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 .     

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.     

Ontogenetic dietary shifts and morphological correlates in striped mullet,Mugil cephalus

Synopsis Ontogenetic dietary shifts are well studied in fishes. However, these shifts are rarely correlated with habitat and morphology. This study investigates: (1) ontogenetic dietary changes in mullet; and if dietary shifts do occur (2) whether they are correlated with feeding location, feeding behavior and/or feeding morphology. Stomach contents from eight size classes, each with 25 individuals, were analyzed using a gravimetric sieve fractionation procedure, Czechanowski's Quantitative Index and cluster analysis. Core samples (5 mm deep) were also analyzed in the same manner. Morphological characters were measured to detect differences among the size classes. Cluster analysis showed three distinct trophic units for Mugil cephalus in Cross Bayou: (1) 20.0 mm standard length — 30.0 mm SL; (2) 30.0 mm SL — 40.0 mm SL; and (3) 40.0 mm SL — > 100 mm SL. Comparison of the gut contents to the sediment contents for each size class showed an increase in similarity as the fish grew. Mullet gut contents from fish 20–25 mm SL were only 45% similar based on the weights of the prey items to the sediment subsample prey items, while stomach contents from fish > 100 mm SL were 84% similar to the sediment subsample contents. Gill raker length and interraker spacing of four gill arches were allometric with respect to standard length. Prey particle size within size classes appeared to be more correlated with feeding behavior than gill interraker spacing because smaller particles than predicted by the interraker spacing were ingested. It is suggested that smaller fish may be browsing more selectively than larger fish which graze.     

Motile aeromonas infection of striped (grey) mullet Mugil cephalus

Infection of striped mullet (Mugil cephalus) with Aeromonas hydrophila results in an acute septicemic disease. The disease can be experimentally induced by intramuscular injection, skin or gill scarification or by the oral route using pellets purposely seeded with bacteria. The organism was isolated from the blood 1–2 days after infection and from all organs 24 hr or longer after infection. The disease is characterized by early inflammatory and proliferative changes and later necrotic changes. Enteritis and hepatic necrosis are constant findings in aeromonad disease of M. cephalus but surface lesions are not pathognomic for these infections in mullet. Death of infected fish may be attributed to bacterial toxins which cause necrosis of parenchymal organs and soft tissue structure.     

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.     

Salinity and oxygen tolerances of eggs and larvae of Hawaiian striped mullet,Mugil cephalus L.*

Salinity and oxygen tolerances of eggs and larvae of Hawaiian striped mullet (Mugil cephalus L.) were studied. Optimal salinities for eggs incubated at 19.5-20.5°C were 30–32‰. Maximum larval survival occurred within the salinity range of 26–28‰. Significant decreases in egg survival occurred with eggs incubated in mean oxygen concentrations below 5.0 p.p.m. and for larvae held in mean oxygen concentrations below 5.4 p.p.m. The results are discussed in terms of spawning sites and the effects of oxygen saturation values on fish eggs and larvae.     

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.     

Ascorbic acid status of mullet, Mugil cephalus Linn., exposed to cadmium

The effects of acute and chronic cadmium exposures on ascorbic acid concentrations and cadmium accumulation in the tissues of juvenile mullet, Mugil cephalus , are described. Hepatic ascorbic acid reserves were maintained in untreated mullet fed a diet containing ascorbate, but decreased 60% in individuals exposed to 10 mg Cd 1^-1 for six weeks. Ascorbic acid depletion was accompanied by a massive accumulation of cadmium in the liver. Similar changes were found in gill tissue. In contrast, ascorbic acid concentrations were largely unaffected in kidney tissue which had a limited capacity to accumulate the metal. There were marked fluctuations of ascorbic acid levels in the brain. Only small amounts of cadmium were accumulated by this tissue. These results indicate that in mullet liver, gill and brain ascorbic acid stores may be depleted during chronic cadmium poisoning.     

Induced spawning of the striped mullet Mugil cephatus L.

