Neuroendocrine regulation of puberty in fish: insights from the grey mullet (Mugil cephalus) model

We investigated the molecular regulation of pubertal development in the grey mullet, Mugil cephalus, a relatively late-maturing teleost fish. We have isolated and characterized the cDNAs of key reproductive genes along the brain-pituitary-gonadal (BPG) axis as well as the promoters of genes that modulate the axis at multiple levels. Together with relevant findings from other model species, we propose a conceptual model of the neuroendocrine regulation of puberty in the female grey mullet. Research areas that warrant further investigation are identified in the model.     

Fishery, seasonal abundance and mortality of grey mullets (Pisces: Mugilidae) in Negombo Lagoon, Sri Lanka

The seasonal abundance and instantaneous natural and fishing mortalities of six species of grey mullets, namely Liza subviridis, L. macrolepis, L. tade, Mugil cephalus, Valamugil buchanani and V. cunnesius were studied as a prelude for the management of their fishery in Negombo lagoon (7°10′N and 79°50′E). L. subviridis was the most abundant of the grey mullet species in the commercial catches and accounted for 37% of the total grey mullet catch. M. cephalus was the least abundant and constituted 6%. The annual catch of grey mullets was estimated to be around 23 000 kg (5.67 kg/ha); about 40 % of the total fish landings of the lagoon. The seasonal variation in the catch of different species of grey mullets appear to be related to their breeding seasons and spawning migrations. The highest value for instantaneous natural and fishing mortalities, which were 1.04 and 0.94 respectively were obtained for V. cunnesius. The lowest values for instantaneous natural and fishing mortalities which were 0.51 and 0.19 respectively were obtained for M. cephalus. The exploitation ratios calculated were less than 0.5 for all species other than L. tade which suggest that the grey mullet populations excluding L. tade in this lagoon may presently be underexploited.     

Ichthyophonus infections in cultured marine fish from Spain

Ichthyophonus sp. is reported for the first time in Mugil capito (thinlip grey mullet) and Li a saliens (leaping grey mullet). The fungus was also found in L. aurata (golden grey mullet), Dicentrarchus labrax (sea bass), Sparus aurata (gilthead sea bream) and Scophthalmus maximus (turbot), whereas Mugil cephalus (grey mullet) was not parasitized. In fish sampled periodically, the highest prevalences were observed in sea bass and the lowest in turbot. Among the fish sampled occasionally, the fungus was found associated to an epizootic in thinlip grey mullet. Ichthyophonus was never found in fish weighing <0·5 g. An increase in the prevalence of infection with the age of turbot and gilthead sea bream was observed. Gilthead sea bream and sea bass showed higher prevalences in a closed system than in open and semi-intensive systems. Multinucleate spherical spores, hyphae and endospores of Ichthyophonus sp. parasitized different organs of thinlip and leaping grey mullets, though infection intensity was maximal in the spleen. In the remaining fish, the fungus was found mainly in the trunk kidney, where it appeared frequently in a necrotic form. Ichthyophonus sp. can be considered a potential threat for marine fish aquaculture, especially in culture conditions which may favour the introduction and transmission of the fungus.     

Studies on the chemical biology of young grey mullet, Mugil cephalus L.

The chemical composition of tank and pond reared and wild young grey mullet, Mugil cephalus L., ranging in length from 15 to 75 mm was studied. Tank reared mullet had a higher percentage of protein, carbohydrate, total lipid and a lower moisture content than wild fish. These differences are attributed to the artificial diet, available in excess, as well as the relatively inactive life in the confined spaces of the rearing tanks. M. cephalus in general has a high percentage of total lipid and therefore, can be classified as a 'fatty' fish. The highest level of protein in tank reared fish was found in those kept at a salinity of 20‰. Fish reared on an excess diet in fresh water tended to show a close similarity to wild fish in trends of change of chemical constituents with growth.     

鲻鱼的染色体组型研究

本文采用体内注射ＰＨＡ制备肾细胞染色体标本的方法，对鲻鱼的染色体组型进行了研究，其结果２ｎ＝４８，ＮＦ＝４８，型公式为４８ｔ。     

盐度胁迫对鲻鱼幼鱼鳃丝Na+/K+-ATP酶活力 和体含水量的影响

研究了环境盐度急性胁迫对鲻鱼幼鱼(Mugil cephalus)鳃丝Na+/K+-ATPase(NKA)活性及体内含水量的影响.结果表明,将幼鱼从S33(盐度33)的对照组中直接转移至S0(盐度0)、S10(盐度10)、S20(盐度20)、S33和S40(盐度40)的水体中,随盐度降低各盐度处理的死亡率迅速升高.各处理...     

