International Journal of Aquatic Biology
Volume:9 Issue: 1, Feb 2021

The genetic diversity and the population structure of Barilius barna (Hamilton, 1822) wild population from the Teesta River were assessed through mtDNA cytochrome oxidase I (COI) sequence analyses. The haplotype and nucleotide diversity analyses revealed low level of genetic diversity in the B. barna wild populations, especially in the lower reaches of Teesta (Bholarhat). The genetic differentiation and gene flow between the two study sites were 0.08434 and 2.71, respectively. Tajima’s D, Fu and Li’s D and Fu and Li’s F analyses were used to assess population differentiation in the two study sites. Haplotype networking and phylogenetic analyses clearly distinguished the two populations from each other, as well as from other populations from other parts of the country. Nature and implications of the genetic and haplotype diversities among the populations are discussed. Phylogenetic analyses also indicated that the Gajoldoba population is genetically closer to north Indian river populations, than that to Bholarhat population.

Recently an article entitled “A unique sex chromosome system in the Knifefish Gymnotus bahianus with inferences about chromosomal evolution of Gymnotidae” has presented the chromosomal structure of a Gymnotus population inhabiting the Contas River basin, eastern Brazil. We believed that the examined specimens were misidentified as G. bahianus. Hence in this work we examined the used material of the above-mentioned work and found that they belong to the species G. interruptus. This conclusion was based on a careful examination of materials from both species (type, recently collected, and additional materials). Gymnotus interruptus can be distinguished from G. bahianus by possessing a colouration pattern in which conspicuous dark obliquely oriented bands occur under lateral line at entire extension of trunk.

Morphology of structures involved in the posterior region of scales in two flathead fish species viz. Platycephalus indicus and Grammoplites suppositus was studied using ultramicroscopy. The fish individuals were divided into three size groups based on their standard lengths and their scales were removed from four body regions. The microscopic observations indicated that the scales of both species were ctenoid. The posterior margin of all scales was formed by two rows of ctenii. Typically, the shape of the posterior region of scales in P. indicus was crescent, while it was triangular in G. suppositus. The number of ctenii in the scales of P. indicus was minimum 12 and maximum 60, while in G. suppositus it was minimum 6 and maximum 38. Moreover, the results indicated that the number of ctenii was increased during fish development because the smaller fishes have fewer ctenii in their scales than the adults, while, their general morphology has not been changed properly. This developmental change was significantly higher in P. indicus than G. suppositus. The increase of ctenii during fish development allows greater flexibility in movement. In conclusion, modification in the ornamentations of the posterior region has a hydrodynamic function and they are subject to modification during the fish development. The ctenii varying considerably in the number and could be easily counted, therefore, could be used as an appropriate taxonomic character at least in flathead fishes or even other fish groups.

Procambarus clarkii is a native species of Central America, but strongly invasive in many regions of the world. An investigation on the red swamp crayfish was carried out to obtain more information about its population dynamics in the Tiber River, in Central Italy. A total of 900 individuals, both males and females, were sampled within two different campaigns (2017 and 2019) aimed at collecting biometric data. A strong fishing effort was deployed (more than 100 nets set), to guarantee a large and randomized number of samples. The crayfish populations were grouped into seven different cohorts, according to Bhattacharya’s method. The population showed a balanced sex ratio, the average cephalothorax length was 42.52 mm, with the most represented size class between 40-50 mm. K and L∞, as well as the growth parameter index (Ø), the mortality rate (Z), and longevity value (tmax), were calculated. K and Ø values resulted very high, showing an impressive growth rate in the study area; tmax ranged from 4 to 5 years, L∞ values were lower compared with other studies (58.0-59.0 mm), while Z was very high for this population (4.2-4.5 year). The results revealed that crayfish population dynamics can be complex and vary depending on habitat type, available trophic resource and competition.

Capoeta baliki was described from Sakarya basin, Turkey. It was distinguished from its nearest congener i.e. C. tinca based on a combination of characters, including fewer serrae along posterior margin of last simple dorsal-fin ray, modally fewer scale rows between lateral line and dorsal-fin origin, fewer vertebrae, deeper and shorter head and slenderer caudal peduncle. We examined the synonymy hypothesis of C.  baliki and C. tinca by comparing their morphometric, meristic and molecular characters. Based on the results, their morphometric and meristic characters largely overlapped and no character was found to distinguish them. In addition, a low K2P mean genetic divergence of 0.37% C. baliki and C. tinca based on cytb gene and clustering in same clad showed that they are identical in molecular characters. As no character could be found to clearly distinguish these species, we treat C. baliki as a junior synonym of C. tinca.

The squeaker, Synodontis schall dominates the Mochokid fish sub-community in Niger River in Northern Benin and shows a great economic and commercial importance. The diet of S. schall has been analysed to evaluate the food habit and resource utilization in this regional River. Fish samplings were made monthly from February 2015 to July 2016 using unbaited longlines and traps, seines and experimental gillnets. The results indicated that S. schall is an omnivore foraging in benthic and pelagic habitats with diet dominated by aquatic insects (34.32%), sand particles (18.768%), macrophytes (13.415%), seeds (8.549%), roots (8.319%), detritus (5.344%), mollusks (1.204%) and phytoplankton (0.6255%). The omnivore food habit depicted was also shown by the ecomorphological analysis mainly the relative gut length (GL/SL) varying between 0.8 and 5. The species showed high diet flexibility with high niche breadth ranging between 1.86 and 5.74. Synodontis schall exhibited an ontogenetic diet shift that was also confirmed by Pianka’s diet overlap indexes ranging between Øjk=0.54-0.93. The conservation and the sustainable fisheries exploitation of S. schall require the reinforcement of fishing regulation, habitat protection and ecosystem follow-up.

Agrochemicals, also known as pesticides include nematicides, molluscicides, rodenticides, herbicides, fungicides and insecticides, can control pests, weeds, fungi, rodents, etc. The accumulation of pesticides in the food chain and water has harmful effects on humans and animals.  Despite the advantages provided by pesticides, aquatic organisms and human health are affected as the results of continuous usage of pesticides and issues of building up of chemical substances in aquatic organisms, such as fish. Pesticides must be lethal to the targeted species without any effect on non-targeted ones. Pesticides have harmful effects on the nervous system. Other pesticides are known to be carcinogenic substances. This review discussed the effects of pesticides on the immune system, protein, chromosomes, behavior, enzymes, growth, bioaccumulation, genotoxicity and changes in blood biochemical parameters of fish and humans and suggested some possible ways of mitigating such effects.

The olfactory structure of Xenentodon cancila (Hamilton, 1822) were explored by advancement in microtomy, staining and ultrastructural practices. The unique feature of the olfactory system was that the olfactory cavity, an open groove with an obtruding sole lamella, no rosette like organization. The lamella was constituted of the central core, lined on both sides by well-organized epithelium. The central core usually consisted of connective tissue fibres and blood capillaries. The epithelium exhibited compact cellular distribution and made up of receptor cells, supporting cells, lymphatic cells, inner most basal cells and almost never mucous cells. Morphologically specific two types of receptor neurons were recognizable: ciliated and microvillous, comprising sensory terminals. The cellular constitution of olfactory mucosa was explained with olfactory sensitivity of the fish necessitated.