Maturity and fecundity of golden grey mullet (Liza aurata Risso, 1810) in Iranian waters of the Caspian Sea

The objective of the study was to determine some reproductive parameters in the golden grey mullet (Liza aurata Risso, 1810) during two periods half a decade apart while also trying from limited data to identify changes in fecundity over the past half century. Maturity and fecundity of golden grey mullet caught in Iranian waters of the Caspian Sea is not well documented and were thus studied during several seasonal cycles during 2002–2004 to establish basic data on reproduction in the area. The fork length (FL) of 462 sampled fish was between 22.1 and 51.9 cm. The fork length–weight relationship derived from all fish was W = 0.0118FL^2.964. Overall male to female ratio was 1 : 1.42. The reproductive season extended from October to December. Fifty percent of sexual maturity was at FL 26.0 cm. Mature gonads were present in 20% of fish at age 3, 63% at age 4, 88% at age 5, and 97% at age 6. Individual absolute fecundity of the golden grey mullet ranged from 113 386 to 1.47 million eggs, with a mean (±SD) of 451 963 (±274,114.2). An overlap exists between the spawning and fishing seasons. Therefore, the start of the fishing season should be delayed for 1 month in order for stocks to complete their spawning.     

Ultrastructure of spermiogenesis in Liza aurata Risso, 1810 (Teleostei,Mugilidae)

Summary Sequential cytological events in late spermatogenesis of Liza aurata were studied from the stage secondary spermatocytes to that of mature spermatozoa. Spermiogenesis involves preparatory morphological events followed by conspicuous modifications such as intracellular movements (diplosome and mitochondrion migration, spermatid lengthening, nuclear rotation) and structural changes (dense chromatin granules, increase in size of mitochondria, loss of cytoplasm). Mature spermatozoa, with a round nucleus and a pseudo-midpiece are of a primitive type, even compared with spermatozoa of other teleosts.     

Hemoglobin system of golden mullet (Liza aurata,Risso) at adaptation to conditions of outer hypoxia

Under conditions of experiment, effect of outer hypoxia on the hemoglobin heterogeneous system and respiratory blood characteristics were studied in the golden mullet Lisa aurata R. The control fish group was maintained at oxygen pressure of 158–162 gPa, the experimental group at 54–55 gPa. The exposure was 15 days, the water temperature—15°C. Under conditions of oxygen deficit in the mullet body there is noted development of a complex of compensatory reactions directed to maintenance of the oxygen blood capacity. Initially (the 1st–2nd day), the release of erythrocytes from spleen is noted, which increases the number of red blood cells and the hemoglobin concentration in blood (the emergency adaptation). Subsequently (the 10–15th day), there occur quantitative readjustments at the level of the hemoglobin system, which lead to an increase in the blood affinity to oxygen and to a decrease in its sensitivity to pH (the long-term adaptation). The revealed changes take place on the background of a decrease in volume of circulating erythrocytes, which reflects the character of change of erythrocytic parameters (MCV, MCHC) and seems to be a consequence of partial dehydration of blood plasma.     

Fine structure of hepatocytes in juvenile grey mullets: Liza saliens Risso, L. ramada Risso and L. aurata Risso (Teleostei, Mugilidae)

Livers of 45 fingerling grey mullets ( Liza sp. 5-15 cm long) were subjected to light microscopy, transmission electron microscopy and enzyme cytochemical examination. The hepatic structure was found to be comparable in all three Liza species. As in other fish species, Liza liver parenchyma is arranged in cords (or dual-plated laminae, in sections parallel to the sinusoidal axis). Hepatocytes showed numerous microvilli in their perisinusoidal and canalicular areas. They contained a centrally located nucleus, fairly large areas of rough endoplasmic reticulum, consisting mainly of parallel cisternae, and pools of glycogen. A few small lipid droplets were evenly distributed in the cytoplasm. The Golgi fields, between the canaliculus and the nucleus, consist mainly of dictyosomes, lysosomes and autophagic vacuoles. Acid phosphatase activity was cytochemically localized to reaction products in secondary lysosomes and lipofuscin granules. A comparison between grey mullet liver and that of other teleosts was made.     

Studies on the small grey mullet Liza malinoptera (Valenciennes)

The growth of Liza malinoptera , which is analysed by its morphometric and length–weight relationships, is found to follow closely the so-called cubic law for isometric growth. The relative condition factor Kn is used to investigate the condition cycle and for maturity studies. Fecundity and ova size are estimated. The fish is a herbivorous iliophage utilising mainly mangrove plant detritus at the first trophic level. Fine particle selection is demonstrated during feeding. Studies on the morphology and histology of its alimentary tract indicate an adaptive correlation with its food and feeding habits.     

