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Blacktip Sea Catfish (Plicofollis dussumieri) is one of the most abundant commercial species along the coast of the Oman Sea. In this study, with the aim of an investigation some biological parameters of Blacktip Sea Catfish using gillnet and purse seine in coastal waters of Sistan and Baluchistan province (Oman Sea). Sampling was conducted from January to March 2020 and 818 P. dussumieri were collected using gillnet and 300 P. dussumieri were collected using purse seine and the fork length range of P. dussumieri was 22.10-62.10 cm and 17.30-10.37 cm in gillnet and purse seine, respectively. The Asymptotic length (L∞) was estimated at 64.41 cm and the optimal catch length was 34.41 cm. The length maturity (Lm50) of P. dussumieri was calculated to be 32.5 cm. The results show 38.10% of the fish caught were immature and did not have a chance to spawn. Most of the P. dussumieri that were caught by purse seine were smaller than length at maturity (Lm50). Obtaining such parameters with studies and long-term planning of these stocks and the information related to the length frequency, Asymptotic length, optimum catchable length and length at maturity can have a great impact on the knowledge of the stocks and fishing pressure on aquatic stocks such as P. dussumieri in Sistan and Baluchistan province.

Black Pomfret (Parastromateus niger) is one of the most important commercial species along the coast of the Oman Sea. In this study, the length frequency, weight, length-girth relationship, infinite length (L_∞) and optimum length were investigated in the coastal waters of Sistan and Baluchistan. Sampling were carried out from November to December 2020. The length range of Black Pomfret was 18-45.40 cm and its optimum length was 29.6 cm. The minimum and maximum weight was 112-1900 g with a mean weight of 396.453 g in Black Pomfret. The length-weight relationship of Black Pomfret was calculated as W= 0.0094TL3.2016. The correlation coefficient (R2) was 0.9622. The results showed that the calculated value of b parameter (3.2016), which indicates the natural growth of this species in Oman Sea, is positive allometric. The total length-girth relationship of Black Pomfret was calculated as Gmax=1.0555Gg+1.7124. The correlation coefficient (R2) was 0.9247. The L_∞was estimated at 47.3 cm. The length maturity (Lm50) of Black Pomfret was calculated to be 26.6 cm, and 65% of the fish caught were immature and did not have a chance to spawn. With studies and long-term planning of these stocks and the information related to the length frequency, weight, length-weight relationships, length-girth relationships and optimum length can have a great impact on the knowledge of the stocks of these fish and reduce fishing pressure on aquatic resources such as black Pomfret in Sistan and Baluchistan province.

The selectivity of greater lizardfish (Saurida tumbil), which is one of the most abundant economic species caught by gillnets in the northeast of the Oman Sea, Iranian waters, was studied. Sampling was conducted from February to March 2021. Four types of gillnets with mesh sizes of 4.8, 6.3, 10.0, and 15.3 cm were used and 857 fish specimens were collected. The catch patterns, including (snagged, gilled, wedged, and entangled) for S. tumbil were observed in gillnets. For 4.8 and 6.3 cm mesh sizes, more than 70% of the catch was mainly obtained by gilled, followed by wedged, and no found of entanglement. For 10.0 and 15.3 cm mesh sizes, the catch of 10.0 mesh size included 16% of fish caught from wedging, though most of the fish was caught by entanglement. In particular, all catches at 15.3 cm were due to entanglement. Estimation of gillnets selectivity for S. tumbil was performed using the SELECT method. The SELECT method was used to fit three various gillnet selectivity models (log-normal, skew-normal, and bi-normal). Gillnets selectivity was best estimated by a bi-modal Selection curve. The mean lengths ±SE were estimated as 31.48±0.71, 40.3±0.97, 40.1±0.75 and 43.9±1.05 cm for 4.8, 6.3, 10.0 and 15.3 cm mesh sizes, respectively. Mean lengths increased with increasing the mesh size. Most of the fish caught in the 4.8 and 6.3 cm mesh sizes were below the first maturity length (Lm50). Considering the relative efficiency set as 0.5, that was L50 (50% retention length), the optimal mesh size was determined to be 10.0 cm. Therefore, to protect S. tumbil stock and the sustainability of the fishing resource, the gillnet mesh size should be at 10.0 cm to manage S. tumbil in this area.