Age analysis and growth patterns of Tenualosa ilisha using otolith examination and length-weight relationships from different regions of Bangladesh
The assessment of age and growth patterns provides crucial information on numerous aspects of the population dynamics in fish, which can, in turn, be used to determine a sustainable fishing rate and inform effective resource management practices. However, studies on the age and growth pattern of Tenualosa ilisha (commonly referred to as hilsa) are plagued by a lack of essential information; addressing this data gap is the aim of the present study. Six diverse habitats across Bangladesh were chosen as sampling sites for hilsa collection. For age determinations, the lunar rings in the otolith of the hilsa fish that are periodically-deposited in accordance with the lunar cycle were used to reflect 14-day increments of time. The length and weight of each fish were recorded prior to otolith extraction. The resulting otoliths were polished to enable the visualization and quantification of their lunar rings with a high-magnification microscope. Except for the Kali River and Gaglajur Haor samples, the age of the fish correlated strongly with both their length and weight (r > 0.95; p < 0.05). Again, aside from those from the Kali River and Gaglajur Haor, all of the samples exhibited positive allometric growth patterns (b > 3) with the fish from the Tetulia River being the most positive (b = 3.48). The causes these variations are not yet clearly understood, however; the nutrient availability, environmental variation, and genetic-environmental interactions are likely contributors to the diversities displayed by the hilsa from different regions of Bangladesh.