Reproduction in the greenback grey mullet, Liza subviridis (Valenciennes, 1836)

This paper presents data on the reproductive biology of Liza subviridis , a little studied mullet species. The fish is heterosexual, exhibiting external fertilization. Six maturity stages can be macroscopically identified in the testes and seven in the ovaries. The macroscopic changes in the gonads are manifestations of histological changes occurring in the development of sperm cells and oocytes. First sexual maturity is attained in the length ranges of 9.5–11.5 cm and 10.5–11.5 cm in male and female fish respectively. The fecundity for fish measuring 10.3–13.9 cm in standard length ranged from 40 000–145 000 eggs. The relationship between fecundity ( F ) and length ( L ) can be represented as: F = 1.9044 L ^4.2998. The spawning duration in L. subviridis is restricted to a short and definite period, with all ripe ova being released within a single spawning act. A pronounced spawning season can be detected to extend from June to November. However, during off-seasons, some spawning also occurs. The correlations between spawning, rainfall and air temperature is discussed.     

Pinealectomy and ovarian development in the grey mullet, Liza ramada

Adult female specimens of Liza ramada were pinealectomized and sham-pinealectomized, and the development of their ovaries was followed over a period of 14 weeks and compared with those of untreated controls. Pinealectomized specimens exposed to long photoperiod (16L/8D) for 14 weeks, showed undeveloped ovaries, with a maximum oocyte diameter of less than 100 μm, and a gonadosomatic index of 0·6 similar to that of sham-pinealectomized and control specimens. In pinealectomized females exposed to short photoperiod (8L/16D) for 6 weeks, the mean diameter of oocytes was 270 μm v . 155 μm in control and sham-pinealectomized specimens. After 9 weeks, the oocytes in pinealectomized specimens reached 430 μm as against 265 μm in the controls. Within 14 weeks of pinealectomy, mean oocyte diameter was 480 um while it was 400 μm in controls and sham-pinealectomized specimens. It is tentatively concluded that the pineal complex has an inhibitory effect on ovarian function in Liza ramada exposed to short photoperiod.     

Fine structure of early previtellogenic oocytes in Mugil (Liza) auratus Risso, 1810 (Teleostei,Mugilidae)

Summary Sequential cytological events at the onset of previtellogenesis were studied in oocytes from 12 m to 70 m in diameter of golden grey mullet. The main cytological changes observed (increase in size of cell, nucleus, nucleolus and increase in number of nucleoli, RNP particles, nuage and mitochondria) provide evidence for important synthetic processes in an early preparatory phase of oocyte development.Somatic cells (pre-follicle, follicle and thecal) are also described.     

Age and growth of the sand smelt, Atherina boyeri (Risso 1810), in the Mar Menor coastal lagoon (SE Iberian Peninsula)

The age and growth of sand smelt, Atherina boyeri (Risso 1810), in the Mar Menor (SE Iberian Peninsula) were studied in samples taken from catches of local fishermen obtained between November 1997 and September 1998. The maximum lengths were 94 mm (FL, fork length) in females and 87 mm (FL) in males. Age determination based on scale readings and validated by length frequency analysis shows that the population has a 3‐year life cycle. Females were significantly longer than males in each of the age classes. Both sexes of the sand smelt grow allometrically (b = 3.113 males; b = 3.043 females) and attain approximately 56.2% of their maximum fork length in their immature first year, after which the annual growth rate drops quickly. The highest growth rate was observed from winter to spring (G_L = 16.01 males 1+; G_L = 11.25 males 2+; G_L = 17.18 females 1+; G_L = 9.62 females 2+). The condition cycles were similar for both sexes, with a minimum in June–July and two maximums in April and November.     

梭鱼消化系统的组织学研究

采用石蜡切片等组织学研究手段,以生活于海水和咸淡水中的梭鱼Liza haematocheila作为实验材料,对其消化系统的组织学结构进行了观察.比较了消化道各部分粘膜褶皱的高低、多少、疏密程度,粘膜上皮细胞的类型,杯状细胞在数量上的变化以及消化道肌层的肌肉组织类型和肌细胞的排列方式.结果显示:咸淡水梭鱼的肠道中杯状细胞的数量多于海水梭鱼,食道是横纹肌,但其它消化道均为平滑肌.肝脏中肝小叶不明显,肝细胞索明显.胰腺呈弥散状分布,其中有胰岛存在.     

