Variation In Gonadosomatic Index Research Articles

Reproductive period and fecundity of Serrapinnus piaba (Characidae: Cheirodontinae) from the rio Ceará Mirim, Rio Grande do Norte, Brazil

Specimens of Serrapinnus piaba were collected monthly from April 2001 to April 2002 in the rio Ceará Mirim, Rio Grande do Norte State, Brazil. The reproductive period, determined through the monthly variation of the gonadosomatic index (GSI) and maturation stages, occurred from January to April. Non-parametric Spearman test was performed in order to test correlation of monthly GSI variation in males and females with water temperature, rainfall and day length. Rainfall and Temperature were correlated with GSI variation in females only and day length showed a negative correlation with GSI variation of males only. It was verified the presence of hooks on the anal fin of mature and maturing males along all the period of study. The absolute fecundity mean was 441 (±178.08) oocytes, determined by the number of yolky oocytes counted in 27 mature female gonads. The relative fecundity, estimated by the number of yolky oocytes divided by milligram of total body weight was 0.74 (± 0.19).

Breeding, growth, mortality and yield of the mudskipper Periophthalmus barbarus (Linneaus 1766) (Teleostei: Gobiidae) in the Imo River estuary, Nigeria

We studied the reproductive biology, growth, mortality, recruitment pattern and yield-per-recruit to the fishery of the mudskipper Periophthalmus barbarus (= P. papilio) in the intertidal swamps of the Imo River estuary in the south-eastern Nigeria. Monthly variation in gonadosomatic index reveals that the males spawn once in a year from February to May and the females from March to May. The size at which 50% of the specimens matured was 10.2 cm (total length) for females and 10.5 cm for males while the median size at spawning was 10.8 cm for females and 11.9 cm for males. We collected and analysed 12 consecutive months length–frequency data using FISAT software. Fitting the seasonalized von Bertalanffy growth function to these data gave the following results: L ∞=21.6 cm total length, K=0.55 yr −1 , C=0.9, WP=0.2 of the year. Using the seasonalized catch curve procedure, the estimated instantaneous total mortality coefficient Z=4.21 yr −1 . The instantaneous fishing mortality coefficient F=2.86 yr −1 , and the instantaneous natural mortality coefficient M=1.35 yr −1 . Our computed exploitation rate E=0.68 showed that fishing pressure on the stock is high. This was supported by the results of our relative yield-per-recruit analysis which showed the predicted maximum exploitation level E max=0.51 which was lower than the current exploitation rate ( E=0.68).

Effect of Season and Age on the Gonadosomatic Index of Milne-Edwards' Sifakas (Propithecus diadema edwardsi) in Ranomafana National Park, Madagascar

Aiming to explain individual variation in gonadosomatic index (testicular volume per body weight), we examined the relationship between gonadosomatic index (GI), age, and season in a wild, seasonally breeding lemur—the Milne-Edwards' sifaka (Propithecus diadema edwardsi). Between 1987 and 2000, we captured and measured male lemurs from Ranomafana National Park in Madagascar 69 times. We used linear and polynomial regressions and residuals to examine the effect of season on GI and the effect of age on GI, after accounting for the effect caused by season among males of breeding age. As the breeding season approached, GI increased significantly, and all individuals measured in both the breeding and nonbreeding season had larger GI values in the breeding season. Among males of breeding age, we found no relationship between age and GI, after accounting for seasonal effects. Age, season and body weight fail to explain the variation remaining in GI. We discuss sperm competition, breeding-group composition, and the presence of parents as additional sources of variation in GI.

Growth, life cycle and fishery biology of Loligo gahi (d’Orbigny, 1835) off the Peruvian coast

The Patagonian squid, Loligo gahi (Cephalopoda: Loliginidae), is a commercially important species of artisanal fisheries on the Peruvian coast. This study aims to provide preliminary information on the life cycle of this species by means of age estimation using statoliths collected in 1997. The gonadosomatic index (GSI) variation during 1996 was also determined in order to ascertain the peak spawning times and to relate hatching and spawning. The specimens were obtained from landings in the artisanal port of Callao in 1996/1997. A statolith was obtained from each of 82 individuals and these were collected, mounted and polished to count microincrements. Growth increments were revealed in the lateral dome of the statolith and were counted using a Carl-Zeiss light microscope at ×400 magnification. The results suggest that the growth model that best fits the data is a power function and that the life span is approximately 1 year. The hatching dates were back-calculated to the spring, summer and autumn months, and showed two main peaks in April and December with a secondary peak in September/October. The GSI variation observed during 1996 revealed a similar secondary peak that was 1 or 2 months earlier.

