Respiratory responses of the striped mullet,Mugil cephalus (L.) to hypoxic conditions*

Ventilation volume, ventilatory frequency, ventilatory stroke volume, percentage utilization of oxygen and respiratory metabolism were measured on unanaesthetized striped mullet, Mugil cephalus L., under ambient and hypoxic conditions with a modified van Dam respiration chamber. Hypoxia caused a statistically significant increase in ventilation volume, ventilatory frequency, and ventilatory stroke volume and a significant decrease in percentage utilization of oxygen. The routine rate of respiratory metabolism was not significantly altered by hypoxia. These responses probably represent ventilatory adjustments which serve to maintain a constant oxygen supply to the gills under conditions of oxygen depletion.     

Effect of rearing density on the blood and tissues of mullet (Mugil cephalus L.)

This study evaluated the biological effects of high stocking density on mullet (Mugil cephalus). Fifty fish, caught from Faro lake, were divided into two groups, a low-density control group (n = 15), stocked at 3.4 kg/m³ in an 800 l tank and a high-density experimental group (n = 35), stocked at 8.4 kg/m³ an 800 l tank. The ammonia concentration in the control group tank reached 0.3 mg/l after 2 days while that in the experimental tank reached 5 mg/l. Haematological parameters and serum protein profiles were determined following blood sampling. An Unpaired T-test showed significant differences between the two groups on Red Blood Cell Count, Haematocrit, Haemoglobin, White Blood Cell Count, Mean Corpuscular Haemoglobin, Mean Corpuscular Haemoglobin Concentration, total proteins, albumin and α-globulins. In the experimental group, the disappearance of prealbumin and the γ-globulin fraction was particularly evident. Histopathological changes indicated that mucosal electrolytic failure was the main function compromised. This could eventually lead to death. The findings suggest that mullet is sensitive to stocking density linked to ammonia toxicosis.     

Studies on bacterioplankton and inhibitory strains of aquatic actinomycetes in Lake Bardawil,Egypt

Lake Bardawil represents a hyper-saline shallow (50–600 cm deep) water basin lying along the northern shore of Sinai. Surface water samples were collected monthly from this lake for physico-chemical and microbiological analysis. Seasonal variations in the averages of temperature, pH and transparency of the tested water samples were determined. Seasonal averages of the total bacterial counts at 22 and 37°C, biovolumes of cells and bacterial biomass of the lake’s water at different regions were also determined. In addition to the gram-negative pathogen, Edwardsiella tarda, faecal contamination indicators, total coliforms, faecal coliforms and faecal streptococci were counted in the lake’s water samples from various regions during different seasons. The number of actinomycetes per milliliter of the lake’s water samples were determined. Fifteen actinomycetes were isolated and screened for their antibacterial activity against E. coli and pathogenic E. tarda isolated from the same water samples. Five isolates of these actinomycetes showed antibacterial activities and nine of them were identified as Streptomyces. The most antibacterially active isolate was subjected to morphological, physiological and biochemical studies and identified as Streptomyces viridiviolaceus. The identified organism exhibited antimicrobial activities against the main indicator of water pollution, E. coli, pathogenic E. tarda, Corynebacterium michiganese B-33, Pseudomonas solanacearum B-3212 and Staphylococcus. No antimicrobial activities were recorded against Bacillus cereus, Micrococcus, Mycobacterium, Aspergillus niger, Candida albicans, C. tropicalis or Rhizopus nigricans.     

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.     