Feeding habits of sand smelt (Atherina boyeri, Risso 1810) in Trichonis Lake (Western Greece)

The feeding habits of sand smelt (Atherina boyeri, Risso, 1810) from Trichonis Lake (Western Greece) were investigated. Stomach contents were analyzed from 240 specimens with total lengths ranging from 35 to 112 mm. Samples were taken at monthly intervals (January–December 1997). Of the total number of stomachs examined, 53 were empty (22.1%). However, values varied greatly with season (maximum in January: 50%; minimum in August: 7.6%). Prey analyses of stomach contents identified 15 important items (%Rn > 0.05) belonging to six major groups: crustacean (copepods, cladocera), mollusca (bivalve: larvae), insects (larvae), cestode worms and finfish (fry and eggs). Dominant prey were larvae of the bivalve Dreissena polymorpha (%Rn = 33.8), the copepods Eudiadomus drieschi (%Rn = 26.4) and the cladocera Diaphanosoma brachyurum (%Rn = 24.2). The importance of cladocera and copepods decreased with increasing size of the sand smelt, while the importance of bivalve larvae, fish eggs and finfish fry increased with increasing sand smelt size. Seasonal changes in diet composition and prey abundance in sand smelt stomachs were recorded as coinciding with the seasonal composition and abundance of the zooplankton community in the surface layers of Trichonis Lake. Bivalve larvae were the dominant prey of A. boyeri during January to May, while copepods and cladocera dominated from June to December.     

Ecology and exploitation pattern of a landlocked population of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece)

Age, growth, mortality and exploitation pattern of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece) were studied from samples taken from catches of local fishermen. Individuals ranged between 44 and 109.53 mm in total length (TL). Age determinations based on scale readings show that the population has a 4-year life cycle. Sand smelt grows allometrically (b=3.18) and relatively rapidly, achieving 52.3% of the growth during the first year; thereafter the annual growth rate drops quickly. The von Bertalanffy growth parameters for all individuals are: L_∞=112.40 mm, k= 0.42 years⁻¹και t_o=−0.40 years. The total mortality rate was Z=1.65 years⁻¹ and the natural mortality rate M=1.07 years⁻¹. The exploitation rate indicates that the population is rather underexploited (E=0.35).     

The immune response of the thick-lipped grey mullet, Chelon labrosus (Risso, 1826), to metacercarial infections of Cryptocotyle lingua (Creplin, 1825)

Grey mullet, Chelon labrosus , (60–100 g) have been found to respond immunologically to Cryptocotyle lingua , following a single exposure to 20000 cercariae, by the production of humoral antibody, sensitized pronephric leucocytes and cytotoxic serum factors. Antibody titres measured by passive haemagglutination reached a peak at week 4 with a -log₂ titre of 16±S.E. 1.0, and titres of 10.7±S.E. 1.0 were still recorded after 10 weeks at the termination of the experiment. Cercarial agglutination was found unreliable as a rapid test. Pronephric leucocytes, sensitive to cercarial antigen when measured by the under-agarose migration method, were detected between weeks 1 and 6, peaking at week 2. In vitro polarization was increased when cells were incubated with the antigen, but this increase was not significantly different between control and infected fish. Heat-labile cytotoxic factors of immune sera have been demonstrated to whole cercariae in vitro , these factors being associated with structural damage to the tegument. Pronephros cells isolated from immune fish during each week of infection showed no evidence of adherence to cercariae or metacercariae in vitro. The results are discussed in relation to both host response and course of infection of the parasite.     

Age, growth and mortality of a semi-isolated lagoon population of sand smelt, Atherina boyeri (Risso, 1810) (Pisces: Atherinidae) in an estuarine system of northern Greece

Age, growth and mortality of the sand smelt, Atherina boyeri (Risso, 1810), were studied in the Vistonis estuarine system in northern Greece from February 1989 to August 1990. Overall male : female sex ratio was 1 : 2.5, statistically different from unity. Total lengths ranged between 13 and 105 mm. Age determination based on scale readings showed that the population comprised five age‐groups. Sand smelt grew allometrically (b = 3.22) and rapidly during the first year, achieving 60% of their growth. Growth parameters of the population were: L_∞ = 116.97 mm, K = 0.35 year⁻¹ and t_o = −0.99 years. Growth index ϕ′ was 3.69 of all individuals studied. The mean growth index was significantly lower for the Mediterranean lagoon (ϕ′ = 3.73, SD = 0.1) than for Atlantic populations (ϕ′ = 3.92, SD = 0.06). Total mortality rate was Z = 1.29 year⁻¹ and natural mortality M = 0.95 year⁻¹. Males had a lower life span than females, the latter dominating length classes >60 mm. Exploitation rate of the studied population was E = 0.26, suggesting that stock size might increase and generate improved possibilities for exploitation.     

