Mackerel (Scomber australasicus) Reproduction in Northeastern Taiwan

Blue mackerel (Scomber australasicus) is a crucial target species for coastal fisheries in Taiwan, and additionally it has maintained its status as the highest-produced species. The timely measurement of spawning status is crucial for determining the correct management strategy for this species. The objective of this study was to determine size at maturity, fecundity, batch fecundity, and spawning frequency on the basis of samples collected from Nan-Fang-Ao fishing port in Yilan, during the spawning season from 2017 to 2019. Histological sections indicated that the blue mackerel were multiple spawners; a higher percentage of female fish spawned at the peak of the gonadosomatic index. The 50% sizes at maturity were 32.02, 32.13, and 29.64 cm. Mean total fecundity (batch fecundity) was 165 (103), 229 (96), and 210 (68) oocytes per ovary-free weight (g) for 2017, 2018, and 2019, respectively; fecundity was determined through observation of postovulatory follicles (POFs). The spawning frequencies (spawning fraction) in 2017, 2018, and 2019 were 3–10 days (0.13), 4–14 days (0.08), and 4–12 days (0.09), respectively. The spawning frequencies determined through the three estimated methods, namely the sums of (a) hydrated and Day 0 POFs; (b) Day 1+ POFs, and (c) all data combined, were 1 spawning event per 8, 10, and 9 days, respectively. The reproduction of the blue mackerel was greater in 2017 than it was in 2018 or 2019, as indicated by the higher batch fecundity and shorter spawning seasons. Environmental factors should also be considered as a major factor influencing successful reproduction and spawning season

Blue Cod, Parapercis Colias, Maturity, Fecundity, Sex Change, and Potential Drivers of Sex Ratio in The Marlborough Sounds

<p>Blue cod, Parapercis colias (Pinguipedidae), are widely considered to be the most important recreational finfish species in the South Island. However, blue cod have been declining in abundance in the Marlborough Sounds for many years, and currently, sex ratios are highly male- biased. Blue cod are believed to be a socially structured hermaphroditic species whose populations are prone to local depletion. A potting survey in the Marlborough Sounds was carried out by NIWA in 2013, and along with environmental measurements, 3247 blue cod were measured, weighed, sexed, and stage of sexual maturity was classified macroscopically at sea. Gonads from a subsample of these fish were removed and preserved. In Chapter Two, the preserved gonads were processed histologically and a species-specific histological maturity key was developed. Histological and macroscopic maturity classifications and length-at-maturity estimates were compared. Additionally, estimates of spawning frequency and batch fecundity were made using histological and gravimetric methods. In Chapter Three, possible drivers of sex ratio were investigated using the survey data. Density, large male influence, and environmental factors were considered. In Chapter Four, the feasibility of using digital imaging software to age blue cod otoliths was investigated using the OtolithM application in ImagePro Premier. There was poor agreement between macroscopic and histological maturity classifications (20%, overall). Macroscopic methods overestimated the proportion of mature fish at length in the larger sample, which led to biased length-at-50% maturity (L₅₀) estimates. Macroscopic L₅₀ estimates differed markedly from histology estimates. Using histological data, male L₅₀ was 26 cm TL. Histology indicated that there was no length at which 100% of females were mature. Therefore, a three-parameter capped logistic model was used. Histologically, female L₅₀ was 23.6 cm TL, and the Cap was 0.78, indicating the proportion of mature females reached an asymptote at 0.78. Spawning frequency was 4.6 days, and mean relative batch fecundity was 6.5 hydrated oocytes per gram body weight (SD = 3.3). Hermaphroditism was confirmed for blue cod and was macroscopically identifiable. The analyses in Chapter Three indicated that density had some effect on sex ratio, and large males influenced local sex ratios. Finally, the imaging software could not accurately estimate age compared to an expert reader, and it produced highly variable age estimates. This research found that the macroscopic maturity classifications for blue cod were inaccurate, and revision of the macroscopic key is suggested. The biased estimates of L₅₀ from macroscopic data could lead to biased estimates of spawning stock biomass (SSB). Batch fecundity was markedly lower than the previously reported estimates. The finding of a macroscopically identifiable hermaphroditic stage suggested that ‘hermaphrodite’ should be added as a sex class in the macroscopic key. From the GLM in Chapter Three, in more dense populations, the proportion of males increased. This may have been from changes to male mating strategies, or density may influence the occurrence of primary and secondary males. Finally, areas with males > 45 cm TL had a higher proportion of females, suggesting that large males should be protected in order to help balance sex ratios.</p>

Blue Cod, Parapercis Colias, Maturity, Fecundity, Sex Change, and Potential Drivers of Sex Ratio in The Marlborough Sounds

