Competition between mullet fry

The fry of Liza ramada, L. aurata, L. saliens, Chelon labrosus and Mugil cephalus in a lagoon in NE Spain fed mainly on zooplanktonic crustacea, such as cyclopoids, calanoids and cladocerans, but adult chironomids were also important. A high trophic and temporal overlap was found between the fry of several of these species. Trophic overlap was asymmetrical for almost all the species pairs and niche breadth expanded for the less competitive species when they were alone in the estuary. In contrast, niche breadth did not expand for the most competitive species ( L. ramada ) when it was alone. These results suggest that competition was occurring among these species, but experimental evidence is needed to prove its existence.     

THE USE OF BENZOCAINE HYDROCHLORIDE AS FISH TRANQUILLIZER AND ANAESTHETIC IN SALINE WATERS

SUMMARY

The anaesthetic effects of various concentrations of benzocaine hydrochloride were tested on Liza macrolepis and Sarotherodor mossambicus in sea water and diluted sea water, respectively. Induction time for anaesthesia was negatively correlated with increasing anaesthetic concentrations in L. macrolepis.

In S. mossambicus, however, operculum clamping appeared to be responsible-f or induction times increasing with increased anaesthetic concentration.

The tranquillizing effects of low concentrations of benzocaine hydrochloride on L. macrolepis was also studied.     

渤海莱州湾渔业资源增殖的敌害生物及其对增殖种类的危害

根据近岸捕食鱼类胃含物分析及渤海生物资源大面积定点拖网调查 ,研究了渤海莱州湾渔业资源增殖的敌害生物种类、分布及其对增殖种类的危害 .结果表明 ,鲈鱼幼鱼、黄姑幼鱼、绵鱼尉、虾虎鱼类是捕食渤海对虾、梭鱼等增殖种类幼体的主要敌害生物 ,危害主要发生在近岸 ,其中鲈鱼危害较为严重 ,主要危害期为 7月 ,被捕食的幼对虾长度以 3～ 7cm为主 .鉴于敌害生物大量捕食增殖种类主要发生在近岸和两者密集分布区的重叠处 ,在增殖放流区选择上 ,对敌害生物采取“回避”策略是保护增殖放流种类的可行措施 .     

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.     

内蒙古主要植被类型与气候因子关系的研究

利用地理信息系统工具,以最新的植被类型图为依据,在统计、建模和空间模拟区域气候因子的基础上,对内蒙古主要植被类型与气候的关系进行了分析,并获得适宜的气候范围.结果表明,内蒙古植被空间分布表现出明显的规律性.一方面,随着距离海洋的远近变化,无论是地带性植被,还是山地垂直带、沙地及低湿地植被,从东向西均反映出地带分异,水分对于这种东西向更替更为重要.另一方面,热量的差异导致纬向上的变化.此外,热量成为大兴安岭东西两麓发育的林缘草甸、草原、灌丛和低湿地等植被类型空间分布的主导因素.     

Molecular markers for identification of Stellantchasmus falcatus and a phylogenic study using the HAT-RAPD method

Stellantchasmus falcatus is a minute intestinal fluke in the family Heterophyidae. Metacercariae, the infective stage, were reported in a marine fish, mullet Liza subviridis, and a fresh water fish, Dermogenus pusillus, in Thailand. Adults were found in chicks, rats, cats, and humans. Morphological studies were done for comparing Stellantchasmus sp. worms found in 2 different fish hosts; their shapes and organ arrangements were very similar except for the prepharynx length. Therefore, the present study aimed to compare their DNA fingerprints using the HAT-RAPD method for both types of Stellantchasmus and several other related species. Ten arbitrarily selected primers (OPA-04, OPA-09, OPN-02, OPN-03, OPN-09, OPN-12, OPP-11, OPR-15, OPX-13, and OPAD-01) were used. It was found that OPA-09, OPN-03, and OPAD-01 were able to generate S. falcatus specific fragments in mullets which consisted of 200, 760, and 280 bp, respectively. In addition, the results of morphologic, DNA fingerprinting, and phylogenetic analyses strongly suggest that the fresh water and marine specimens of Stellantchamus may be different species.     

