Gill monogenean communities on three commercially important sparid fish in Omani waters

The prevalence and intensity of polyopisthocotylean monogeneans on the gills of three commercially important species of sparid caught in Omani coastal waters close to the city port of Muscat were determined and compared. Throughout May 2012 to April 2013, infections on bi-weekly samples of the soldier seabream, Argyrops filamentosus (Valenciennes, 1830), the king soldier seabream, Argyrops spinifer (Forsskål, 1775), and, the silver seabream, Rhabdosargus sabra were evaluated. From a total of 200 specimens (standard length of 26–52 cm), caught by line angling or by traps, at least three species of gill monogenean, namely Omanicotyle [Bivagina] heterospina, Heteromicrocotyla sp. and Microcotyle sp., were commonly encountered. Silver bream, which was infected by all three monogeneans, bore the highest infections (100% prevalence; mean intensity of 20.14 ± 0.92 parasites fish-1), whilst the soldier bream, which was infected only by O. heterospina had the lowest levels of infection (of the three sparids with 63.8% prevalence; mean intensity 5.8 ± 0.17 parasites fish-1). Comments on the distribution of monogeneans on each host are provided but to what extent this is influenced by water current speeds passing through the buccal and opercular cavities, gill morphology, parasite size, and / or the morphology and efficiency of the parasite’s attachment apparatus requires establishing and forms the basis of ongoing investigations.

Gill histology of Nile tilapia Oreochromis niloticus following chronic and acute exposure to ammonia

Ammonia is a common aquatic pollutant and is toxic to fish. The main nitrogenous compound excreted by fish is also ammonia, which may reach toxic concentrations in high-density fish culture, reducing growth and productivity. In this study, changes in gill structure and mucus cell distribution were examined when juvenile Nile tilapia, Oreochromis niloticus, were exposed to chronic and acute concentrations of ammonia. For chronic exposure, the tilapia were exposed to daily increments in ammonia concentration rising from 0 mg L-1 ammonia on Day 0 to 5 mg L-1 by Day 8; the experiment was terminated on Day 9. There were obvious histopathological changes to the gills over this period including hypertrophy and fusion and of the secondary lamellae. The mucus cell number in gill histology sections were observed to increase until Day 6 then decrease thereafter until the termination of the trial. For the acute exposure, juvenile tilapia were exposed to 5 mg L-1 ammonia for 5 hours. Hourly changes to the gills were monitored, with notable changes to gill filaments and an observed increase in the mucus cell number over the duration of the experiment.

Gill histology of Nile tilapia Oreochromis niloticus following chronic and acute exposure to ammonia

Ammonia is a common aquatic pollutant and is toxic to fish. The main nitrogenous compound excreted by fish is also ammonia, which may reach toxic concentrations in high-density fish culture, reducing growth and productivity. In this study, changes in gill structure and mucus cell distribution were examined when juvenile Nile tilapia, Oreochromis niloticus, were exposed to chronic and acute concentrations of ammonia. For chronic exposure, the tilapia were exposed to daily increments in ammonia concentration rising from 0 mg L-1 ammonia on Day 0 to 5 mg L-1 by Day 8; the experiment was terminated on Day 9. There were obvious histopathological changes to the gills over this period including hypertrophy and fusion and of the secondary lamellae. The mucus cell number in gill histology sections were observed to increase until Day 6 then decrease thereafter until the termination of the trial. For the acute exposure, juvenile tilapia were exposed to 5 mg L-1 ammonia for 5 hours. Hourly changes to the gills were monitored, with notable changes to gill filaments and an observed increase in the mucus cell number over the duration of the experiment

Gill monogenean communities on three commercially important sparid fish in Omani waters

The prevalence and intensity of polyopisthocotylean monogeneans on the gills of three commercially important species of sparid caught in Omani coastal waters close to the city port of Muscat were determined and compared. Throughout May 2012 to April 2013, infections on bi-weekly samples of the soldier seabream, Argyrops filamentosus (Valenciennes, 1830), the king soldier seabream, Argyrops spinifer (Forsskål, 1775), and, the silver seabream, Rhabdosargus sabra were evaluated. From a total of 200 specimens (standard length of 26–52 cm), caught by line angling or by traps, at least three species of gill monogenean, namely Omanicotyle [Bivagina] heterospina, Heteromicrocotyla sp. and Microcotyle sp., were commonly encountered. Silver bream, which was infected by all three monogeneans, bore the highest infections (100% prevalence; mean intensity of 20.14 ± 0.92 parasites fish-1), whilst the soldier bream, which was infected only by O. heterospina had the lowest levels of infection (of the three sparids with 63.8% prevalence; mean intensity 5.8 ± 0.17 parasites fish-1). Comments on the distribution of monogeneans on each host are provided but to what extent this is influenced by water current speeds passing through the buccal and opercular cavities, gill morphology, parasite size, and / or the morphology and efficiency of the parasite’s attachment apparatus requires establishing and forms the basis of ongoing investigations

Gill monogenean communities on three commercially important sparid fish in Omani waters

The prevalence and intensity of polyopisthocotylean monogeneans on the gills of three commercially important species of sparid caught in Omani coastal waters close to the city port of Muscat were determined and compared. Throughout May 2012 to April 2013, infections on bi-weekly samples of the soldier seabream, Argyrops filamentosus (Valenciennes, 1830), the king soldier seabream, Argyrops spinifer (Forsskål, 1775), and, the silver seabream, Rhabdosargus sabra were evaluated. From a total of 200 specimens (standard length of 26–52 cm), caught by line angling or by traps, at least three species of gill monogenean, namely Omanicotyle [Bivagina] heterospina, Heteromicrocotyla sp. and Microcotyle sp., were commonly encountered. Silver bream, which was infected by all three monogeneans, bore the highest infections (100% prevalence; mean intensity of 20.14 ± 0.92 parasites fish-1), whilst the soldier bream, which was infected only by O. heterospina had the lowest levels of infection (of the three sparids with 63.8% prevalence; mean intensity 5.8 ± 0.17 parasites fish-1). Comments on the distribution of monogeneans on each host are provided but to what extent this is influenced by water current speeds passing through the buccal and opercular cavities, gill morphology, parasite size, and / or the morphology and efficiency of the parasite’s attachment apparatus requires establishing and forms the basis of ongoing investigations.