<p>Blue cod, Parapercis colias (Pinguipedidae), are widely considered to be the most important recreational finfish species in the South Island. However, blue cod have been declining in abundance in the Marlborough Sounds for many years, and currently, sex ratios are highly male- biased. Blue cod are believed to be a socially structured hermaphroditic species whose populations are prone to local depletion. A potting survey in the Marlborough Sounds was carried out by NIWA in 2013, and along with environmental measurements, 3247 blue cod were measured, weighed, sexed, and stage of sexual maturity was classified macroscopically at sea. Gonads from a subsample of these fish were removed and preserved. In Chapter Two, the preserved gonads were processed histologically and a species-specific histological maturity key was developed. Histological and macroscopic maturity classifications and length-at-maturity estimates were compared. Additionally, estimates of spawning frequency and batch fecundity were made using histological and gravimetric methods. In Chapter Three, possible drivers of sex ratio were investigated using the survey data. Density, large male influence, and environmental factors were considered. In Chapter Four, the feasibility of using digital imaging software to age blue cod otoliths was investigated using the OtolithM application in ImagePro Premier. There was poor agreement between macroscopic and histological maturity classifications (20%, overall). Macroscopic methods overestimated the proportion of mature fish at length in the larger sample, which led to biased length-at-50% maturity (L₅₀) estimates. Macroscopic L₅₀ estimates differed markedly from histology estimates. Using histological data, male L₅₀ was 26 cm TL. Histology indicated that there was no length at which 100% of females were mature. Therefore, a three-parameter capped logistic model was used. Histologically, female L₅₀ was 23.6 cm TL, and the Cap was 0.78, indicating the proportion of mature females reached an asymptote at 0.78. Spawning frequency was 4.6 days, and mean relative batch fecundity was 6.5 hydrated oocytes per gram body weight (SD = 3.3). Hermaphroditism was confirmed for blue cod and was macroscopically identifiable. The analyses in Chapter Three indicated that density had some effect on sex ratio, and large males influenced local sex ratios. Finally, the imaging software could not accurately estimate age compared to an expert reader, and it produced highly variable age estimates. This research found that the macroscopic maturity classifications for blue cod were inaccurate, and revision of the macroscopic key is suggested. The biased estimates of L₅₀ from macroscopic data could lead to biased estimates of spawning stock biomass (SSB). Batch fecundity was markedly lower than the previously reported estimates. The finding of a macroscopically identifiable hermaphroditic stage suggested that ‘hermaphrodite’ should be added as a sex class in the macroscopic key. From the GLM in Chapter Three, in more dense populations, the proportion of males increased. This may have been from changes to male mating strategies, or density may influence the occurrence of primary and secondary males. Finally, areas with males > 45 cm TL had a higher proportion of females, suggesting that large males should be protected in order to help balance sex ratios.</p>

Reproduction and fecundity of invader of internal insemination Trachelyopterus galeatus in a Neotropical floodplain

After the formation of Itaipu Reservoir, the invader Trachelyopterus galeatus colonized the upper Paraná River. Light microscopy was used to describe gametogenesis and the reproductive phases of females and males. The following data were verified: diameter of the oocytes, spawning type, batch fecundity by ovary weight, standard length, and total weight of the fish, along with the regions where this species reproduced in the upper Paraná River floodplain. A total of 470 specimens were collected quarterly in 2016, 2018 and 2019, and bimonthly in 2017. The gonads were fixed in a Karnovsky solution, dehydrated, infiltrated, and embedded in historesin. The histological slides were stained using PAS + iron hematoxylin + metanil yellow, analyzed and photographed under an image-capturing microscope. As regards diameter of the oocytes and fecundity estimates, ovaries whose oocytes were measured under a stereomicroscope were sampled. In the oogenesis, undifferentiated and differentiated oogonia, early primary growth oocytes, secondary growth oocytes, full-grown oocytes and maturing oocytes were recorded. In the spermatogenesis, primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa were recorded. The reproductive phases found for females and males were: immature, early development, late development, spawning/sperm-releasing capable, regression, and regeneration. Trachelyopterus galeatus prefers to occupy and reproduce in the Ventura, Patos, Guaraná, Fechada, Garças, and Pau Véio lagoons. The diameter of the oocytes varied from 0.4 to 2.9 mm. Females spawn, on average, 113 oocytes per batch. Batch fecundity variation shows that the larger the ovary, standard length, and total weight, the larger the number of oocytes to be spawned. This invader possesses reproductive success in the upper Paraná River floodplain, especially in lagoons.