Influence of some environmental variables on the ascorbic acid status of mullet, Mugil cephalus L., tissues

The seasonal fluctuations in the ascorbic acid (AsA) and ascorbic acid 2-sulphate (AsA 2-sulphate) content of mullet, Mugil cephalus , tissues were examined. Ascorbic acid concentrations in brain, gill and hepatic tissues showed seasonal changes, but the pattern of AsA fluctuations in each tissue differed. The AsA content of mullet brains decreased during the summer, whereas hepatic AsA concentrations increased during this period and were maximal by the end of June. Hepatic AsA reserves declined after environmental water temperatures dropped below 18°C and reached a minimum (20 μg g⁻¹) by the end of January. Greatest fluctuations in AsA content occurred in gill tissues, which had a four-fold range of tissue concentrations. There were also seasonal changes in the AsA 2-sulphate content of brain and hepatic tissues. These differences among mullet tissues in the seasonal patterns of AsA content may be due to diverse effects of environmental variables on tissue AsA reserves. The ability of hepatic and renal tissues of mullet and several other teleost species to synthesize AsA was also investigated. L-gulonolactone oxidase activity was detected in all the species examined, but in all cases the biosynthetic capacity was less than a seventh that in goldfish, Carassius auratus , livers. Mullet appear to have only a limited capacity to synthesize AsA.     

Validation of an in vivo method for monitoring ovarian development in the grey mullet (Mugil cephalus L.)

The validity of using extruded intra-ovarian oocytes for in vivo assessment of ovarian maturity in the grey mullet was established. The diameter of sampled, unfixed oocytes was used as a reference point for comparative purposes. Analysis of variations in oocyte diameters among samples removed from seven different ovarian locations indicated that mullet oocytes develop in synchrony and that in vivo samples taken from any area in the ovary would be representative of the entire ovary. Statistical analyses of oocyte diameters and diameter-frequency distributions data from duplicate in vivo samples removed from the same ovarian site in each of 17 females showed no significant differences and validated the accuracy of the method. Similar comparisons of data from in vivo and in vitro samples revealed no statistically significant differences.     

Ontogenesis of osmotic regulation in the striped mullet, Mugil cephalus L.

The osmoregulatory capabilities of juvenile striped mullet, Mugil cephalus L ., of three size-groups (20–29, 30–39 and 40–9 mm s.l.) were compared in a series of six salinities ranging from fresh water to full sea water. The two smaller size-groups were able to tolerate instantaneous transfer from the brackish water in which captured, to all salinities but fresh water, while the 40–69 mm group were tolerant of instantaneous transfer to all experimental salinities. At high environmental salinities, the osmotic regulatory capabilities improved with growth in size to an apparently definitive condition in fish of 40–69 mm s.l. The smallest of these individuals were estimated to be about 7.5 months old. The osmotic regulatory capability in waters of low salinity had reached a definitive state with the development of tolerance to such salinities. The ontogenetic pattern for Mugil cephalus is virtually identical to that of the Atlantic salmon, Salmo salar .     

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.     

Thermal response of juvenile Hawaiian mullet Mugil cephalus (L.) to acclimation time and fluctuating low temperatures*

Rates of acclimation and the response to fluctuating low temperatures of juvenile striped mullet Mugil cephalus (L.) have been described in terms of changes in heat resistance over a period of time. Fish changed from 25.5 to 27 or 29° C were acclimated within seven days. Acclimation to 23 or 15° C required a maximum of 11 days. Thermal responses to fluctuating low temperatures were lower than responses to constant temperature levels. Cyclic variations in heat resistance were present in all experimental and control tests.     

Histology of the pituitary gland of the grey mullet, Mugil cephalus L.

The present communication deals with a histological study of the pituitary gland of the teleost fish Mugil cephalus , found in the estuarine waters of Cochin area. Six different cell types were identified in the pituitary gland on the basis of their grouping, distribution and staining properties. The prolactin and the TSH cells (thyroid stimulating hormone producing cells or thyrotrops) were identified in the rostral pars distalis and the ACTH cells (adrenocorticotropic hormone producing cells or corticotrops) in the interphase between the neurohypophysis and the rostral pars distalis. The STH cells (somatotropic hormone producing cells or somatotrops) and the gonadotropic cells were distinguished in the proximal pars distalis and the MSH cells (melanin stimulating hormone producing cells or melanotrops) in the pars intermedia.     

