factor, gonadosomatic index (GSI) and fecundity of an endemic cyprinid,Zacco pachycephalus, were studied from October 1991 to January 1993. Although the condition factor was similar between both sexes, GSI values of female (3.72 to 14.24%) were significantly larger than that of males (0.21 to 2.23%) during the major breeding season. The number of yolky eggs per fish ranged from 459 to 2059. Ovum size distribution, annual GSI value, and recruitment of juvenile fish indicated thatZ. pachycephalus conducted two major spawning activities in spring (February to April) and summer (June to August). The larger GSI value and number of yolky eggs in spring compared to those in summer implies thatZ. pachycephalus has evolved a reproductive style by investing more energy in spring to avoid the damage of summer freshet on its recruitment success. The mating behavior ofZ. pachycephalus is similar to that of otherZacco fishes.     

Condition factor and diet of Chrysichthys nigrodigitatus and Chrysichthys auratus (Siluriformes: Bagridae) from Aiba Reservoir, Iwo, Nigeria

Chrysichthys nigrodigitatus and C. auratus are important, highly valued and threatened freshwater species. To contribute with their ecological knowledge, the condition factor and diet of these two congeneric species were studied between April 2005 and April 2006. Food items of fish were evaluated by occurrence and numerical abundance methods, and the possible changes among sexes, seasons and sizes were considered. Results showed that generally C. nigrodigitatus were better conditioned than C. auratus. The males of C. nigrodigitatus and females of C. auratus were in better condition than their respective opposite sex throughout the year, and during the wet season compared to the dry. The food items of C. nigrodigitatus and C. auratus were similar and comprised twelve species belonging to five groups: Insecta (three species), Crustacea (five species), Arachnida (one species), Rotifera (one species) and Mollusca (two species). Other food items included fish scales, unidentified green eggs, plant parts, detritus and sand. Insecta and Crustacea dominated the food items in both species. For C. nigrodigitatus, insect consumption increased with fish size, while Crustacea items decreased (from 89.59% for 8.1cm - 12.0cm size class to 1.58% for 20.1cm - 26.0cm size class). However, while C. auratus smaller sized fish preferred Crustacea (98.72% for 8.1cm -12.0 cm size class), larger sized fish had both groups in relatively similar amounts. Schoener Overlap Index for both species and between seasons is 1.00. Diet breadth ranged from 0.00-1.47 for C. nigrodigitatus and 0.00-1.32 for C. auratus. Food Richness ranged from 0.00-1.44 for both species. Gut Repletion Index for C. nigrodigitatus and C. auratus are 76.39% and 76.27% respectively. Although, there is considerable similarity and overlap in the utilization of food resource for both coexisting species, condition factor and feeding behavior suggest strategies to reduce intra- and interspecific competition.     

Aspects of the biology of grey mullet, Mugil cephalus L., adult populations of a coastal lagoon in Sri Lanka

The biology of grey mullet, Mugil cephalus L., adult populations in a coastal lagoon in Sri Lanka is presented. The percentage of grey mullet catches increased with increasing salinity. The larger fish were found in the deeper areas and the relationship of total length to depth was L = 8.4602e^{0.0058 D} where L = total length and D = depth (cm). The overall female to male ratio was 0.95 : 1.0 and seasonal variation in the sex ratio is considered to be caused by the differential timing in the spawning migrations of the two sexes. Males mature at 34.0 cm and females at 31.5 cm. The main spawning season was between January and May and it is hypothesized that the breeding season is geared to utilize the favourable time period, for growth of fry, in the lagoon. Grey mullet sheds its eggs in batches. Fecundity varied from 0.45 to 4.2 million in fish ranging in length from 32 to 56 cm and in weight from 0.7 to 2.2 kg. Fecundity was significantly correlated to body length and weight and gonad weight.     

Control of Gonadal Maturation and Regression by Experimental Variation of Environmental Factors in the Mormyrid Fish, Mormyrus rume proboscirostris

We used spawning, external appearance of the females and in part histology of gonads of the African mormyrid fish Mormyrus rume proboscirostris to evaluate the reaction of the fish to experimental variation of environmental factors. Conductivity changes are sufficient to induce gonadal maturation (decrease of conductivity) and regression (increase of conductivity), respectively. Increase of water level and simulation of rain at constant conductivity values did not induce gonadal maturation and spawning. Neither males nor females of M. rume proboscirostris showed postbreeding refractoriness. Social stress apparently prevented complete gonadal maturation and successful spawning. The females laid on average 364 eggs per fractional spawning; the spawning intervals were 21 days. Hatching rate amounted to about 40% in all experiments taken together.     