FIRST REPORT OF GYMNODINIUM PULCHELLUM (DINOPHYCEAE) IN NORTH AMERICA AND ASSOCIATED FISH KILLS IN THE INDIAN RIVER, FLORIDA

Fish and invertebrate kills were reported from September to October 1996 in the Indian River, Florida, coincident with blooms of the dinoflagellate Gymnodinium pulchellum Larsen 1994. This is the first report of a bloom of this species in the Americas. Fish and invertebrate species affected were common snook ( Centropomus undecimalis ), striped mullet ( Mugil cephalus ), hardhead catfish ( Arius felis ), red drum ( Sciaenops ocellatus ), sheepshead ( Archosargus probatocephalus ), black drum ( Pogonias cromis ), blue crab ( Callinectes sapidus ), and shrimp ( Penaeus spp.). However, Gymnodinium pulchellum has previously caused fish kills in Japan and Australia. Examination of archived phytoplankton samples from a fish kill reported in the same area of the Indian River in August 1990 confirmed the presence of high concentrations of G. pulchellum. Fish kills associated with Alexandrium monilatum and potentially Pfiesteria -like species in the Indian River also are discussed. Scanning electron microscopy provided additional morphological detail on this distinct but little-known dinoflagellate.     

Aspects of the biology of grey mullet, Mugil cephalus L., adult populations of a coastal lagoon in Sri Lanka

The biology of grey mullet, Mugil cephalus L., adult populations in a coastal lagoon in Sri Lanka is presented. The percentage of grey mullet catches increased with increasing salinity. The larger fish were found in the deeper areas and the relationship of total length to depth was L = 8.4602e^{0.0058 D} where L = total length and D = depth (cm). The overall female to male ratio was 0.95 : 1.0 and seasonal variation in the sex ratio is considered to be caused by the differential timing in the spawning migrations of the two sexes. Males mature at 34.0 cm and females at 31.5 cm. The main spawning season was between January and May and it is hypothesized that the breeding season is geared to utilize the favourable time period, for growth of fry, in the lagoon. Grey mullet sheds its eggs in batches. Fecundity varied from 0.45 to 4.2 million in fish ranging in length from 32 to 56 cm and in weight from 0.7 to 2.2 kg. Fecundity was significantly correlated to body length and weight and gonad weight.     

Isolation and characterization of visceral excitatory neuropeptides from striped mullet (Mugil cephalus L.) brain

From a brain extract of the catadromous fish, striped mullet (Mugil cephalus), two visceral excitatory neuropeptides (Mvp-1 and Mvp-2) were isolated by means of reversed phase chromatography together with bioassay on fish hindgut. The primary structure of Mvp-1 was elucidated to be SGPAGVLamide by ESI-Q-TOF mass spectrometry. The threshold concentration of Mvp-1 that changes spontaneous contraction of mullet hindgut was between 10(-9) and 10(-8) M. In addition, Mvp-1 was found to exert excitatory activities on some other smooth muscle segments (oviduct and esophagus) of mullet but it did not show any effect on body wall muscle strips. Therefore, the present study suggests that Mvp-1 and Mvp-2 peptides act as factors that control visceral contractions of mullet gastrointestinal tract.     

Aetiology of 'red spot' disease (vibriosis) with special reference to the ectoparasitic digenean Prototransversotrema steeri (Angel) and the sea mullet, Mugil cephalus (Linnaeus)

The ectoparasitic digenean trematode Prototransversotrema steeri was observed to infect a wide range of estuarine fish species of southern Queensland. The intensity and incidence of trematode infections on Mugil cephalus hosts were recorded and appeared to alter with the estuarine movement of the sea mullet host.
Highest trematode population densities were present on post-spawning M. cephalus which had recently traversed brackish estuarine waters. Similarly, the highest prevalence of external 'red spot' lesions was also recorded from such fish.
The degree of complicity between P. steeri and 'red spot' bacterial pathogens was examined and is discussed. 'Red spot' or 'ulcer disease' is presented as a disease of multiple aetiology. It is suggested that some ectoparasites and a variety of primary and secondary bacterial pathogens may interact with environmental and behavioural factors to determine the prevalence of external lesions within each affected fish species.     

Effects of 17α-methyl-testosterone on spermatogenesis and spermiation in the grey mullet, Mugil cephalus L.

Diets containing 17α-Methyl-testosterone were given to grey mullet, Mugil cephalus , during the refractory period in its reproductive cycle at the dosage of 25 mg or 12.5mgkg⁻¹ fish. Fish in experiment I were fed the diet containing methyl-testosterone every day for 55 weeks, and fish in Experiment II were fed the same diet daily for the first 10 weeks, and three times per week for the next 42 weeks. Fish were checked for the presence of sperm weekly or bi-weekly and tested for fertility during the spawning season. Terminal gonad weights and histology were compared with control groups. This study demonstrated that male mullet will mature 3 weeks or less by oral administration of 12.5 mg methyl-testosterone kg⁻¹ fish daily. Fish can then be maintained in mature condition by feeding them methyl-testosterone at 12.5 mg kg⁻¹ three times per week.     