The response of adult mullet to artificial hypophysalion, immediately before the onset of the spawning migration was studied. Both males and females received intraperitoneal injec-tions of mullet or salmon pituitary homogenates wth ACTH or Synahorin (APE+HCG) three times per week for 12 days. At the outset, conlrol females were in the tertiary yolkstage with a low mean GSI of 7.6, while males gave thick, non-dispersing milt. Two of fourfemales receiving one salmon pituitary plus 25 RU Synahorin per injection spawnedspontaneously in laboratory aquaria. Released eggs were buoyant, well formed and had a mean diameter of 570μm. Egg fertility could not be ascertained due to protracted contact with sea water. Spawned females extruded a meinbranous tissue 'plug' from the cloaca1 region which was subsequently retracted. The remaining experimental females were refractory to treatment and histological examination of the ovaries revealed a predominance of atretic oocytes. All males were refractory to treatment and milt hydration was not achieved. It is suggested that induction of early spawning is possible especially with higher doses of pituitary homogenates and Synahorin. [Oceanic lnstitute Contribution No, 62 Sea Grant Program, GH-76].     

A GM2-specific beta-hexosaminidase from the roe of striped mullet (Mugil cephalus)

The roe of striped mullet (Mugil cephalus) was found to contain a beta-hexosaminidase different from the beta-hexosaminidases isolated from other sources. The enzyme from mullet roe is able to cleave GalNAc from GM2 without the assistance of either an activator protein or a detergent. It also cleaves the oligosaccharide derived from GM2 and other oligosaccharides containing the GM2 sequence GalNAc beta 4(NeuAc alpha 3)Gal-. However, it is not effective in hydrolyzing neutral glycosphingolipids containing terminal GalNAc or GlcNAc, such as GbOse4Cer, GgOse3Cer, or LcOse3Cer. These results indicate that mullet roe beta-hexosaminidase can specifically cleave GalNAc from the glycoconjugates containing the GM2 sequence. No beta-hexosaminidase with such specificity has been previously described. Thus, this unique enzyme should be very useful for the detection and analysis of glycoconjugates containing the oligosaccharide chains with GM2 sequence.     

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.     

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.     

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.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Induced spawning of grey mullet Mugil cephalus L. with fractionated salmon pituitary extract

The efficacy of fractionated salmon pituitary gonadotropin as a spawning agent in Mugil cephalus L. was tested. Natural spawning was induced in all females with a total dose of 11.9–20.9 μg/g body wt. Spawning dose varied inversely with initial mean egg diameters of recipient females. A 'critical' mean egg diameter of 650–700 μ was observed to precede the hormone dose that induced spawning. A 'priming' effect was observed following the initial injection and is discussed. The 'latency period' was determined to be 10–15 h; fecundity was estimated at 648 eggs/g body wt. Courtship, spawning and fertilization occurred naturally with uninjected males.     

Influence of some environmental variables on the ascorbic acid status of striped mullet, Mugil cephalus Linn., tissues. III. Effects of exposure to oil

Exposure to water-soluble fractions (WSF) of a crude and two fuel oils altered the ascorbic acid (AsA) content of several striped mullet, Mugil cephalus , tissues. Exposure to sublethal concentrations of all three WSFs caused a depletion of AsA reserves in brain, gill, kidney and liver tissues, but not in muscle. There was a marked decline in AsA stores in kidney and gill tissues after only one day of exposure to WSFs of both crude and fuel oils. Liver AsA concentrations were significantly depleted after one week of oil exposure. Brain AsA content was only significantly depleted during chronic exposure to the highest oil concentration (20% WSF). A dose-dependent depletion of AsA reserves in the liver but not in the other tissues was observed one week after a single exposure to 2–20% WSFs of a No. 2 fuel oil. Exposure to 20% WSF of the No. 2 fuel oil caused a 47% decrease in liver AsA content one week later. Hepatic concentrations were still significantly depleted after 15 days, but had returned to control levels 20 days after the initial exposure. The data suggest that the depletion of tissue AsA reserves in fish inhabiting oil-contaminated environments could be sufficient on occasions to lead to AsA deficiency.