Iranian Journal of Ichthyology
Volume:8 Issue: 4, Dec 2021

Fisheries is one of the main divisions in the Omani economy, providing about 54968 direct employment in 2020, and the costal sardine fisheries make a major contribution to the country's income. In this study, the fluctuations in abundance of the sardines especially Indian oil sardine Sardinella longiceps, a tropical small pelagic clupeid fish, was investigated during the years 1995 to 2020 in Oman. The results reveal that Oman fisheries including sardine stocks show fluctuations during the last 26 years (1995-2020), showing two periods of recession (1995-2011) and upturn (2012-2020). In the second period, small pelagic landings, mainly sardines, increased dramatically in Oman starting from 2012 (about 70,697 t), reaching a peak of 530,022 t in 2020. This reveals that the Omani small pelagics were heavily targeted during the last 10 years. However, so far, the small pelagic fisheries are not managed and there is a need for an urgent conservation and recovery plan before it is too late. In India, sardine landings were reported as high as a half million tones before it dropped to less than 55 thousand tons only in 2012, a scenario that could repeat itself in Oman in near future. To overcome this, sardine landings must be maintained according to the identified sardine’s biomass per given region, fishing effort must be carefully controlled and defined via a licensing system, sardine fishery must be closed every three years for at least one year to allow a fully recovery sardine stocks, reproductive biology, population dynamics and food and feeding habits of sardines should be studied in details and population size of jellyfishes which are larval and young fish predators of sardines should be monitored.

This study documents the occurrence of the exotic Suckermouth armoured catfishes (Loricariidae) of the genus Pterygoplichthysspp. in the Sri Lankan reservoirs. As little is known about the taxonomic status of the alien Pterygoplichthys spp. in Sri Lankan inland waters, this study was conducted based on the specimens collected in four distinct reservoirs in Kala Oya basin, North central province of Sri Lanka. The different morphometric measurements and meristic counts of current study reveals that suckermouth armored catfish, previously reported as Pterygoplichthys multiradiatus (Orinoco sailfin catfish), actually belong to the two different species-Pterygoplichthys disjunctivus (Vermiculated sailfin catfish) and Pterygoplichthys pardalis(Amazon sailfin catfish). Although the current examination describes two different species as above, some wild populations may probably be hybrids. In recent past there is a high concern on these species due to rapid range expansion and the effects on native ichthyofauna and inland fisheries resources. Therefore, implementations of effective management options of these species are highly recommended in native condition.

The present study investigates effects of stocking density of Bagrid catfish,Chrysichthys nigrodigitatuson the growth performance, feed utilization, proximate composition and water quality. Fish withaverage weight of 7.34±2.36g werestocked in triplicates at densities of 20 fish/m3(SD 20), 40 fish/m3(SD 40), 60 fish/m3(SD 60) and 80 fish/m3 (SD80). Fish were fed twice a day to apparent satiation for 8 weeks. The results showed that growth performance parameters such asfinal length, final weight, specific growth rate (SGR), percentage weight gain (%WG), weight gain (WG), and average daily weight gain (ADWG), were significantly different amongst treatments. The highest growth values were obtained in group SD 40 and the least values were obtained in group SD 80. Fish stocked at SD 40recorded the best feed conversion ratio, protein efficiency ratio and feed efficiency. Condition factor increased with stocking density but only from density SD 20 to SD 60 and decreased at SD 80. Water quality parameters were not significantly different among treatment except for nitrate but were all within acceptable ranges for fish culture. There was significant difference in coefficient efficient variation of final weight. There was no significant difference in proximate composition among groups. For optimum growth and feed utilization, this study recommends 40 fish/m3as the best stocking density for Bagrid catfish.

The article presents the results of ichthyological research on a large water body of the Kuma reservoir -the Pyaozero Lake. The fish population of the lake includes 16 fish species, representatives of 9 families belonging to 5 faunistic complexes. The salmonids and carp-like fishes (Salmonidae and Leuciscidae) dominate by the number of species (4 species each). The subdominant species are whitefish, and perch. The fish population is formed by the fish species of the boreal plain, arctic freshwater, and boreal foothill complexes. The lake has favorable conditions for the brown trout Salmo trutta, whitefish Coregonus lavaretus,vendace Coregonus albula(Salmonidae), pike Esox lucius(Esocidae), bream Abramis brama, roach Rutilus rutilus(Leuciscidae) and perch Perca fluviatilis(Percidae). The population and ecological analysis has shown a relatively favourable condition for most of the species studied in terms of size and mass. The pike in terms of size-mass indices (length and weight) is now smaller than in the middle of the last century. At the same time, pike has experienced a decrease and roach and increase in maximum life age now compared to the 1950s. There has been a shift in the sex ratio towards females in whitefish, bream, perch, roach, and vendace. This is probably a result of the decline in the populations of these species in the lake. In the Pyaozero Lake, of the biggest commercial values are vendace, perch and whitefish dominating in the research catches. The proportions of roach, bream, and pike were high. The most valuable commercial species, brown trout), is caught in single specimens. To maintain the structure and condition of the fish population in the Pyaozero lake, a set of measures is required, including conservation and improvement of habitat, reproduction, and feeding conditions; tightening of protection measures with declining numbers of fish species e.g., trout, whitefish and bream, regulation of fisheries and increase in artificial reproduction, cultivation, and introduction of native stocks.

