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Specimens of the portunid crab, Thranita crenata (Rüppell, 1830), commonly known as spiny rock crab or crenate swimming crab, were collected from Buleji rocky shore, in Karachi, during March 2015 to February 2016. The size (recorded as carapace width measured between the tips of the 5th spines) at which male and female crabs attain maturity was 42.6 mm and 42.4 mm CW, respectively. The smallest size of an ovigerous female crab was 38 mm CW. Although there were some more male crabs than female crabs in the samples, the male to female ratio was not significantly different from 11 (). Sex ratios in different size groups and different months were also found insignificantly different from a 11 ratio. Ovigerous females were found throughout the year, with a major peak in May and a minor peak in October when, respectively, 30.04% and 25.12% of the female crabs were ovigerous. The minimum and maximum fecundities recorded were 42 800 and 193 433 in females of 35 mm and 77 mm CW, respectively, and the average fecundity was 107 856 ± 50 331 over all berried females.

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The Indus River is proclaimed  as second most plastic-polluted rivers of the world. This river is the principal river of Pakistan and supplies freshwater for agriculture and human consumption. Its terminus into the northern Arabian Sea creates a unique ecosystem that supports a variety of aquatic organisms. In this study we have evaluate the heavy metal concentration in fishes sampled from the IRE. Muscle tissues from five fish species of ecologically and economically important were sampled and the concentrations of cadmium (0.125‒1.025 µg g−1, 0.93 ± 0.33), lead (0.250‒2.560 µg g−1, 0.92 ± 0.86), arsenic (4.178‒6.337 µg g−1, 4.24 ± 2.13) and mercury (BDL‒0.116 µg g−1, 0.05 ± 0.04) were found to be beyond optimum level. We determined the pollution load index which indicated that the IRE pollution exhibits significant seasonal oscillations. In addition to the heavy metal assay we note the frequent appearance of abnormal fishes caught in the IRE, which validates the pollution load. Multivariate approaches, canonical correspondence analysis and cluster analysis, were used to evaluate the relationships among environmental variables that influence metal concentration. This study is the first to document heavy metals detected from fishes inhabiting in IRE and highlights concerns regarding the need for management measures. Highlights We examined heavy metals in commercial and ecological valuable fishes in the Indus River Estuary (IRE) for the first time. Multivariate approaches were used to determine the efficacy of environmental parameters to predict heavy metal concentration. We described the presence of fish abnormalities as a result of contamination in the IRE. We observe that the mechanism of action of organism health and food contamination in the IRE is poorly understood.