The feeding periodicity of striped mullet, Mugil cephalus L., in two Florida habitats

The feeding periodicity of Mugil cephalus (striped mullet) was investigated during the summer and autumn of 1979 using percentage body weight made up of stomach contents as an indicator of feeding intensity. One study site was freshwater, the other was estuarine and both were tidally influenced. Mullet at both sites feed diurnally, with maximum intensity occurring at about 11.00 hours and little or no feeding occurring at night. Fish from the freshwater site have larger standard length-specific intestine lengths and also include more plant material in their diet than do mullet from the estuarine site. At both sites fish longer than 28 cm standard length ( s.l. ) tend to be female; the difference from a 50:50 sex ratio is highly significant in both cases. Females longer than 28 cm s.l. outnumber all other sex and size combinations at the freshwater site, but comprise only 28% of fish collected at the estuarine site.     

Population biology of parasites of striped mullet, Mugil cephalus L. I. Monogenea

Young-of-the-year (class 0) and yearling (class 1) striped mullet, Mugil cephalus , were collected from Sapelo Island, Georgia from May 1970 to June 1971 to study the development, seasonal abundance and relationship of environmental variables to parasitic populations. The number of species of parasites increased with age of the host. Initial infection appeared to be influenced by closeness of association of mullet age classes, by the period of abundance of a parasite on class I mullet and by the mobility of the infective parasitic stage. Fluctuations in intensity and prevalence of a parasite on class 0 mullet were similar to those of class I mullet after the initial infection. Ancyrocephalus vanbenedenii was first observed on class 0 mullet in March. Intensity was high on both classes in spring and on reproductively active mullet in late autumn. Prevalence on both classes was above 80% except in late summer. Polyclithrum mugilis was not observed on class 0 mullet until August even though intensity and prevalence on class I mullet was highest during early spring. Gyrodactylus mugelus did not occur on class 0 mullet but appeared on class I mullet during late summer. Microcotyle psuedomugilis was observed on class 0 mullet in early summer and Metamicrocolyla maeracantha in October. Both species occurred but at a low intensity on class I mullet.     

Motility of Mugil cephalus L. spermatozoa in coelomic fluid, seminal fluid and saline media

The aim of this study was to assess the motility duration of Mugil cephalus when exposed to seminal fluid, coelomic fluid and saline media. Hypo-osmotic activation medium (distilled water containing bovine serum albumin 10 or 30 mg ml⁻¹) did not trigger sperm motility. Saline solution containing 500 m m NaCl, 3.1 m m KCl, 0.2 m m Tris, 3.4 m m CaCl₂, pH 7.5 initiated the sperm activation and the motility lasted for more than 2 min. Coelomic fluid showed an inhibitory effect for triggering the motility of spermatozoa. Higher salinity increases the motility duration of sperm. The optimum motility duration was shown in salinity 32 psu.     

Cucculanus bioccai n. sp. (nematoda: cucullanidae), parasite of Mugil cephalus L

Cucullanus bioccai n. sp. described from the intestine of Mugil cephalus caught in Lake Sabaudia (Latina, Italy) is compared with C. dodsworthi and C. mugili parasites of mullets. It differs from C. dodsworthi mainly for the position of the 1st pair of precloacal papillae, the position of vulva, the shape of gubernaculum, the measurements of eggs; from C. mugili for the number of papillae, the position of the 1st pair of precloacal papillae, the conformation of cloaca and the position of vulva.     

Influences of Ca and Mg ions on the egg survival of grey mullet, Mugil cephalus L.

