Biology subjects

Duncan, N. J.

Publications and source records attributed to Duncan, N. J..

4 recordsLinked to original sources

bioRxiv2023

In vivo effect of recombinant FSH and LH administered to meagre (Argyrosomus regius) at the initial stages of sex differentiation.

Recombinant gonadotropins, follicle stimulating (rFSH) and luteinizing hormone (rLH), offer the potential to induce gametogenesis in prepubertal fish. This study aimed to determine the in vivo effect of Argyrosomus regius rFSH (arrFSH) and Argyrosomus regius rLH (arrLH) administered to prepubertal meagre juveniles at the initial stages of sex differentiation. Meagre single-chain recombinant gonadotropins, arrFSH and arrLH were produced with the CHO expression system by Rara Avis Biotec, S. L. Juvenile meagre, 9-months old with mean weight of 222 {+/-} 36 g (mean {+/-} SD) were randomly distributed into seven experimental groups (n = 8 per group) that were treated weekly for three weeks with an acute injection of 6, 12 or 18 g kg-1 of arrFSH (groups, 6-arrFSH, 12-arrFSH and 18-arrFSH) or 6, 12 or 18 g kg-1 of arrLH (groups, 6-arrLH, 12-arrLH and 18-arrLH) or saline solution (Control group). Two more groups (n=8) were set up and treated for 6 weeks, with 12 g kg-1 of arrFSH or saline Control. The fish were held in a 10 m3 tank with natural photoperiod (Feb. - March) and temperature 16.1 {+/-} 0.4{degrees}C. At the start of the experiment (n = 8) and end of the three week experiment all fish were sacrificed and gonads dissected. Gonads were weighed, fixed in Bouins solution and processed for histological analysis. Blood was sampled from all fish at the start and end of the experiment (week 3 and 6) for 17{beta}-estradiol (E2) and 11-ketotestosterone (11-KT) analysis. Juvenile meagre at the start of the experiment were in the initial stages of sexual differentiation, indicated by the presence of the ovarian or testes lumen that was surrounded by undifferentiated embryonic germ stem cells and somatic cells. At the end of the experiment, there was no significant difference in gonadosomatic index (GSI) amongst control (initial and saline treated) and the experimental groups. After three weeks of application of arrFSH, arrLH or saline all fish presented a similar gonadal structure as at the start of the experiment. However, the incidence of isolated developing germ cells (principally spermatogonia, spermatocytes, spermatids, but also perinucleolar stage oocytes) generally increased in arrGTH treated meagre. A mean of 44 % of meagre treated with arrFSH or arrLH presented isolate developing germ cells, mainly male cells. Plasma steroid levels of E2 decreased significantly from the start of the experiments to the end. At the end of the experiment there were no differences in plasma E2 amongst Control fish and rGTH treated fish. Plasma 11-KT showed no change from the start of the experiment to week 3. However, a significant increase was observed in the arrFSH group after six weeks of treatment compared to the start of the experiment and the control group on week 6. The application of arrFSH or arrLH to meagre at the initial stages of sex differentiation did not stimulate steroid production until week six and had a limited, but evident effect on the development of isolated germ cells. The rGTHs, arrFSH or arrLH did not stimulate large developmental changes in undifferentiated gonads. HIGHLIGHTSExogenous recombinant gonadotropins administered to meagre did not advance sexual differentiation. Exogenous recombinant gonadotropins administered to meagre did not affect plasma estradiol. Exogenous recombinant FSH increased the proportion of meagre with isolated male germ cells. Exogenous recombinant FSH increased plasma 11-ketotestosterone in meagre treated for 6 weeks.

physiology↗

bioRxiv2022

A chromosome-level genome assembly enables the identification of the follicle stimulating hormone receptor as the master sex determining gene in Solea senegalensis