In the present study, population characteristics of Scomberomorus commerson were evaluated by sampling fish at five fish landing sites in the northern Oman Sea (Iran) including Beris, Ramin, Pozm, Konarak and Jask from March 2017 to March 2018. The biometric analysis was performed on more than 11000 fish specimens. Growth and mortality indices were calculated including infinite length (L∞= 165 cm), growth coefficient (K= 0.5 (yr-1)), growth performance index (Ф= 4.13), natural mortality (M= 0.75(yr-1)), fishing mortality (F= 2.49 (yr-1)), total mortality (Z= 3.24± 0.15(yr-1)) and exploitation coefficient (E = 0.77 (yr-1)) as well as length time at time zero (-0.2). Relative production per recruitment, relative biomass per recruitment and exploitation rate of S. commerson were Y'/Rp= 0.06, B'/Rp= 0.32 and U= 0.65, respectively. The Pobj value is <1, and Popt and Pmega >0, the fishery show considered undesirable. The present study showed that the narrow - barred Spanish mackerel had undesirable stock condition and fish stocks have reached 'overfished' status. Therefore, specific measures should be taken to reduce catch and fishing effort.

In this study, we have studied the length-weight relationship, condition factor (Kr), gonado-somatic index (GSI) and size at first maturity of two Cichlidae species (Tilapia zillii andHemichromis bimaculatus) from two lakes (Megarine and Temacine) of the northern Sahara (Algeria). Some 159 specimens of H. bimaculatusand 52 T. zilliiwere sampled between September 2012 and July 2013. The length-weight relationship revealed an isometricvalue b (3.0) for H. bimaculatusfrom Lake Megarine, while there was no significant difference for T. zilliifrom Lake Temacine. We noted a negative allometric growth pattern (b<3) of males and females of H. bimaculatus. Both sexes of T. zilliigrew isometrically. The Kr did not differ significantly between months for the two studied species. It was less than 1 only in November and July for H. bimaculatus. For T. zillii, the monthly mean of Kr was always greater than 1 for all the studied period. The firstsexual maturity of 50% of males was observed at 52.75mm in H. bimaculatusand 61mm in T. zillii. The smallest mature female had a total length of 60.26mm and 66mm for H. bimaculatusand T. zilliirespectively. The reproduction period of H. bimaculatusandT. zilliibegins in March with an extended spawning period. The overall sex ratio was in favor of females (1: 0.7) in H. bimaculatus, and in favor of males in T. zillii(1: 1.33). For both species, the sex ratio varied according to months and size classes.

The Blackspot Barb, Dawkinsia filamentosa(Valenciennes, 1844), is a shoaling fish of India. As in many ostariophysians, alarm cues released after skin injuring elicit striking anti-predator behaviour in conspecifics. The alarm substance necessary for testswas obtained from a single donor specimen (female). Each fish was tested individually (in visible light or with IR illuminators)in anaquarium with size: 105×8×20cm; water height: 8cm. The tank was subdivided in 9 parts and the stimulation (water or alarm substance) was released just under the water surface at the higher posterior right edge: the elongated shape of aquarium allowed evidencing a possible avoidance response. Fish were tested in light or dark conditions both in absence or presence of a chemical alarm cue. In both test conditions, fish behavior was monitored with a camera, which was sensitive to both infrared and visible light. In each of two experimental conditions, 12 tests were conducted. In each test, 3 consecutive registrations were made: 15 minutes in absence of stimulus, 15 minutes after administration of 50 ml of pure water, and 15 minutes after administration of a solution of 48 ml of water and 2 ml of alarm substance. Each sector of tank was correlated with a number in crescent orderfrom 1, where administration was being carried out, to 9, in the opposite side. In each 15 minutes part of a test, fish position and associated number were relived every 30 seconds and the medium score of each fish obtained in absence of stimulus, in presence of water, and in presence of alarm substance were calculated. The medium scores obtained in presence of water and in presence of alarm substance were subtracted from the medium score obtained in absence of stimulus, obtaining a Changing Spatial Use Index. Indexes obtained for each fish (in presence of alarm substance and in presence of water) were compared with Wilcoxon test. As in others cyprinids, Blackspot Barbfright reaction differs in light or darkness. In particular, its alarm reaction in darkness seems to consist simply in moving to the bottom without any swimmingrapid movements and without any avoidance component of the alarm substance.

This study aimed to review the results of the introduction of tilapia and its impacts and consequences on the biodiversity of inland freshwaters of Iran as a baseline to help ecologists and aquaculturists for making a proper decision in this regard. Up to now, four invasive tilapia species viz. Coptodon zillii, O. niloticus, O. aureus, and Amatitlania nigrofasciatahave been reported from Iranian inland waters. Introducing tilapia species to the inland waters of Iran will have many severe impacts e.g. it will be possible to hybridize with endemic cichlid species such as Iranocichla hormuzensisand I. persa. The Iranian Fisheries Organization is executor and supervisor of aquaculture programs. It has implemented the development of tilapia farming regardless of the situation of the inland waters of Iran. Unlike many countries, Iran is an arid and semi-arid country with highly sensitive and fragile aquatic ecosystems which have more than 100 endemic species. Any change in the status of these aquatic ecosystems severely threatens their biodiversity. It is almost impossible to remove invasive tilapia species from Iranian inland waters in the currentsituation. Hence, the only possible solution in the current situation is to adopt an integrated approach to the management of aquatic ecosystems and close the pathways for the further spread of invasive species. This can be done through continuous and comprehensive cooperation between responsible organizations such as the Iranian Fisheries Organization, the Environmental Protection Agency, NGOs and local people