Five kinds of artificial sea water with similar salinity, pH and osmolarity were prepared with different concentrations of calcium and magnesium ions. They were complete sea water, calcium-free sea water, half calcium-free sea water, magnesium-free sea water and half magnesium-free sea water. The fertilized eggs from induced spawnings of grey mullet Mugil cephalus , were transferred to these sea waters at two development stages, i.e. before the formation of 2-blastomere stage and at the gastrula stage. Survivals of fertilized egg in different sea waters were checked after several hours incubation, the percentage survival was used as an index of the importance of calcium and magnesium to the embryonic development. The results showed that calcium is indispensable to the embryonic development of mullet egg. Magnesium, however, is not the necessary element in the incubation medium.     

Ultrastructural study of the esophagus of seawater-and freshwater-acclimated Mugil cephalus (Perciformes,Mugilidae), euryhaline marine fish

The esophagus of the common grey mullet Mugil cephalus shows a single mode of organization that is common to both seawater- and freshwater-acclimated specimens. A short anterior segment is lined by a stratified epithelium with mucous cells; posteriorly, this is progressively replaced by single-layered columnar epithelium. Ultrastructural features of the columnar epithelium are quite similar in the seawater- and freshwater-acclimated specimens. Apical microvillous projections, lamellar structures, and dilated intercellular spaces are observed. The present study suggests that the mullet esophagus is involved in active ion transport and water permeability, both in seawater and in freshwater environments. © 1993 Wiley-Liss, Inc.     

Predation by Nile perch Lates niloticus (L.) on Oreochromis niloticus (L.), Cyprinus carpio (L.), Mugil sp. and its role in controlling tilapia recruitment in Egypt

Vulnerability of three fish groups (tilapia, common carp, mullet) to predation by Nile perch Lates niloticus was evaluated. The study was conducted in aquaria and in cages placed in concrete ponds. Common carp Cyprinus curpio was the more vulnerable to predation by Nile perch followed in order by mullet ( Mugil cephulus and M. cupito ) and Nile tilapia Oreochromis niloricus . Medium-size Nile perch (30–32 cm t.l. ) were able to consume tilapia up to 14 cm t.l. , while tilapia of 15 cm total length were not eaten. Ratios of 1 : 10 to 1 : 15 between Nile perch and ready-to-spawn females of O. niloticus were found to be adequate to control tilapia reproduction.     

Water and ion balance in hydrating oocytes of the grey mullet, Mugil cephalus (L.), during hormone-induced final maturation

Sequential changes in water content and inorganic ion concentrations occurring in intra-ovarian oocytes of the grey mullet, Mugil cephalus L., during hormone-induced final maturation are described. Post-vitellogenic oocytes have a water content of 59.4%. During final maturation, oocyte water increases rapidly to a maximum of 84.8% at oviposition. Hydration is accompanied by a relatively small increase in dry matter due to the concurrent uptake of inorganic ions and an apparent uptake of organic matter. Net uptake of Ca²⁺ during hydration is negligible. Net uptake of Mg^{2 +} and Na⁺ occurs in less than equimolar proportions. Net uptake of K⁺ and Cl^? occurs in greater than equimolar proportions prior to ovulation, returning to equimolarity at oviposition. Hence, hydration results in a dilution of intracellular Ca²⁺, Mg²⁺ and Na⁺ to minimum concentrations at oviposition. In contrast, K⁺ and Cl^? concentrations are slightly elevated prior to ovulation, returning to initial levels at oviposition. A 1:1 stoichiometric relationship in net uptake of K ⁺ andCl^? is evident. Intracellular osmotic pressure in post-vitellogenic oocytes is 203.4 ± 18.0 mOsmolkg^?1. Osmotic pressure rises to a peak of 421.3+ 17.3 mOsmol kg^?1 prior to ovulation, then declines to 313.3 ± 15.0 mOsmol kg^?1 at oviposition. This rise in osmotic pressure prior to ovulation cannot be accounted for solely on the basis of inorganic ion uptake and must be attributed to changes in intracellular concentrations of organic solutes as well. An apparent increase in non-ash dry matter during hydration suggests that a net uptake of organic solute is involved. A relatively small organic molecule with high osmotic activity (e.g., amino acids) is implicated.