Optimal density of Asian seabass (Lates calcarifer) in combination with the Omani abalone (Haliotis mariae), brown mussel (Perna sp.) and seaweed (Ulva fasciata) in a land-based recirculating integrated multi-trophic aquaculture (IMTA) system

An experiment was conducted to develop a land-based recirculating integrated multi-trophic aquaculture (IMTA) system using a combination of the Omani abalone (Haliotis mariae) and Asian seabass (Lates calcarifer) as fed species, brown mussel (Perna sp.) and seaweed (Ulva fasciata) as extractive species. Specifically, the study was carried out to determine the optimal seabass density (20, 40 and 60 individuals per 500-liter tank) on water quality and the growth and survival of the cultured species in the system. Sampling of all species was done every two weeks to check their growth. Water samples were taken every two weeks for analysis of ammonia, nitrite, nitrate, phosphate, and silicate. Measurements of temperature, dissolved oxygen and salinity were done daily. Growth of abalone and mussels were higher in fish densities of 20/tank and 40/tank, respectively, while growth and survival of seabass were not significantly different between densities. Biomass of seaweeds decreased during the experiment period. Temperature, dissolved oxygen and salinity were within optimum levels. Ammonia levels decreased as nitrite increased but in some cases it remained high while nitrates did not increase, indicating that nitrites were not converted to nitrates most likely due to the lack of efficient bio-filtration in the mussel tank

Bacterial Infection in Farmed Barramundi Juveniles, Lates calcarifer

In 2016, Barramundi, Lates calcaifer juveniles imported from Thailand to the aquaculture station at Sultan Qaboos University exhibited remarkable external clinical signs of losing scales, severe muscle necrosis, and ascites. Fin rot was also observed in the diseased fish. The mortality reached more than 90 % and it was assumed that certain bacterial species were associated with the diseased fish. The objective of the present study was to investigate the infection route of disease, revealing the causative agent and finding the most effective antibiotic treatment. The suspected pathogen vehicle was mosquito larvae in the outlet of the culture tank as bacterium was isolated inside the mosquito larvae. Primary, traditional phenotypic tests and the vitic test confirmed that the bacteria were pathogenic Aeromonas sobria and Lactococcus garvieae. Eight of the most commonly used antibiotics in the aquaculture industry was used for antibiotic susceptibility test. It showed that that Gentamycin was the most effective antibiotic while the most effective environmentally friendly source was henna, Lawsonia inermis, at a concentration of 10%

Mortality of the abalone Haliotis mariae (Haliotidae: Mollusca) in aquaculture

The Omani abalone, Haliotis mariae, is the only species of abalone found in Omani waters. Given the rarity of this species and the high price it can fetch on the market (US$ 150 kg-1 dry weight), the wild abalone fishery in the Dhofar region has been regarded as a valuable income source for the past decade. The present study was undertaken set to investigate the mortality of abalone held at the Mirbat Research Center, through bacteriological and histopathological based investigations and challenge tests. Only the adult wild abalone that had been kept for a year in the hatchery, visually, appeared to be clear of disease symptoms. Infected individuals typically were swollen around the mouth, had fluid tinged with blood, bubbles in the intestines, and, very weak adhesive strength. The foot area (muscle) of diseased animals was noticeably very soft and individuals that were seen lying upside down on the bottom of the tank subsequently died. On dissection, the intestinal organs released bubbles and a foul smelling odour. Identification of the isolated bacteria using various identification methods indicated that individuals were infected with Staphylococcus sciuri. Histopathology of infected individuals revealed spongiosis of the tissues with evident bacterial infection. Neither of these histopathological conditions were seen in healthy abalone. The study concludes that the bacterium Staphylococcus sciuri may be the likely cause of abalone mortalities

Mortality of the abalone Haliotis mariae (Haliotidae: Mollusca) in aquaculture

The Omani abalone, Haliotis mariae, is the only species of abalone found in Omani waters. Given the rarity of this species and the high price it can fetch on the market (US$ 150 kg-1 dry weight), the wild abalone fishery in the Dhofar region has been regarded as a valuable income source for the past decade. The present study was undertaken set to investigate the mortality of abalone held at the Mirbat Research Center, through bacteriological and histopathological based investigations and challenge tests. Only the adult wild abalone that had been kept for a year in the hatchery, visually, appeared to be clear of disease symptoms. Infected individuals typically were swollen around the mouth, had fluid tinged with blood, bubbles in the intestines, and, very weak adhesive strength. The foot area (muscle) of diseased animals was noticeably very soft and individuals that were seen lying upside down on the bottom of the tank subsequently died. On dissection, the intestinal organs released bubbles and a foul smelling odour. Identification of the isolated bacteria using various identification methods indicated that individuals were infected with Staphylococcus sciuri. Histopathology of infected individuals revealed spongiosis of the tissues with evident bacterial infection. Neither of these histopathological conditions were seen in healthy abalone. The study concludes that the bacterium Staphylococcus sciuri may be the likely cause of abalone mortalities