Reproductive biology of Bagrus docmak in the Victoria Nile,Uganda

Aspects of the reproductive biology of Bagrus docmak in the Victoria Nile were investigated between November 2005 and October 2006. Macroscopic and histological analysis of the gonads confirmed it as an asynchronous batch spawner which spawns throughout the year with bimodal spawning peaks coinciding with rainfall seasons. The first spawning peak occurred from March to May, the second from September to November. The sex ratio did not significantly deviate from 1:1. Length at sexual maturity was 33.6 cm and 31.6 cm fork length (FL) for females and males, respectively. Batch fecundity ranged from 1 000 eggs in 34 cm FL fish to 43 000 eggs in 79 cm FL fish, and correlated linearly with FL (r = 0.72) and body weight (r = 0.79). Mean relative batch fecundity was 6 eggs g^?1 (SE 2). These results could guide research into the possibility of artificially inducing the fish to spawn, and its subsequent culture.     

Some aspects of the biology of Petenia krausii Steindachner (Pisces: Cichlidae) in Lake Valencia, Venezuela

Petenia kraussii Steindachner (Pisces: Cichlidae) was collected from Lake Valencia, Venezuela from April 1973 to April 1974. A total of 457 specimens were examined for stomach contents, and 471 were analyzed for length-weight relationship, sexual condition including fecundity and parasitism. P. kraussii is primarily a plankton feeder when small and utilizes benthic invertebrates after attaining about 10 cm standard length. The larvae of a benthic ephemeropteran, Campsurus sp. (Hexigenidae) was the most important single food item with gastropods and fish eggs also being found consistently in stomachs. No mature male fish were found, and only 17 of 471 fish could be identified as males, while 157 were females. Gravid females contained an estimated mean of 6266 eggs and matured at about 18 cm standard length and 100 g live weight. It was not possible to determine age from either scale or otoliths.     

Reproductive biology of anadromous arctic char,Salvelinus alpinus (L.)? in the Cumberland Sound area of Baffin Island

The ovaries of anadromous arctic char, Salvelinus alpinus (L.), captured during 1973 from four high arctic rivers on Baffin Island started to increase in weight early in July and were at their heaviest in mid-September just before spawning. At this time, 40 cm (615 g) char from two rivers contained ovaries weighing 17.0 g (dry) which differed significantly from the 22.5 g gonads of comparable char from the other two areas. Gonadal development in male fish began in June and the diameter of testes at full maturity (3.0–4.0 cm) was similar regardless of river system. Fecundity of comparable fish varied significantly among the rivers with char 40 cm in length containing 1400–2400 eggs while the corresponding values for 60 cm (i.e. 2050 g) char ranged from 4000–5500. The diameter of both immature and mature eggs was similar regardless of system. Values for immature eggs averaged 0.64 mm in 40 cm fish and 1.60 mm in 60 cm specimens. Diameter of mature eggs, on the other hand, was considerably greater (3.2 and 4.3 mm, respectively). Maturity was first reached at age 10 (i.e. 35 cm) in both males and females and maturing fish of both sexes were not always restricted to fresh water. Redd construction occurred at a depth of one to at least 11 m at a temperature of 0.5–4.0° C. The percentage of eggs retained in the body cavity after spawning varied from 0.22–1.50 and the mortality rate of spawned eggs was extremely low.     

On the biology of an estuarine population of the clupeidPellonula afzeliusi (Johnels) in Lagos Lagoon,Nigeria

The length-weight relationship, condition factor, fecundity and food and feeding habits ofPellonula afzeliusi (Johnels) in Lagos Lagoon were investigated. The standard length of 1832 specimens examined ranged between 3.5 and 9.4 cm (total length 3.9 cm–11.4 cm) and was larger than reported elsewhere in West African man-made lakes. Specimens exhibited positive allometric growth. Their condition factor increased with individual size. Females had a slightly higher condition factor than males. The number of mature ova per female ranged between 330 and 33,649. There was a higher correlation between fecundity and weight than between fecundity and length. The major food items were crustaceans, insects and fishes. There were distinct differences in the feeding habits in relation to size. Variations were observed in the monthly analysis of food items.     

The food and feeding habits of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters

The food habits of the silver pomfret, Pampus argenteus (Euphrasen 1788), in Kuwait waters were investigated by examining the stomach contents of 738 specimens collected from May 1996 to April 1997. Their diet consisted of a broad spectrum of food types, but Crustacea were dominant, with copepods and their eggs constituting 39 % other non-copepod Crustacea constituted 16 %. The next major food group was Bacillariophyta (21 %), followed by Mollusca (11 %), fish scales (10 %) and, finally, fish eggs and larvae (3 %). In summer the species fed on a wider variety of food items than in winter. Copepods, other non-copepod crustaceans, and molluscs tended to occur in the stomachs in higher frequencies with an increase in P. argenteus size (up to 18.5–20.4 cm), while the bacillariophytes tended to increase in stomachs at fish sizes between 22.5–24.5 cm. Analysis of monthly variations in stomach fullness indicated that feeding intensity fluctuated throughout the year, with a low during August and September, corresponding to the spawning period.     