Larvae of Contracaecum sp. among inshore fish species of southwestern Australia

Larval nematode infections were investigated in 236 fish from 17 estuarine and near-shore species in southwestern Australia. Larvae of the genus Contracaecum were found in 4 species of fish (Acanthopagrus butcheri, Sillaginodes punctata, Mugil cephalus and Aldrichetta forsteri). The prevalence and intensity of infection was highest in the 2 species of mullet: 81% infected and 9.8 +/- 1.5 larvae fish(-1) for M. cephalus; 100% and 12.7 +/- 3.7 larvae fish(-1) for A. forsteri. There was no evidence of post-mortem migration of worms from the visceral organs to the musculature of the fish.     

Comet assay using mullet (Mugil sp.) and sea catfish (Netuma sp.) erythrocytes for the detection of genotoxic pollutants in aquatic environment

The development of comet assay for aquatic organisms is of particular relevance in light of the importance of coastal fisheries to several countries around the world. Two of the most common fish species native to southern Brazil are the gray mullet (Mugil sp.) and sea catfish (Netuma sp.) for which we have produced a standardized comet assay using whole erythrocytes taken from samples of these fish. We investigated the potential of the comet assay for monitoring genotoxicity in mullet and sea catfish and made a preliminary investigation of the baseline levels of DNA damage in the erythrocytes of samples of these fish from non-polluted areas as well as assessing the in vitro sensitivity of erythrocyte exposed to 2, 4 and 8 x 10(-5) M of methyl methanesulfonate (MMS) for 1, 2, 6 and 24h at 25 and 37 degrees C. Our results show that there was an increase in baseline DNA damage at higher temperatures and that the amount of MMS-induced DNA damage also increased at higher temperatures and that there was a clear dose/time response to treatment with MMS. To assess the possibility of using fish for environmental biomonitoring we also used the comet assay to investigate the in vitro genotoxic effect of MMS on whole blood cells from human donors and found a clear concentration-related effect at all exposure times, findings which agree with those of other workers. This study demonstrates the potential application of the comet assay to erythrocytes of mullets and sea catfish. However, these findings also suggest that temperature could alter both baseline DNA damage in untreated animals and in vitro cell sensitivity towards genotoxic pollutants.     

Gut ph and digestive strategies in estuarine grey mullet (Mugilidae) and tilapia (Cichlidae)

Tilapia guineensis , which feeds on leafy material, and Sarotherodon melanothron , which utilizes blue-green algae, were both capable of producing a pH 2 or less in the stomach which could contribute to the lysis and digestion of blue-green algae and bacteria. Of the grey mullets investigated, Liza falcipinnis had a gastric pH 3.3–4.5, which may not be low enough to cause cell lysis, whilst Liza dumerili, Mugil cephalus and Mugil curema all had stomach, caecal and intestinal pH's of 7–8.5. Grey mullet appear to have a different digestive strategy to tilapia and may rely upon the establishment of a 'colloid mill' in the stomach.     

Heterophyid metacercarial infections in brackish water fishes from Jinju-man (Bay), Kyongsangnam-do, Korea

Heterophyid metacercarial infections in brackish water fishes, i.e., perch, shad, mullet, redlip mullet, and goby, of Jinju-man (Bay), Kyongsangnam-do, Korea, were investigated using a digestion technique. Among 45 perch (Lateolabrax japonicus), the metacercariae of Heterophyopsis continua were found in 55.6% (18.5 metacercariae per fish), Stictodora spp. in 28.9% (3.6), and Metagonimus takahashii in 6.7% (17.0). The metacercariae of H. continua were detected in 23 (65.7%) of 35 shad (Konosirus punctatus). Among 15 mullet (Mugil cephalus), the metacercariae of Pygidiopsis summa were found in 100% (105.9 metacercariae per fish), Heterophyes nocens in 40.0% (8.5), H. continua in 13.3%, and Stictodora spp. in 6.7%. Among 12 redlip mullet (Chelon haematocheilus), the metacercariae of P. summa were detected in 91.7% (1,299 metacercariae per fish), H. nocens in 16.7%, and Stictodora spp. in 16.7%. Among 35 gobies (Acanthogobius flavimanus), the metacercariae of Stictodora spp. were found in 82.9% (44.5 metacercariae per fish), and H. continua in 25.7% (2.8). The adult flukes recovered from a cat experimentally infected with metacercariae from perches were compatible with M. takahashii. The results confirm that the estuarine fish in Jinju-man (Bay) are heavily infected with heterophyid metacercariae. Furthermore, it was found for the first time that the perch acts as a second intermediate host for M. takahashii.     