A comparison of condition factor and gonadosomatic index of sardine Sardinops sagax stocks in the northern and southern Benguela upwelling ecosystems, 1984–1999

Time-series of condition factor (CF) and gonadosomatic index (GSI) were generated using general linear models (GLM) for sardine Sardinops sagax stocks in the northern and southern Benguela ecosystems over the period 1984–1999. During this period the biomass of sardine in the northern Benguela remained at relatively low levels of <500 000 tons, whereas that of southern Benguela sardine increased 40-fold to 1.3 million tons. The GLMs explained 27 and 45% of the observed variation in CF, and 32 and 28% of the observed variation in GSI, for sardine in the northern and southern Benguela subsystems respectively. Whereas the sardine CF in the northern Benguela remained stable over time, that for the southern Benguela stock declined steadily during the study period. Sardine CF showed a seasonal cycle in the southern but not in the northern Benguela. Time-series of GSI showed high interannual variability but no trends in either subsystem, and the seasonal pattern was similar for both stocks. The lack of coherence between the CF time-series for sardine in the two subsystems further suggests that sardine stocks in the northern and southern Benguela subsystems are independent.

Gonadosomatic index (GSI) of female whitefish ( Coregonus lavaretus) in Lake Constance

From 1991 to 1997 the gonadosomatic index (GSI) of pelagic spawning female whitefish ( Coregonus lavaretus, local name “Blaufelchen”) in Lake Constance-Obersee was determined. Average GSI increased from low values in summer to a maximum of about 24% immediately before spawning (end of November/beginning of December). The coefficient of variation of GSI ranged from 14–35% of the mean in summer and autumn and decreased to values between 9 and 16% immediately before spawning. The seasonal increase in GSI was similar for all years investigated, except in 1995, when after an exceptionally mild autumn spawning took place at a water temperature of about 9.4°C. In this year, the post-August development of GSI was retarded compared to the other years of the investigation, but immediately before spawning GSI was at a value of about 24% body weight, i. e. in the same range as in the other years of the study. Despite continuing re-oligotrophication of Lake Constance no decrease in GSI was found during the study period.

Influence of the Reproductive Cycle of Argentinian Hake (Merluccius hubbsi) on Fillet Yield and Operating Costs

Seasonal variations in gonadosomatic index (GSI), in the liver-somatic index (LSI), and in fillet yield of mature hake (Merluccius hubbsi) were investigated. A resting or slow recuperation period and another one of rapid transformation (October-February) were observed in gonads of female hakes. The latter occurred earlier in male fish than in female ones. Spawning took place in March. High LSI values were found after spawning and during the gonadal resting period. Low LSI values together with high GSI values were observed. For the hake filleting operation, yield of weight profile was very similar to that of LSI. A linear correlation was obtained when LSI values were plotted against fillet yield (r2 = 0.818, P < 0.001). The unit cost, as well as the yield, can be linearly correlated with the LSI. This equation allows estimation of the production cost when raw material of equal initial quality in different seasons of the year is processed. The results presented are useful for inventory policies in fish plants.

Reproductive Development of Striped Mullet in Louisiana Estuarine Waters with Notes on the Applicability of Reproductive Assessment Methods for Isochronal Species

We assessed reproductive development of striped mullet Mugil cephulus from the coastal waters of Louisiana. Maturation of primary oocytes began in September of each year, and by October, a synchronous group of homogeneous, vitellogenic oocytes was observed (isochronal development). Based on indirect evidence, spawning occurred from November through early January. Gonadosomatic index (GSI) values varied with size among small, mature female striped mullet, but reached an asymptote for females 330 mm in fork length (FL) and larger. Anomalous development in certain ovaries strongly influenced GSI findings and produced excessively low values. Thus, it is suggested that histological examination be included in this type of reproductive study to identify factors that are responsible for high GSI variation. Potential fecundity correlated moderately well with female size and ranged from 2.7 × 105 to 1.6 × 106 eggs per individual for fish that ranged from 290 mm to 445 mm FL.

Seasonal variations in gonadosomatic index, liver-somatic index and myosin/actin ratio in actomyosin of mature hake ( Merluccius hubbsi)

1. 1. Seasonal variations in gonadosomatic index (GSI), in liver-index (LSI) and in myosin/actin ratio in actomyosin of mature hakes were investigated. 2. 2. A resting or slow recuperation period and another of rapid transformation (October-February) were observed in gonads of female hakes. The latter occurred earlier in male fish than in female ones. Spawning occurred in March. 3. 3. High LSI values were found after spawning and during gonadal resting period. Low hake LSI values with high GSI ones were observed. 4. 4. Myosin/actin ratio profile was very similar to LSI one. A linear correlation was obtained when LSI values were plotted against myosin/actin ratio ones ( r = 0.858, P < 0.01).