On the biology of bream, Abramis brama (L.) in Lake Peipsi in 1994

The population of bream in L. Peipsi was studied with respect to age, growth rate, condition factor (according to Fulton) and length-weight relationship in 1994. That autumn the bream population in L. Peipsi consisted of fishes aged from 0+ to 15+. During the first year bream reached an average body length of 7.9 cm (the commercial legal size (30 cm) was usually attained by the end of the 5th–6th year. The condition of bream in this lake was above the average of Estonian lakes. The relatively good growth rate and condition of bream in the lake indicates that the waterbody is appropriate for this fish.     

Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24·0–25·9 and 28·0–29·9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures ≥16·6° C and day length ≥10·7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0·7% for all ripe males and 4·1–4·2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7·8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g⁻¹ of body mass. Batch fecundity of wild females was estimated at 7·8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.     

Biological Studies of the Pearl Spot Etroplus suratensis (Pisces,Cichlidae) from three Different Habitats in Sri Lanka

The morphometry, feeding habits and reproductive biology of Etroplus suratensis, an indigenous cichlid food fish, were studied for a period of one year on specimens from three different habitats in Sri Lanka. The morphometric studies implied that the length weight relationships are curvilinear. Macrophytic fragments formed the most important component of food, although detritus, diatoms, and animal matter are also ingested. First sexual maturity is attained in the length ranges 8.0-9.0 cm in females from brackish water habitats. Fecundity ranged from 700-3900 eggs in mature specimens. The wide range of the gonadosomatic index suggests that spawning occurs several times during the year.     

金沙江中下游圆口铜鱼的繁殖生物学

根据2013—2014在皎平渡圆口铜鱼产卵场的定点亲鱼收集(n=206)和2006—2014年在金沙江中下游金安桥至巧家干流江段的流动亲鱼采集(n=70), 对圆口铜鱼的繁殖生物学进行了初步研究。定点亲鱼收集的结果显示: 圆口铜鱼雌性最小性成熟个体全长330 mm, 体质量441.0 g, 年龄4龄; 雄性最小性成熟个体全长352 mm, 体质量396.6 g, 年龄3龄; 50%个体达到性成熟的年龄和全长分别为雌性4.32龄 406 mm, 雄性4.44龄 412 mm; 繁殖群体雌雄性比为1.37﹕1, 繁殖群体中雌性年龄为4—7龄, 雄性年龄为3—7龄; 雌雄个体的性成熟系数平均值均以6龄个体最高, 分别为10.55%和3.45%; 平均卵径为0.16 cm, 卵径分布呈双峰型。定点和流动亲鱼收集的雌性性成熟个体的结果表明: 圆口铜鱼绝对繁殖力变动范围为4055—137900粒/尾, 平均值为22817粒/尾; 相对繁殖力变动范围为5—73粒/g, 平均值为20粒/g, 75.68%个体的绝对繁殖力在10000—30000粒/尾之间, 70.27%个体的相对繁殖力在15—20粒/g之间; 绝对繁殖力和相对繁殖力均随着体长和体质量的增加而增加, 其中全长、体质量与绝对繁殖力呈指数分布函数正相关, 而与相对繁殖力呈二次项函数正相关。研究结果可为长江流域圆口铜鱼资源的保护提供重要的基础数据支撑。     

Length–length relationship, length–weight relationship, gonadosomatic index, condition factor, size at maturity and fecundity of Parastromateus niger (Carangidae) in Kuwaiti waters

