View Crossmark dataFrontiers in Life Science, 2015 Vol. 8, No. 1, 71-96, http://dx.doi.org/10.1080/21553769.2014 The fishery, biology, growth and stock structure of Euthynnus affinis is studied in detail. Hooks and lines, gillnets and purse seines are the major equipment used to exploit the fish. Fisheries are sustained mainly by 1-2 year old fishes (34-50 cm). Spawning was observed around the year with peaks during July-August and November-January. The length-weight relationship is 0.0254 L2.889 with no significant difference between males and females. Age and growth are estimated using length based methods. The maximum sustainable yield estimated was higher than the average annual catch, indicating scope for further exploitation. Elevated levels of heavy metals in Euthynnus affinis may be a good indication of pollution of an aquatic ecosystem due to anthropogenic influences. A total of 278 fishes were collected from Karachi coast, Fish Harbor West Wharf, Karachi, for metal (Cd, Pb, Zn and Cu) analysis in the organs of the fish. The metal levels in the sample fishes are in descending order of toxicity Cd > Pb > Zn > Cu. In the risk assessment, we assessed potential human health risks associated with consumption of fish, incorporating information gathered during a year-long, intercept-style creel angler survey and representative heavy metal concentrations in fish tissue. Fishing operations can cause ecological impacts of different types, e.g. by the catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, and generation of marine debris. Periodic reassessment of the tuna potential is required, with adequate inputs from exploratory surveys as well as commercial landings; this may prevent any unsustainable trends in the development of the tuna fishing industry in the Arabian Sea.

The present study was conducted to investigate the contamination of Fe, Mn, Cu, Zn, Ni, Pb, Cd, and Cr in the tissues of commercially important fish Thunnus tonggol and to evaluate risks to human health associated with seafood consumption. The results from this study showed that the concentrations of all metals measured except Cr were relatively high in the liver compared to the muscle, gills and gonads. High concentrations of Cr were present in the kidneys. Fe had the highest concentration compared with other metals tested in all tissues of followed by Cu and Zn. the present study revealed that all metals except Cu and Cd concentrations in the muscle tissues were lower than the maximum permissible limit as recommended by the international regulations. However, the estimated the Provisional Tolerable Weekly Intake (PTWI) of Cu is below the established PTWI. The data indicate that the examined fish were polluted with Cd. It was also found that levels of the metals in other tissues in some samples were higher than the recommended concentrations. However, consumers do not consume the liver, kidney, gills and gonads.

In the present study, Scomberomorus commerson was collected during the period 2006-2011 in order to provide information on the concentrations of eight heavy metals present in this marine species commonly consumed by the population and to have knowledge whether these levels may constitute a hazard to consumers. Liver showed high concentrations of metals in the tissues and organs. Fe is the most accumulated in all tissues and organs. The highest mean concentration of Fe (608.93+113.22 µg/g), Mn (9.79+4.22 µg/g), Cu (38.57+16.62 µg/g), Zn (53.25+26.50 µg/g), Ni (3.22+1.13 µg/g), Pb (1.20+0.64 µg/g), Cd (2.03+0.91 µg/g) and Cr (1.93 + 0.87 µg/g) was determined in liver of fish. The order of abundance of the metals in the fish samples based on concentrations in the muscle tissues analysed were as follows: Fe>Zn>Cu>Mn>Ni>Cd>Pb≥Cr. For the toxic metal, Pb was found to have lower concentration of the mean values than the permissible limits set by FAO/WHO. However, Cd level was higher than the permissible limit and it can be concluded that the contamination of Cd in S. commerson may pose threat for the importers due to high per capita consumption of the fish.

In this study, Nickel (Ni), Lead (Pb), Cadmium (Cd) and Chromium (Cr) concentrations were determined in muscle, liver, kidney, gills and gonads of Indian mackerel (Rastrelliger kanagurta) collected from Karachi fish Harbour, Karachi coast, Pakistan, during August 2006 and December 2011. Generally, the fish showed the highest level of Ni (2.26+0.89 µg g -1 ), Pb (1.45+0.40 µg g -1 ), Cd (2.07+0.75 µg g -1 ) and Cr (1.52+0.69 µg g -1 ) in the liver. The studied metals were the most abundant in the liver than the other organs of the fish. The amount of metal accumulation in fish tissues was evaluated in terms of human health. It was seen that bioaccumulations in muscle tissues of the fish caught from Karachi coast of Pakistan did not exceed the limit values.

Microplastics are one of the major pollution problems of nowadays, have been found in both marine environments and various fish species worldwide. In this study, the presence of microplastics in digestive systems and gills of 6 species from the Scombridae family on the coast of Karachi in Pakistan was investigated. A total of 336 fish were examined for the presence of microplastic in gills and digestive systems. Microplastics were detected in digestive systems and gills in 11.11%-19.51% and 58.62%-85.71% of total individuals, respectively. The amount of microplastic varied from 0.19 to 1.12 items.ind-1 in digestive system and 1.5 to 7.04 items.ind-1 in gill. Fibre was dominant both gills (98.67-99.17%) and digestive systems (100%). More extensive and further investigations are needed on microplastic contamination of the biota on Pakistan coast.