Estimation of Important Reproductive Parameters for Management of the Shoemaker Spinefoot Rabbitfish (Siganus sutor) in Southern Kenya (original) (raw)
Related papers
The Shoemaker spinefoot, Siganus sutor, is a member of the family Siganidae, commonly known as rabbitfish. Many demersal fish populations in the Kenyan waters are heavily exploited, and fishing effort may be above optimum levels for some species. This study was aimed at determining missing parameters on spawning periodicity and maturity of S. sutor for the Kenyan south coast area of Msambweni, complementing a suite of parallel studies on spawning aggregation based fisheries for this species. A total of 376 samples were collected over 12 months, including 85 that were collected over four lunar phases in November and December 2010. Monthly GSI showed two distinct peaks, one in June and July and one in November and January, suggested two distinct spawning periods within the year. The highest GSI was recorded in November while the lowest values occurred in April August and September. A lunar pattern in ovarian development stage was seen with the highest proportion of ripe ovaries (RI) observed in the full moon phase, whereas running ripe (RR) or hydrated ovaries dominated samples in the last quarter. Imminent spawning was confirmed by the presence of hydrated oocytes and post ovulatory follicles, observed primarily during the last quarter and to a lesser extent during full moon. GSI value Kruskal-Wallis test showed significant differences in GSI between moon phases (p<0.05). In conclusion, histological analysis of ovaries points to synchronous development of oocytes with moon phases, suggest that their release takes place over short period of time after the full moon.
Fisheries Science, 2001
This study clarifies the annual reproductive cycle and the lunar-synchronized spawning of the spiny rabbitfish (Siganus spinus) that inhabit the Okinawan waters. Annual and weekly changes in the gonadosomatic index (GSI) and the histological features of the ovaries were checked. Gonadosomatic index was high during the months of May to July, and yolk-laden oocytes were observed in the ovaries from March to July. Some of the ovaries collected during June and July contained oocytes at maturation stage or ovulatory follicles. These results suggest that the spiny rabbitfish undergo active vitellogenesis and spawning from May to July. During the reproductive season (May to July), collection of fish according to the lunar phase revealed that a high GSI occurred around the time of the new moon. Cyclic oocyte development with peaks around the time of the same moon phase was also observed, suggesting that, in Okinawan waters, this species is a lunar-synchronized spawner and spawns three times.
International Journal of Marine Science, 2012
The Shoemaker spinefoot, Siganus sutor, is a member of the family Siganidae, commonly known as rabbitfish. Many demersal fish populations in the Kenyan waters are heavily exploited, and fishing effort may be above optimum levels for some species. This study was aimed at determining missing parameters on spawning periodicity and maturity of S. sutor for the Kenyan south coast area of Msambweni, complementing a suite of parallel studies on spawning aggregation based fisheries for this species. A total of 376 samples were collected over 12 months, including 85 that were collected over four lunar phases in November and December 2010. Monthly GSI showed two distinct peaks, one in June and July and one in November and January, suggested two distinct spawning periods within the year. The highest GSI was recorded in November while the lowest values occurred in April August and September. A lunar pattern in ovarian development stage was seen with the highest proportion of ripe ovaries (RI) observed in the full moon phase, whereas running ripe (RR) or hydrated ovaries dominated samples in the last quarter. Imminent spawning was confirmed by the presence of hydrated oocytes and post ovulatory follicles, observed primarily during the last quarter and to a lesser extent during full moon. GSI value Kruskal-Wallis test showed significant differences in GSI between moon phases (p<0.05). In conclusion, histological analysis of ovaries points to synchronous development of oocytes with moon phases, suggest that their release takes place over short period of time after the full moon.
Journal of Fish Biology, 2010
Reproduction was investigated in relation to lunar and annual cycles in a population of yellow tang Zebrasoma flavescens, a popular aquarium species commercially harvested in Hawaii. Lunar periodicity was determined to be an inherent characteristic of reproduction; peaks in mean daily egg production, female gonado-somatic index (I G) and the fraction of females with eggs were observed at the full moon of each sampled month. An increase in the fraction of late-stage vitellogenic oocytes within the ovaries was also observed at the full moon. Reproductive effort peaked in the late spring and summer as indicated by high values of mean daily egg production, female I G and the recorded incidence of females spawning for at least two consecutive days. Mean daily egg production and I G of monthly samples were lowest in November to February, although some level of egg production continued throughout the year. Large individual variation in batch fecundity was observed, with a range from 44 to >24 000 eggs per female produced on a single sampling date. Smaller females, 80-120 mm standard length (L S), produced limited numbers of eggs, while females ≥120 mm L S were capable of maximal egg production (>20 000 eggs per batch). In contrast to trends observed in many fish species, no significant relationship between batch fecundity and adult L S > 120 mm was observed in female Z. flavescens. An estimate of annual fecundity (mean ± s.e. 1 055 628 ± 120 596 eggs) was also generated using a simple model of the lunar variability in egg production. This study illustrates the importance of accounting for potential variation in egg production over time, especially with respect to diel and lunar cycles, in the design of reproductive studies of multiplespawning fishes. Greater insight into the environmental factors that regulate reproductive activity may be gained by determining the relative reproductive investment allocated at each spawning event. The ability to estimate annual fecundity for more multiple-spawning species will facilitate examination of the effects of fishing on the reproductive characteristics of these populations and permit examination of life-history evolution across a broader suite of fishes.
