Sexual Dimorphism, Length-Weight Relationships, Fecundity, and Diet of the Striped Eel Catfish Plotosus lineatus (Plotosidae) on Taiwan’s Southwest Coast

This study of feeding guild fish from the same coast of subtropics helps to suggest conservation of fishery resources. A total of 2,537 specimens of Plotosus lineatus (Plotosidae) were collected from July 2013 to March 2019 on the coast of Taiwan. The average total body length (TL) was 23.7 cm ± 4.7 cm and 20.3 cm ± 2.9 cm, and the average body weight (W) was 94.1 g ± 59.6 g and 56.6 g ± 30.8 g among 174 males and 630 females, respectively. The LWRs of male and female were ln(W)M = 3.2914 × ln (TL) −6.0395, and ln(W)F = 3.0917 × ln(TL) −5.3629. The male specimens were large than female in TL and W. The average OSW/TL ratios were 0.722 ± 0.044 and 0.649 ± 0.029 among 41 male and 49 female specimens, respectively. The OSW of the male head was wider than that of the female head (F = 91.5;p < 0.001), and the head widths of the male fish were significantly more than those of their female counterparts, causing the OSs to form granular protrusions. The average CFW/TL ratios were 0.198 ± 0.034 and 0.252 ± 0.032 among the male and female specimens, respectively. The CFW of the male specimens was narrower than that of the female specimens (F = 58.9;p < 0.001), and the CF gap of the male fish was narrower than that of the female fish. The P. lineatus exhibits significant sexual dimorphism. The average eggs number of each female was 2375.6 eggs/individual ± 1140.9 eggs/individual (N = 161). The major prey of P. lineatus were shrimps, crabs, and fishes;the total relative frequencies of occurrence of the prey were 57.1%, 32.6%, and 37.2%, respectively (N = 282), and their total relative abundance levels were 40.2%, 26.3%, and 25.8%, respectively (N = 445). Proper scientific knowledge management will improve the development of fisheries.

Population Structures and Diets of Two Species of <i>Pisodonophis</i>(Ophichthidae) from the Southwest Coast of Taiwan

This study was used to lift nets and trap net fishing at intertidal zone of lagoon and estuarine regions of southern Taiwan. From July 2013 to July 2018, a total 420 specimens of Pisodonophis were analyzed, the average total body length (TL) and average body weight (W) of P. boro eels are 68.4 ± 11.9 cm and 140.4 ± 86.1 g (N = 194), respectively. Typically, P. cancrivorus eels are smaller (TL = 52.8 ± 9.2 cm) and lighter (W = 107.9 ± 73.7 g [N = 119]) than P. boro eels. The natural logarithmic linear relationships between the TL and W of P. boro and P. cancrivorus are respectively expressed as ln(W)b = 2.4405 ln(TL) − 5.4448 (R2 = 0.796, N = 194) and ln(W)c = 3.2168 ln(TL) − 8.2027, (R2 = 0.934, N= 119). P. cancrivorus typically preys on shrimp, crab, and fish;lab assessment revealed that the frequencies of occurrence of these foods in their guts were 49%, 21%, and 15%, respectively (N = 100). The main catch months of P. boro were during the rainy season, and that of P. cancrivorus were the winter season in Taiwan. The average W values of P. boro from Jhuoshuei and Puzih estuaries were 343.2 ± 218.8 g (N = 91) and 140.4 ± 86.1 g (N = 194), respectively. Furthermore, the results of the study revealed that the Puzih estuary is overfished. We suggest that fishery management units should develop some protection measures for the conservation of aquatic ecosystems in estuarine regions. For example, the P. boro weighing less than 113 g will be released back to the estuary.

Sand Grain Size and Organic Matter Concentration in the Intertidal Zones on the Southwest Coast of Taiwan

From April 2013 to April 2014, the average pH and water temperature of the Taisi oyster cultivation area (TS, Yunlin County, Taiwan) were 8.05 (7.35 - 8.45) and 24.7˚C (13.7˚C - 32.8˚C) (N = 8226) The average organic matter (OM) concentration at sites TS-A and TS-B were 6.9% ± 1.3% and 6.9% ± 1.2%, and the weight of drift sand was 40.3 ± 19.1 g/d/m2 and 28.5 ± 34.3 g/d/m2 (N = 27). Considerable sand drifting typically occurs during the southwest monsoon season in summer. The average OM concentration at five dunes from Zhuoshui estuary to Zengwun estuary was 23.9 ± 4.5 g/kg. The percentage of sand grain weight of 0.15 - 0.25 mm and 0.25 - 0.60 mm was 82.5% ± 14.2% and 10.5% ± 12.0%. In the spring and autumn of 2015, the average OM concentration at the eight intertidal zones from Hanbao to Cigu was 49.8 ± 34.1 g/kg (N = 177), and the OM concentrations at Huwei estuary and Hanbao and Fangyuan intertidal zones were relatively high. The OM concentration (95.3 ± 75.7 g/kg) of the low tide zone of Huwei estuary was the highest among all tidal zones. The OM concentration during spring (59.4 ± 41.7 g/kg, N = 95) was higher than that in autumn (39.1 ± 17.8 g/kg, N = 84). For sand grain size ranges 0.15 - 0.25 and 0.063 - 0.15 mm, the weight ratio of intertidal sediment was 39.4% ± 26.9% and 27.6% ± 20.1%, respectively. The broad and flat intertidal zone was marked by fine sand and long intertidal zone;the weight ratio of SGSs < 0.25 mm exceeded 65%, and the OM concentration was between 20 and 30 g/kg. Coastal habitat diversity creates differences in biological communities, especially among crabs and benthic organisms. A greater understanding of coastal environments can aid in the management of coastal wetlands.