Sex determination (SD) mechanisms are exceptionally diverse and show high evolutionary rates in fish. Pleuronectiformes is an emblematic fish group characterized by its adaptation to demersal life and its compact genomes. Here, we present a chromosome-level genome assembly of Senegalese sole, a promising European aquaculture species. We combined long- and short-read sequencing and a highly dense genetic map to obtain a contiguous assembly of 613 Mb (N50 = 29.0 Mb, 99% of the assembly in the n = 21 chromosomes of its karyotype). The correspondence between this new assembly and the Senegalese sole chromosomes was established by fluorescence in situ hybridization with BAC probes. Orthology within Pleuronectiformes was assessed by using the chromosome-level genomes of six important commercial flatfishes covering a broad phylogenetic spectrum of the order. A total of 7936 single-gene orthologues, shared by the six species, were used to identify syntenies in Pleuronectiformes and to explore chromosome evolutionary patterns in the order. Whole genome resequencing of six males and six females enabled the identification of 41 fixed allelic variants in the follicle stimulating hormone receptor (fshr) gene, homozygous in females and heterozygous in males, consistent with an XX / XY chromosome system. The observed association between fshr SNPs and sex was confirmed at the species level in a broad sample, which allowed tuning up a molecular sexing tool. Fshr demonstrated differential gene expression between male and female gonads since 86 days post-fertilization, when the gonad was still an undifferentiated primordium, concomitant with the activation of other testis and ovary marker genes, such as amh and cyp19a1a genes, respectively. Interestingly, the Y-linked fshr allele, which included 24 non-synonymous variants, expressed to a higher level than the X-linked allele at all stages. We hypothesize a molecular mechanism hampering the action of the follicle stimulating hormone that would drive the undifferentiated gonad toward testis.

genomics↗

bioRxiv2021

Feeding habits and the influence of pellet diameter on the feeding responses of the flathead grey mullet (Mugil cephalus) in captivity

The feeding habits and effect of the diameter of pelleted feeds on the feeding responses of wild juvenile and adult flathead grey mullet (Mugil cephalus) in captivity were examined. Optimal pellet size for feeding was defined according to the behavioural responses and ingestion of pellets with different diameters (2, 4, 6, 8 mm) that were dropped into the tank in a random sequence. Larger pellets (6 and 8 mm) were more attractive (lower reaction time, high percentage of capture), but the small to medium-sized pellets (2 and 4 mm) were consumed the most. The optimal size was the 2- and 4- mm pellet diameter for juvenile individuals (365.50 {+/-} 36.90 g; 28.8 {+/-} 0.84 cm) and the 4-mm diameter pellet for adults (937.49 {+/-} 146.54 g; 40 {+/-} 1.12 cm). The preferred feeding area of adult mullet was also studied to estimate preference in relation to pellet characteristics such as floating or sink. Two pellet types, floating or sinking, were offered simultaneously in the water column: at the surface, mid-water column and bottom of the tank. The flathead grey mullet had a preference to feed in the mid-water column and the bottom of the tanks indicating that sinking or slow-sinking pellets would be the optimal feed type in relation to mullet feeding behaviour.

animal behavior and cognition↗

bioRxiv2021

Characterization of the different behaviours exhibited by juvenile grey mullet (Mugil cephalus) under rearing conditions

This research described the common behaviour of grey mullet (Mugil cephalus) under rearing conditions. The different behaviours exhibited by mullets were videorecorded with submersible cameras installed inside of three tanks. A total of 690 minutes per day (07:30 - 18:30 hours) were recorded per tank during a week. Afterwards, an ethogram was elaborated to organize the different behaviours exhibited by juvenile M. cephalus, with two general categories: a) locomotion, including three different observed behaviours (resting, swimming and fast swimming) b) feeding, including three behaviours (surface feeding, bottom feeding and rubbing). The video recordings showed that M. cephalus is a species with a constant locomotion associated to feeding, since they showed constantly movement during most of day light period the opposite to dark periods. Mullets were observed to be a non-aggressive fish species, due to the absence of dominance and aggression towards conspecifics, resulting in a high predisposition for adaptation to captivity. Finally, behavioural frequencies of grey mullets juveniles were not significantly different among the three tanks for most of the behavioural variables analysed (p>0.05) except for the variable bottom feeding (p=0.02). Results from this study could be of interest to the aquaculture industry to implement protocols and to optimize rearing techniques for the production of grey mullet.

animal behavior and cognition↗