Asian Journal of Biological Sciences Research Article, 2019
Background and Objective: Rabbitfish Siganus rivulatus is one of the ecologically and commercially important marine fish inhabiting Egyptian northwestern Mediterranean Coastal regions. Studying the reproductive biology of fish species is among the most important life-history parameters that researchers must establish. The present study was carried out to test the theory of variation in the reproductive biology of rabbitfish Siganus genus and determine the exact spawning season of Siganus rivulatus species. Material and Methods: Random monthly samples of wild fresh dead fish were collected from Alexandria (December, 2016 to November, 2017). Biometric measures (total length, weight, gutted weight and ovary weight) were carried out. The fish was dissected and ovarian samples were collected and weighed monthly (average n = 20) throughout the year to identify the macroscopic and microscopic features of different maturity stages, determine gonadosomatic index values and fecundity. Results: Monthly analysis of the maturity stages distribution and gonadosomatic index recognized one distinct peak in June, identifying the spawning season (late May to mid of July). The morphological appearance and histological examination of the ovaries together with the ultrastructural changes in the oocytes wall showed that this species is an annual synchronous oocyte developer and their release takes place over a short period. Conclusion: Siganus rivulatus has a short spawning period extending from late May to mid of July (the current study) with an annual seasonal variation depending on different environmental factors. This study recommends the determination of the exact timing of the spawning season for this fish species annually as a basic mariculture practice due to its ecological and economical implication.
Aquaculture Research, 2012
This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in preovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and di¡erent oil droplet coalescence rates. This categorization covered seven stages (from I to VII)^from the end of vitellogenesis to ovulation. The categorization was veri¢ed by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 1C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coe⁄cient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ine¡ective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical di¡erences were found in terms of latency time between experimental groups at di¡erent maturity stages (II^789 8 h; III^57^78 h; IV^48^58 h; V^32^49 h; VI^5^30 h) according to the proposed classi¢cation. This classi¢cation and the results presented in the study signi¢cantly improved the synchronization of ovulation, which may positively a¡ect the e¡ectiveness of pikeperch production under controlled conditions.
Contrasting post-ovulatory follicle production in fishes with different spawning dynamics
Fisheries Research, 2020
The assessment of postovulatory follicles (POFs) is of considerable importance when applying the Daily Egg Production Method (DEPM) since it is used to estimate both spawning frequency (S) and batch fecundity (F B), provided that daily cohorts of POFs are discernible. Atlantic sardine (Sardina pilchardus) and Atlantic mackerel (Scomber scombrus), two commercially valuable pelagic species with different spawning dynamics were investigated principally to evaluate the appropriateness of the POF method to properly reflect S and F B. For appropriate quantification, both the Weibel and the postovulatory follicles packing density (POFPD) method, the latter described in this paper, were applied and compared. In sardine, not only was the existence of one single daily POF cohort confirmed but also the estimated number of POFs in the cohort matched gravimetric F B results. Furthermore, the Weibel method and POFPD led to similar results. However, several daily POF cohorts cooccurred in the mackerel ovary. Therefore, POF-based estimation of F B only works for species such as sardine with a single, daily POF cohort. Likewise, in relation to estimation of S, the occurrence of single versus multiple POF cohorts makes the histological assignment of spawners to daily spawning classes either straightforward or difficult for species comparable to sardine or mackerel, respectively. In the latter case we suggest focusing in the largest, thus newest, POFs which correspond to the latest spawning event. Therefore, the appropriateness of the POF method in applications of the DEPM should be judged based on the spawning dynamics of the assessed species.
Investigations on the ovarian cycle of fish species that inhabit Hungarian rivers are necessitated by both environmental and economic reasons. The objective of our research was to explore new fundamental knowledge concerning the ovarian cycle of the white bream (Blicca bjoerkna, Linnaeus, 1758), barbel (Barbus barbus, Linnaeus, 1758), orfe (Leuciscus idus, Linnaeus, 1758) and nase (Chondrostoma nasus, Linnaeus, 1758). Histological investigation of ovaries and determination of proportions of oocytes in different stages of development is an appropriate method for the description of spawning characteristics of these species. Our results show that the GSI value for all four investigated species starts to increase at the end of summer and reaches its maximum before spawning. In the barbel and white bream, the presence of oocytes in the stage of cortical alveoli and the heterogeneous size of oocytes in the stage of vitellogenesis in the pre-spawning period indicate that barbel and white bream are multiple spawners. In contrast, in the orfe and nase, the absence of oocytes in the stage of cortical alveoli and the homogeneous size of cells in the stage of vitellogenesis indicate that orfe and nase are single spawners.