Escape latency is size independent in grey mullet

Using grey mullet Mugil cephalus as a model species, the hypothesis that escape latency increases with body size was tested. Minimum escape latency was c . 10 ms (mean ± s . d . 18·1 ± 13·7 ms; range 8–72 ms) and was independent of body size.     

鲻和鲮鳃丝的扫描电镜比较观察

对鲻（Mugil cephalus）和鲮（Cirrhina molitorella）的鳃丝表面结构进行了扫描电镜比较观察,结果表明,鲻鳃丝杆状部比鲮粗．鲻鳃小片高度比鲮低;两者鳃丝表面分泌孔洞口径和密度不同;鲻和鲮细胞外被不同,鲻细胞外被稀疏,鲮的则致密复杂;鳃小片细胞和鳃丝表皮细胞的表面形态存在差异,文章还描述了鳃丝表皮形态特异的细胞。     

The occurrence of fin rot in mullet (Mugil cephalus) associated with crude oil contamination of an estuarine pond-ecosystem

Four estuarine pond-ecosystems equipped with tidal simulation were established and stocked with mullet, shrimp, and oysters. A 6 month pre-spill sampling period established a consistently low incidence of disease in the mullet, Mugil cephalus , from all ponds. Following the preliminary study period, Empire Mix crude oil (4.0-5.0 p.p.m.) was spilled on each of two of the ponds in mid-July, 1974. Six to eight days following the oil spill all the mullet examined from the treated ponds had varying degrees of fin rot on one or more of their fins. The fin erosion involved primarily the caudal, pectoral, and pelvic fins with the caudal fin the most severely damaged. The degree of damage to the fins varied from a slight discoloration with no visible fraying to complete erosion of all of the fin elements. A gram negative rod tentatively identified as Vibrio sp. is considered the primary pathogen responsible for the fin erosion. Although the condition of the infected fish indicated the possibility of a systemic infection, only a low percentage of the kidney cultures taken from the diseased fish were positive indicating the infection was mostly external. The course of the infection was documented over a 56-day period following the oil spill. Significantly, 96% of the mullet observed from the treated ponds had some degree of fin damage while only 6 % of those observed from the control ponds had eroded fins. The high incidence of fin rot which occurred in the estuarine-pond ecosystems did not occur during numerous acute exposures of mullet to crude oil in the laboratory.     

A histochemical study of the lateral muscles of five teleost species

A qualitative histochemical study has been made of the myotomal muscles of five teleost fish (glass fish, Chanda ranga; carp, Carassius carassius; coalfish, Gadus virens; black mollie, Molliensia sp. and grey mullet, Mugil cephalus ) . Three or four main fibre types were distinguished in these species on the basis of the distribution and relative activities of glycogen, lipid, aglycerophosphate dehydrogenase, phosphorylase, and succinic dehydrogenase. The so-called red and white fibre types were found to have similar histochemical properties to previously investigated species. All the species studied, with the exception of the glass fish, Chanda ranga , were found to have one or two types of pink fibre situated between the red and white fibre regions. In the carp, coalfish and mullet, the pink fibres were found to be composed of small and large diameter fibres which were similar to red and white fibres respectively, except for their staining for succinic dehydrogenase. Considerable differences were found in the relative amounts of pink muscles between species. Minor fibre components were found in several species. These consisted of very small diameter fibres which did not stain well with any of the histochemical procedures used. It is suggested that these fibres represent areas of continuing muscle growth. The results obtained are discussed in relation to the division of labour between myotomal muscles during swimming.     

Pronounced genetic structure of mitochondrial DNA among populations of the circumglobally distributed grey mullet (Mugil cephalus)

Mitochondrial (ml) DNA genotypes of grey mullet ( Mugil cephalus ) from ocean basins around the world were analysed to estimate the amount of genetic differentiation in this cosmopolitan but mostly coastally-restricted species. Extensive genetic diversity was observed. Among 115 specimens from nine locales, 26 different haplotypes were detected using a battery of 13 restriction endonucleases. In phenetic analyses, these haplotypes grouped into seven distinct clusters whose members were in almost perfect accord with the geographic sources of the samples. Thus contemporary gene flow between the widespread collection locales must be absent or nearly so. Results contrast with the relative uniformity in mtDNA composition previously reported for populations of some circumglobally distributed pelagic fishes, and demonstrate that certain marine fishes with cosmopolitan distributions can exhibit pronounced population genetic structure even in the face of morphological conservatism.