The feeding strategies of Liza ramada (Risso, 1826) in fresh and brackish water in the River Tagus, Portugal

The stomach contents of samples of the mugilid Liza ramada (Risso, 1826), captured at Alcochete (brackish water zone of the Tagus Estuary) differed from those from Vala Nova (freshwater zone of the same estuary).
In the freshwater zone of the estuary the mullet ingested preferentially planktonic micro-algae, while in the brackish water they ate benthic micro-algae.
The stomach contents from Vala Nova showed a higher diversity of food items, compared with those from Alcochete. At Alcochete the Naviculales (numerical frequency, 82%) was the most representative order, while at Vala Nova it was the Coscinodiscales (61%) and the Chlorococcales (16%).
In fresh water, the stomach contents contained about 25–4% organic matter, while at Alcochete only 8.7% was found.
In the brackish water zone the ingestion rhythm was related to the tidal cycle, attaining a maximum during the high tide and a minimum at low tide.
At Vala Nova the mullet ate regularly throughout the day. showing a slight increase at dawn and dusk. Apparently, the fish remained inactive by night, at both locations.     

Non-competitive coexistence between Mediterranean grey mullet: evidence from seasonal changes in food availability, niche breadth and trophic overlap

Five grey mullet species in the Albufera des Grau lagoon (Balearic Islands, Western Mediterranean), reacted to the spring-summer reduction in the organic matter content of sediment by expanding their niche breadth, mainly due to higher algae consumption. However, trophic overlap did not change for most of the studied species pairs and when it did, overlap was higher in the warm than in the cold season. When all the assemblage was considered, niche overlap distribution was significantly skewed towards values higher than those predicted by null models, both in the warm and the cold season. These results are not consistent with the predictions from the niche theory, which suggests that grey mullet are under carrying capacity and hence competitive exclusion does not operate in the studied assemblage.     

梭鱼早期发育阶段体色形成与鳍的分化

采集池塘育苗的39日龄之前的梭鱼(Liza haematocheila)仔、稚、幼鱼,对其早期发育阶段体色的变化以及鳍的发生、发育进行了连续观察。初孵仔鱼体表不具黑色素,仅卵黄囊具黑色素,孵化后2日龄体表黑色素增加,鳍膜无色透明。8日龄仔鱼开始变得不透明,腹侧有黑色线状斑点。在18~19日龄仔鱼转化为稚鱼时,鱼体背部具大量雪花状黑色素颗粒,在透色光下可观察到淡黄色斑点(黄色素)。30日龄幼鱼与成鱼相似,体表具淡白色,背褐腹白。梭鱼仔鱼在早期发育阶段各鳍的发育顺序是:胸鳍→尾鳍→腹鳍→背鳍→臀鳍→第二鳍棘。初孵仔鱼,鳍褶从头部后缘向后绕过尾部,终止于卵黄囊后缘油球外侧。2日龄仔鱼具胸鳍芽,全身由鳍膜包裹,5日龄仔鱼胸鳍和尾鳍鳍膜已具有相当的运动能力,能够起到推动和维持身体平衡的作用。梭鱼鳍在早期发育过程中最明显的变化是尾鳍的生长和鳍节的发育。梭鱼仔鱼在12日龄时出现腹鳍棘芽基,15日龄时第二背鳍棘出现。17日龄,尾椎骨向上弯曲,尾鳍基本发育完成,长鳍条16根,具10节,中间几根棘条末三节二向分叉,短鳍条上下各6~8根;背鳍有鳍条11根,具5节,最外侧鳍棘具刺,基部有支鳍骨。至30日龄,梭鱼幼鱼各鳍发育完全,与成鱼相似。