Ovarian dynamics, batch fecundity and spawning phenology of the lessepsian migrant Etrumeus golanii DiBattista, Randall & Bowen, 2012 (Clupeidae: Dussumieriinae)

The Golani’s round herring Etrumeus golanii is an Erythraean small pelagic fish (lessepsian migrant) that entered into the Mediterranean Sea through the Suez Canal. It has expanded its distribution from the east to the western Mediterranean with well-established local populations. We investigated basic aspects of its reproductive biology off the island of Crete (eastern Mediterranean) using ovarian histology and analysis of oocyte size-frequency distributions. The species exhibited a protracted breeding period (winter to early summer), with all ovaries examined during the main spawning season having markers of recent (postovulatory follicles, POFs) or imminent spawning (advanced oocyte batch in germinal vesicle migration or hydration). The advanced batch (AB) increased rapidly in size and was fully separated from the remainder, less developed oocytes in 95% of females with “old” POFs (POFs with signs of degeneration) and all females in final maturation. The growth of the subsequent batch (SB) was arrested at sizes <630 µm until full maturation of the AB. Mean diameter of hydrated oocytes ranged from 1181 to 1325 µm and relative batch fecundity was low ranging from 56 to 157 eggs g-1. The simulation of a coupled hydrodynamic/biogeochemical model (POM/ERSEM) provided evidence that E. golanii takes advantage of the seasonal cycle of planktonic production to reproduce and exhibits monthly changes in batch fecundity that appear to be closely related with the seasonal cycle of mesozooplankton concentration.

REPRODUCTION ASPECTS OF COBIA CAUGHT IN PERNAMBUCO COAST, NORTHEASTERN BRAZIL

Aspects of the reproduction of cobia (Rachycentron canadum) population from the coast of Pernambuco State, Northeastern Brazil, were studied from February 2004 to August 2006. One hundred eleven individuals were analyzed: 54 females with fork length (FL) ranging from 40 to 137 cm (mean ± standard deviation: 90.7 ± 18.1 cm) and 57 males with FL from 43 to 114.5 cm (82.4 ± 17.0 cm). Histological analysis was used to identify maturational phases. Spawning capable females were found from August to May, except in December, while mature males were present throughout the year, except in July. Size at first maturity (L50) obtained by Bayesian analysis was 72.51 cm FL for females and 60.69 cm FL for males. Overall batch fecundity ranged from 192,063 to 1,600,513 oocytes (722,398 ± 430,911) and mean relative batch fecundity ranged from 32.9 to 104.8 (71.1 ± 29.8) oocytes per gram of female body weight. The data indicate that the reproduction of cobia off the coast of Pernambuco occurs throughout the year, but with peaks between February and April, period in which gonadosomatic indices reach the maximum values and then decrease until May for females and males.

The reproductive potential of yellowfin tuna (Thunnus albacares Bonnaterre, 1788) caught in the eastern part of the Indian Ocean

Knowledge of reproduction biology provides valuable information to better understanding population dynamics, including a population's resilience to fishing. The yellowfin tuna reproductive biology in the eastern Indian Ocean was studied by analyzing some essential characteristics: size at maturity, the spawning season, frequency of spawning, egg diameter, and batch fecundity. From 2018 to 2020, 206 female yellowfin tuna were sampled (23-170 cmFL). They were using histological and morphological analysis, resulting in the size at maturity (Lm50) of yellowfin tuna being 92.73 cmFL. The spawning season of yellowfin tuna occurred between September and May, spawning every 1.55 days within the spawning period. The oocytes size ranged between 27.1 – 570.5 μm, and the mean size of oocytes (mean ± standard deviation) was 189.5±129.4 μm. The mean batch fecundity was 3.1±1.7 million oocytes, and the mean relative batch was 82.4±38.4 oocytes gram-1 of GGT weight. The uncertainties in current yellowfin stock assessment models can be reduced by providing complete information on the reproductive traits in the region to achieve a sustainable fishery.

A first assessment of atresia in the Chilean jack mackerel Trachurus murphyi (Teleostei, Carangidae) from the South-eastern Pacific Ocean

The Chilean jack mackerel Trachurus murphyi support an important fishery in the South-eastern Pacific Ocean and has declined considerably over time. T. murphyi have asynchronous ovarian development with an oceanic spawning (September to January). Despite the economic importance of this resource critical issue such as characteristics and dynamics of atresia, which affect the reproductive output, are unknown. Females of T. murphyi caught in different spawning seasons were analysed to describe patterns of prevalence and intensity of atresia. General linear models (GLM) were performed by using prevalence and intensity atresia as response variables and gonadosomatic index, condition factor, sea surface temperature, postovulatory follicles and month/year as explanatory variables. The batch fecundity and relative fecundity were compared between females showing atresia, postovulatory follicles and non-atretic females. The stages of atresia identified were alpha, beta and gamma. The GLM showed that variations in the prevalence and intensity of atresia were explained for all variables, except condition factor for prevalence, and gonadosomatic index for intensity of atresia. According to our results, the dynamic of alpha and beta atresia could be considered a potential proxy for any disruption of spawning season. The batch fecundity and relative fecundity were lowest compared with other Trachurus spp. This is the first assessment comparing fecundity between atretic and not atretic females for this species.