Effects of leaping grey mullet Liza saliens (Osteichthyes, Mugilidae) in the macrophyte beds of oligohaline Mediterranean coastal lagoons

Some mugilid fish are known to enhance small phytoplankton in freshwater macrophyte-free environments due to zooplankton depletion. This suggests that they may have negative effects on natural macrophyte beds of freshwater and oligohaline lagoons due to phytoplantkon enhancement. To test this hypothesis, we compared the ecosystems of control enclosures that contained no fish with those of enclosures stocked with Liza saliens at two different densities. The occurrence of L. saliens at a density of 321±92.42 kg ha^–1 reduced cladoceran density, depleted epiphytic chironomid larvae, enhanced mayfly nymphs and cyclopoid copepods and reduced the organic matter content of sediment, all in comparison with control enclosures. At a density of 673±42.04 kg ha^–1, L. saliens reduced total zooplankton density, depleted epiphytic and sediment dwelling chironomid larvae and enhanced mayfly nymphs. The organic matter contents of sediment was not affected. These results showed that L. saliens was very effective in reducing zooplankton density even when macrophyte biomass was high. However, these effects do not affect phytoplankton density, probably because zooplankton was dominated by species with low filter-feeding rates and macrophytes depleted nutrients.     

Age and growth of the hollowsnout grenadier, Caelorinchus caelorhincus (Risso, 1810), in the Aegean Sea

Age and growth of the hollowsnout grenadier was studied based on samples collected seasonally in the Agean Sea between March 2003 and January 2004. Total length ranged from 9.0 to 21.6 cm. Length–weight relationship was described as a = 0.0032, and b = 3.008. Age determinations based on otolith readings were between 1 and 10 years. The von Bertalanffy growth curve fitted to observed lengths‐at‐age provided parameters of L_∞ = 24.9 cm, k = 0.115 and t_o = ?3.494.     

Effect of hypoxia on the content and stoichiometry of cytochromes in muscle of the gray mullet Liza aurata

The maintenance of the gray mullet Liza aurata under conditions of hypoxia ( $ P_{O_2 } The maintenance of the gray mullet Liza aurata under conditions of hypoxia ( 55–82 GPa) for 1–2 days led to a decrease of oxygen tension in arterial blood by 47%, while in venous blood—by 28%. The mean muscle oxygen tension decreased by 19.2%. The number of hypoxic and anoxic zones in muscle tissue decreased significantly, in particular in red muscle. The maintenance of the fish in hypoxic waters for 15 days led to a rise of the content of cytochromes in muscle and a qualitative readjustment of the mitochondrial respiratory chain manifested in an increase of the content of cytochromes a and a3 and a decrease of cytochrome b. In discussion, literature data are presented which support the described regularity. Original Russian Text ? A. A. Soldatov, M. V. Savina, 2008, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2008, Vol. 44, No. 5, pp. 508–512.     

The food and feeding habits of greenback grey mullet, Liza subviridis (Valenciennes), from different habitats and at various stages of growth

An analysis of the stomach contents of Liza subviridis at various stages of growth and from different habitat types is given. Transitions in diet with respect to size were observed. Postlarval stages of less than 12 mm standard length fed only on zooplankton. The transition to bottom feeding occurred in specimens 16–20 mm, with food items consisting of zooplankton, diatoms, detrital material and inorganic sediment. The transition was complete on attaining a length of 24 mm whereby food items comprised diatoms, detrital material, filamentous algae and inorganic sediment. The relevance of this information in aquaculture is discussed. The stomach contents of adult Liza subviridis taken from different habitat types were consistent, comprising diatoms, detrital material and inorganic sediment. Filamentous algae was also consumed where available.     

Effect of hypoxia on the content and stoichiometry of cytochromes in muscle of the gray mullet Liza aurata

The maintenance of the gray mullet Liza aurata under conditions of hypoxia (P(O2) 55-82 GPa) for 1-2 days led to a decrease of oxygen pressure in arterial blood by 47%, while in venous blood--by 28%. The mean muscle oxygen pressure decreased by 19.2%. The number of hypoxic and anoxic zones in muscle tissue decreased significantly, in particular in red muscle. The maintenance of the fish in hypoxic waters for 15 days led to a rise of the content of cytochromes in muscle and a qualitative readjustment of the mitochondrial respiratory chain manifested in an increase of the content of cytochromes a and a3 and a decrease of cytochrome b. In discussion, literature data are presented which support the described regularity.