Feeding habits of Paralabrax nebulifer (Serranidae) during reproductive and non-reproductive seasons in an adjacent area to Magdalena Bay, Baja California Sur, Mexico

The barred sand bass Paralabrax nebulifer is a commercially important fish off the west coast of Baja California Sur. To assess the diet of this species and variations as a function of sex and reproductive condition, 60 specimens were captured using traps during seven seasonal sampling trips from August 2016 to August 2018 in an adjacent area to Magdalena Bay, Baja California Sur, Mexico. The stomach contents of 50 specimens were obtained (23 males and 27 females). Sex was diagnosed by direct observation of the gonads. Based on the gonadosomatic index, hepatosomatic index, and histological analyses, the reproductive season of the barred sand bass was corroborated for August 2016, April, August, and September 2017, and August 2018, and the non-reproductive season was corroborated for November 2016 and March 2018. The Index of Relative Importance (IRI) was used to classify the main diet components, which comprised three fish species, seven crustacean species, and one mollusk species. According to the IRI, the South American pilchard Sardinops sagax and the red pelagic crab Pleuroncodes planipes were the prey that contributed the most (55%) to the barred sand bass diet. The ANOSIM showed that there were significant differences in the amount and type of prey consumed by sex; the SIMPER analysis revealed that the species contributing the most to differences between the sexes were S. sagax (16.58%), Euphylax dovii (15.95%), Stenocionops ovata (12%), and P. planipes (11.82%) for females. There were significant differences in the amount and type of prey consumed between types of reproductive season; the species contributing the most to differences between seasons were Anchoa spp. (27.76%), and P. planipes for non-reproductive season (22.67%), and S. sagax (11.08%) for reproductive season. The feeding strategy of the barred sand bass was that of a specialist carnivorous predator that fed mainly on the fish Sardinops sagax during the reproductive season, which supply the dietary nutritional requirements of the lipids HUFA (arachidonic acid, 20:4n-6; eicosapentaenoic acid, 20:5n-3; docosahexaenoic acid, 22:6n-3), nutrients required to achieve reproductive success.

Fecundity and Gonadosomatic Index of Sucker Throat Catfish, Pseudecheneis sulcata (McClelland, 1842) from the Snow-fed Tamor River in Eastern Nepal

In comparison to other nations, the Nepalese information on the reproductive biology of hill-stream fish is limited. So, the purpose of the present study was to provide information related to reproductive biology of a hill-stream sucker throat catfish Pseudecheneis sulcata from the snow-fed Tamor River, Nepal. The study was carried out from June 2018 to May 2019. A total of 57 female fish was collected. The fecundity of 22 females was assessed, while the gonadosomatic index was determined using all the collected samples. The absolute fecundity ranged from 2,316 to 7,597 eggs, with an average of 3,660 ± 210. This range of absolute fecundity indicates that Pseudecheneis sulcata is a moderately fecund fish when compared to certain low fecund species and some exceptionally fecund fish with tens of thousands of eggs. Relative fecundity ranged from 65.47 to 129.11 with a mean of 88.98 ± 4.35. The present study demonstrated that absolute fecundity was moderately correlated with total length (r = 0.45) and strongly linked with body weight (r = 0.78), and ovary weight (r = 0.80). Mean gonadosomatic index (GSI) was recorded the highest in January (15.7 ± 1.22%), and showed a decrease in the subsequent month of February (10.3 ± 0.75%), March (6.25 ± 0.28%) and April (1.66 ± 0.40%). The trends of GSI might have indicated that the sucker throat catfish was a batch spawner, with spawning season occuring between January and March.