Analyses of morphometric parameters of the black pomfret, Parastromateus niger, in the Kuwaiti waters of the Arabian Gulf during a 44‐month study revealed the following length‐length relationships: TL (cm) = 0.63 + 1.15SL (females), TL (cm) = 0.94 + 1.14SL (males) and TL (cm) = 0.75 + 1.15SL (both sexes including juveniles). The 95% CI of the exponent in length‐weight relationship varied from 2.788 to 2.796 in females, 2.726 to 2.732 in males, 2.779 to 2.784 for both sexes and 2.590 to 2.613 in juveniles, all indicating an allometric relationship. Simultaneous analysis of Fulton’s condition factor (K) and GSI indicate that spawning in black pomfret peaks in May and June even though the fish remain in good condition throughout the spawning season. The Fulton’s condition factor was statistically discriminatory in determining the well‐being of P. niger. Variation in average maximum condition was significant between sexes and also higher in 2004 as compared to 2005. The mean size at first sexual maturity (SL_50%) was 17.5 cm for males and 29 cm for females. Fecundity ranged from 71 305 to 3 895 449 eggs and correlated positively with: (a) ovary‐free body weight (P < 0.05), standard length (P < 0.05) and ovary weight (P < 0.05), and negatively with egg size (P > 0.05). Fecundity‐total length relationship was best described by the logarithmic equation of the form F = 0.898 + 3.15 × TL^3.15. The use of results of such morphometric studies in the management of the P. niger species in the Arabian Gulf is suggested due to its growing commercial importance.     

Replenishment of fish populations in the enclosed lagoon of Taiaro Atoll: (Tuamotu Archipelago, French Polynesia) evidence from eggs and larvae

 Taiaro Atoll Lagoon is normally isolated from the ocean, but at least 125 marine fish species of 31 families are present there. We sampled fish larvae in Taiaro Lagoon and the nearby ocean in February 1994 with plankton net, neuston net and light trap to investigate which taxa were completing their life cycles in the lagoon. Concentrations of fish eggs and larvae were very high in the lagoon indicating intense spawning, but larvae of only 18 taxa of 10 families were present. Only six, a callionymid, gobiids, a hemiramphid, a microdesmid, and two pomacentrids, were present across a full range of pelagic sizes, and were clearly completing their pelagic stage in the lagoon. Four other taxa, an apogonid, two labrids and a scarid, were common, but the largest individuals were small (<5 mm) postflexion larvae. These may have been completing their pelagic stage in the lagoon. The remaining lagoonal larvae (eight taxa) were rare and at the preflexion stage, so we could only conclude that they hatched from eggs spawned in the lagoon. Nineteen taxa of 15 families found as adults in the lagoon were present outside the lagoon as larvae, but not inside, suggesting that they may not normally complete their life cycles in the lagoon. Horizontal distributions of larvae in the lagoon are apparently due to the interaction of larval vertical distribution behaviour with a wind-driven countercurrent system. Accepted: 16 October 1996     

Feeding behaviour of cod (Gadus morhua) in relation to spawning

The food consumption and egg production of 26 adult (13 female and 13 male) Atlantic cod ( Gadus morhua ) were monitored during prespawning, spawning and postspawning periods. Females spawned from late January to mid-April. Feeding activity occurred from December to early January and ceased for females, on average, 36 days (15–54 days) before the onset of spawning. The duration of spawning by females was, on average, 42 days (10–61 days) and feeding was suppressed by both sexes during the first three-quarters of each female's spawning period. Mature females went, on average, 70 days or 19% of the year without eating. An abrupt increase in feeding activity, particularly by females, occurred during the last quarter of spawning or shortly after the release of the last egg batch (on average, feeding started again after 91% of a female's eggs had been released or 82% of egg batches). Females consumed greater quantities of food than males during both winter and postspawning feeding periods. During spawning, females lost, on average, 29% of their body weight and males 14%. Fecundity ranged from 0.75 to 3.97 million eggs per female. The volume of eggs produced by four individual females (range = 1285–5995 ml in four to 11 batches) ranged from 99 to 195% (mean 150%) of a female's postspawning body volume. Six immature cod fed throughout the experimental period and gained, on average, 8% of initial body weight. Laboratory results were supported by stomach fullness index values of Georges Bank cod exhibiting different maturity states.     

Is fecundity in plaice (Pleuronectes platessa L.) down‐regulated in response to reduced food intake during autumn?

The effect of controlling food intake during the autumn, which is the time of late vitellogenesis, on fecundity, atresia and follicle and ovary growth was examined for plaice Pleuronectes platessa . Eighteen fish were kept in individual pens and either fed on a high or low ration diet. Fish which increased in whole body condition exhibited an increase in carcass condition which means that when food intake is sufficient to maintain whole body condition some resources are used as storage. Follicle growth rate was positively correlated with change in Fulton's condition and total atresia was negatively correlated with change in Fulton's condition. Thus, the rate of vitellogenesis was dependent on the availability of an exogenous food source. Fecundity at the end of the experiment was positively correlated with mass and total length. Food intake had no effect on relative fecundity; however, fish which had a lower food intake lost mass and had a greater intensity of atresia, lowering their absolute fecundity. One fish in a very low condition at the start of the experiment skipped spawning and one fish exhibited a decrease in average follicle diameter during the experiment which is hypothesized to be a prelude to mass atresia.