Diversity and genetic structure of freshwater shark Wallago attu: an emerging species of commercial interest.

Pakistan has natural freshwater resources acting as a hotspot for diverse fish fauna. However, this aquatic fauna is declining at an alarming rate due to over-exploitation, habitat degradation, water pollution, climate change, and certain anthropogenic activities. The freshwater shark, Wallago attu, is a popular edible catfish inhabiting these freshwater ecosystems. Habitat degradation, overfishing, and human activities are heavily impacting the natural population of this species. So, sound knowledge about its population structure is necessary for its proper management in natural waters. The current study involves utilizing two mtDNA markers (COI, Cytb) to assess the genetic structure and differentiation among W. attu populations of Pakistani Rivers. Genetic variability analysis indicated a high haplotype (0.343 ± 0.046-0.870 ± 0.023) and low nucleotide diversity (0.0024 ± 0.012-0.0038 ± 0.018) among single and combined gene sequences, respectively. Overall, River Indus was populated with more diverse fauna of Wallago attu as compared to River Chenab and River Ravi. Population pairwise, Fst values (0.40-0.61) were found to be significantly different (p < 0.01) among three Riverine populations based upon combined gene sequences. The gene flow for the combined gene (COI + Cytb) dataset among three populations was less than 1.0. The transition/transversion bias value R (0.58) was calculated for testing of neutral evolution, and it declared low genetic polymorphism among natural riverine populations of Wallago attu. The current study's findings would be meaningful in planning the management and conservation of this economically important catfish in future.

Relative expression levels of growth hormone gene and growth rate in Indian major carp species.

The phenomenon of growth is a leading factor for aquaculture success. The uneven growth of major Indian carps (Labeo rohita, Catla catla, and Cirrhinus mrigala) is a serious issue in fish culture from an economic point of view. The growth hormone (GH) gene is crucial for selection in commercially cultivated fish species for better growth and production. Indian major carp (L. rohita, C. catla, and C. mrigala) are commonly cultured in Pakistan. The GH expression was examined using qPCR to understand growth in fish species better. Muscle tissue samples (n=480) from 160 individuals of the same age were collected from three species (L. rohita, C. catla, and C. mrigala). Individuals were divided into two groups (high-weight and low-weight groups), cultured under normal conditions. The housekeeping gene ß-actin validated GH expression in fast and slow-growing fishes from the same species. Results showed that GH expression varies across species and fish specimens that overweight their counterpart feature have higher GH expression. A selection for overweight fish in the aquaculture breeding systems is preferable as those fish could inherit their genomics to the future cohort, enhancing production, and commercial profit for farmers. Comprehensive research about different growth genes and the environmental aspects that influence fish growth is mandatory. No work has been reported regarding the growth gene analysis of fish from Pakistan. This report was Pakistan's first and baseline study regarding growth analysis of main culturable fish species at the molecular level.