OVARY DEVELOPMENT, FSH AND LH GENES EXPRESSION OF INDONESIAN LEAFFISH, Pristolepis grootii (Bleeker, 1852), INJECTED WITH LUTEINIZING HORMONE-RELEASING HORMONE ANALOG

Indonesian leaffish, Pristolepis grootii (Bleeker, 1852), is an undomesticated freshwater fish species native to the rivers, flooded swamps, and tributaries of Indonesia. The fish is mainly captured for consumption. In order to prevent its extinction and supply its growing demands, the artificial breeding of the fish should be developed. The purpose of this study was to determine the optimum dose of luteinizing hormone-releasing hormone analog (LHRHa) for stimulating the female P. grootii gonadal development at a dosage of 0, 1, 10, and 50 µg kg-1 of fish. Female fish (20.0 ± 0.6 g) were adapted for 30 days in the rearing environment and then separated into 12 aquariums with six fish per aquarium. Fish were then reared for another 21 days and fed with Tubifex sp. The LHRHa injection was conducted twice on day-7 and 14. Fish bodyweight, gonadosomatic index, gonad histology, blood estradiol-17â, and FSH-â and LH-â gene expression were evaluated at day 0, 7, 14, and 21. The results showed that the injection of the LHRHa hormone stimulated the development of fish gonads and was better achieved with a higher concentration of LHRHa. The best treatment was observed by the administration of 50 µg kg-1 of LHRHa that produced the fastest development among all treatments. This study demonstrated that the LHRHa induction could potentially stimulate the gonadal development of the newly domesticated fish. To our knowledge, this is the first study that reported the success of the induction of female gonad development in the Indonesian leaffish P. grooti.KEYWORDS:

Acaricidal Properties of Bio-Oil Derived From Slow Pyrolysis of Crambe abyssinica Fruit Against the Cattle Tick Rhipicephalus microplus (Acari: Ixodidae)

Slow pyrolysis is a process for the thermochemical conversion of biomasses into bio-oils that may contain a rich chemical composition with biotechnological potential. Bio-oil produced from crambe fruits was investigated as to their acaricidal effect. Slow pyrolysis of crambe fruits was performed in a batch reactor at 400°C and chemical composition was analyzed by gas chromatography-mass spectrometry (GC-MS). The bio-oil collected was used in bioassays with larvae and engorged females of the cattle tick Rhipicephalus microplus. Biological assays were performed using the larval packet test (LPT) and adult immersion test. The GC-MS of crambe fruit bio-oil revealed mainly hydrocarbons such as alkanes and alkenes, phenols, and aldehydes. The bio-oil in the LPT exhibited an LC90 of 14.4%. In addition, crambe bio-oil caused female mortality of 91.1% at a concentration of 15% and a high egg-laying inhibition. After ovary dissection of treated females, a significant reduction in gonadosomatic index was observed, indicating that bio-oil interfered in tick oogenesis. Considering these results, it may be concluded that slow pyrolysis of crambe fruit affords a sustainable and eco-friendly product for the control of cattle tick R. microplus.

A Bayesian Multilevel Ordinal Regression Model for Fish Maturity Data: Difference in Maturity Ogives of Skipjack Tuna (Katsuwonus pelamis) Between Schools in the Western and Central Pacific Ocean

The maturity ogive is vital to defining the fraction of a population capable of reproduction. In this study, we proposed a novel approach, a Bayesian multilevel ordinal regression (i.e., Bayesian continuation ratio model), to model the maturity ogive. The model assumes that the observed maturity stage originates from the categorization of latent continuous variables. We demonstrated this approach by testing whether there are differences in the maturity ogive of skipjack tuna (Katsuonus pelamis) in the western and central Pacific Ocean between two school types, i.e., free-swimming and floating-object-associated schools. The model results show that K. pelamis, given the same fork length, are more likely to have a higher maturity stage in a free-swimming school than those associated with floating objects. The gonadosomatic index revealed the same conclusion. Our results indicate that fish aggregation devices (FADs) could negatively affect the maturity of K. pelamis and consequently reduce the population reproductive potential. This study provides (1) an alternative approach to analyze fisheries ordinal data; (2) important quantitative evidence to evaluate the existing ecological hypotheses; and (3) implications for tuna fisheries management.

Growth pattern, mortality and reproductive biology of common sole, Solea solea (Linneaus, 1758), in the Sea of Marmara, Turkey

The study deals with the growth pattern, mortality, and reproduction of common sole, Solea solea (Linneaus, 1758), from the Sea of Marmara (Turkey). A total of 580 fish specimens were sampled monthly from October 2017 to September 2018. The total length of all sampled individuals ranged from 11.1 to 29.5 cm, corresponding to ages from 1 to 3 years. The length–weight relationship was expressed as W = 0.022 TL2.6838, where the slope indicated negative allometric growth. Growth parameters were L ∞ = 33.7 cm, k = 0.48, and t 0 = −0.18 for all samples. A seasonally oscillating growth model, indicating the amplitude of oscillations, revealed an important seasonal growth pattern. Total, natural, and fishing mortality rates were calculated as 1.42, 0.47, and 1.01, respectively. The exploitation ratio (E = 0.68) indicates that the fishing pressure on the common sole in the Sea of Marmara was high. The sex ratio (♀/♂) was 1.18. The gonadosomatic index (GSI) for females showed that two main spawning seasons were observed: one in spring (May) and one in autumn (September–October). Sizes at the onset of sexual maturity were estimated for both females and males at 21.6 and 18.6 cm, respectively.

Liver Transcriptomic Analysis of the Effects of Dietary Fish Oil Revealed a Regulated Expression Pattern of Genes in Adult Female Spotted Scat (Scatophagus argus)

Despite the significance of n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) in fish oil in promoting the maturation of female broodstocks, the detailed mechanism of the effect on the expression of hepatic reproduction-related genes is still unclear. In this study, transcriptome sequencing was used to analyze the effect of the higher dietary n-3 LC-PUFA level on gene expression in the liver of adult females spotted scat. Two-year-old female spotted scat (average weight, 242.83 ± 50.90 g) were fed with diets containing 8% fish oil (FO) or 8% soybean oil (SO) for 40 days. The fatty acid profile in the serum, liver, and ovary was analyzed, and high proportions of n-3 LC-PUFA were observed in the FO group. The final average fish body weight and gonadosomatic index were similar between the FO and SO groups. The serum vitellogenin (Vtg) and hepatosomatic index (HSI) of the FO group were significantly higher and lower than that of the SO group, respectively. Comparatively, the liver transcriptome analysis showed 497 upregulated and 267 downregulated genes in the FO group. Among them, the expression levels of three estrogen-regulated genes (i.e., Vtga, Vtgb, and Zp4) were significantly higher in the FO than in the SO group. This expression pattern could be related to the upregulation of Hsd17b7 (the key gene for the synthesis of liver steroid hormone) and the downregulation of the Hsp90 (the estrogen receptor chaperone). The expression levels of Foxo1a and Lep, which are involved in the lipid metabolism, decreased significantly in the FO group, which may be related to the lower level of HSI in the FO group. The genes related to liver LC-PUFA absorption and transport, Fabp2 and Mfsd2ab, were significantly upregulated in the FO group, indicating that fish actively adapt to high-fish-oil diets. In brief, high-fish-oil diets can influence the expression of genes related to liver n-3 LC-PUFA metabolism and reproduction, inhibit the accumulation of liver fat, and promote the liver health and gonad development. This study will contribute to clarifying the mechanism of dietary n-3 LC-PUFA on promoting reproductive development in teleost fish.

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

First report on the diet and reproductive biology of red-toothed triggerfish Odonus niger (Ruppell, 1836) from the south-eastern Arabian Sea

The feeding habits and reproductive biology of red-toothed triggerfish Odonus niger (Ruppell, 1836) was analysed from 449 specimens collected from the Karnataka coast of the south-eastern Arabian Sea. Of the total stomachs examined, only 54 (12%) were empty and 395 contained food remains. The diet comprised crustacean remains (48.0%), zooplankton (21.4%), algae (16.5%), fish remains (6.1%) and cephalopod remains (5.3%) along with partially digested matter (2.3%) and detritus (0.4%). The species was found to be a generalist feeder and an omnivore. The overall sex ratio between males and females (1: 0.44) was significantly (P < 0.05) different. Histological examination of the ovaries indicated asynchronous ovarian development in females, with males maturing earlier than females. The gonadosomatic index (GSI) patterns of males and females, and the presence of ripe ovaries and spermatozoids suggested that April–May is the peak spawning period. The absolute and relative fecundity estimates ranged from 16,464–312,420 eggs and 251–2812 eggs g−1 respectively. Fecundity was positively correlated with total length and body weight. The biological information on diet composition and reproductive traits provided for the first time in this study can facilitate conservation, management and sustainable exploitation of this species in the study area.