Journal of Applied Ichthyology最新文献

Growth patterns and body condition of 10 species of Trematomus (family Nototheniidae) collected off the Antarctic Peninsula and in the Weddell Sea during seven cruises carried out between 2002 and 2022 were estimated by length–weight relationships (LWRs) and relative condition factors (K_rel). Most of the investigated species exhibited positive allometric growth, except for males of T. scotti and females of T. tokarevi, which showed isometric growth. Sex-related differences of slope (b) in the LWRs were recorded only in T. eulepidotus and T. scotti. No slope differences were found when comparing populations from the two sampling areas. The form factor, derived from the LWR parameters, was a reliable indicator of body shape and was consistent with the mode of life of each species. K_rel was evenly distributed around unity, although data dispersion differed among the species. The overall similarity of growth patterns and body condition among the different species of Trematomus was likely due to their genetic similarity and common life history strategies despite their wide spatial distributions and different modes of life.

Fisheries monitoring and research often requires preservation of fish samples for later analysis in the laboratory. Freezing is a common method, but it can affect subsequent fish size and composition, and the interpretation of metrics based on them. We evaluated the effects of freezing on fish wet weight, dry weight, and the percentage dry weight (a measure often used to estimate energy density). Specifically, we quantified changes in the weight of individual mummichogs (Fundulus heteroclitus) frozen at different temperatures (−20°C and −80°C) for 1–3 months. In addition, a temperature change treatment where fish were initially frozen at −80°C for one month before transfer to −20°C for an additional 1–3 months was included to simulate protocols typically used at sea. Individual wet weights were measured before freezing, and after freezing, the wet weights, dry weights, and percentage dry weights were determined. All freezing treatments resulted in minor but significant (p < 0.05) water loss. While the change was measurable and directional, it did not have a significant effect on the percentage dry weight except for samples held at −20°C for 3 months. A similar increase in percent dry weight was not evident in the temperature change group that was also stored at −20°C for 3 months. The least amount of weight loss, and therefore bias, was in the −80°C group, followed by the temperature change group, with the −20°C treatments losing the most water. The results indicate that if specimens for percent dry weight estimation have to be frozen, −20°C is okay for a short period of time (1–2 months), but when longer storage times are needed, −80°C is the best, even if only for the initial freezing period.

The length–weight relationship (LWR) in fish is an important tool because it allows understanding aspects such as growth assessment, body condition, and biomass estimation. The aim of this study was to determine the LWR of food fish species from the Amazonian plain of the Putumayo River caught by artisanal fisheries to be sold in the town of Puerto Leguízamo between 2018 and 2023. More than 19,000 individuals of 31 species were registered. Each fish was taxonomically identified at the species level, recording its standard length (cm) and weight (g). Searches in FishBase revealed that six species lack referenced data, twenty five are not reported for the Putumayo Basin, and five are in the vulnerable category, according to the International Union for Conservation of Nature (IUCN). The relationship data calculated in this study are the first publications for these species in this region of the Amazon Basin. Knowledge of these biometric data and their relationships is relevant for managing and conserving fish and fisheries.

This study investigates the reproductive biology, feeding habits, and growth pattern of Sillago sihama (N = 119) and Sillago mengjialensis (N = 18) collected from Cox’s Bazar, Bay of Bengal, between August 2022 and October 2023. The total length and body weight of S. sihama ranged from 72.19 to 173.50 mm and from 2.49 to 41.32 g, respectively, while they ranged from 78.32 to 159.81 mm and from 3.08 to 27.19 g, in S. mengjialensis, respectively. The sex ratio was male-dominated in both species. Peak gonadosomatic index (GSI) values were recorded in March for S. sihama (females: 0.653 ± 0.121; males: 0.351 ± 0.022) and in November for S. mengjialensis (females: 3.600 ± 0.371; males: 1.068 ± 0.115), indicating distinct and separate spawning seasons. In both species, males matured at smaller size, compared to females, with Lm₅₀ estimated at 93.73 and 98.76 mm for male and female S. sihama, and 86.00 and 128.14 mm for male and female S. mengjialensis, respectively. Histological examination identified immature and mature males and immature and maturing females in S. sihama, whereas mature males and fully ripe females were observed in S. mengjialensis. Fecundity in S. mengjialensis ranged from 8548 to 16,716 eggs per ovary. Feeding analysis revealed omnivory in S. sihama (RLG: 1.12) and carnivory in S. mengjialensis (RLG: 0.75). Length–weight relationships indicated positive allometric growth (b = 3.453) in S. sihama and isometric growth (b = 3.08) in S. mengjialensis. These findings provide important baseline data for future management, conservation, and stock assessment of these species.

Aquaculture in Uganda is mainly anchored on two fish species: Nile tilapia (Oreochromis niloticus) and the Ugandan African catfish (Clarias gariepinus). The Ugandan C. gariepinus is popular among farmers nationwide because of its desirable traits, such as high growth rates, a broad array of trophic levels, and resistance to diseases and parasites. Nevertheless, the species’ productivity is limited by insufficient molecular genetic data that can be used to inform selective breeding efforts. We fill this gap by sequencing the mtDNA D-loop of 192 C. gariepinus individuals from five major water bodies of Uganda. The results show that the Western Rift Valley lakes (Edward, George, and Albert) are more genetically diverse, with the least being the Central region lakes, particularly the Kyoga basin lakes. Fst values and the haplotype network group the C. gariepinus populations into two genetic clusters: the Western Rift Valley lakes (Albert, Edward, and George systems) and the Lakes Victoria and Kyoga systems. In particular, the current study reveals that Lakes Edward and George are likely a panmictic population. However, we noted genetic heterogeneity in L. Victoria, relatively indicating within-lake genetic structure. These results present the initial steps for genetically characterizing the Ugandan C. gariepinus populations and are key to guiding the use of the wild stocks in aquaculture for selective breeding programs to propel fish farming in Uganda.

The comprehensive 10-year fishing moratorium implemented in the Yangtze River Basin since 2021 provides a unique opportunity to evaluate the recovery of threatened fish populations. This study assessed the recovery status of Coilia nasus in the lower reaches of the Yangtze River during the fourth year of the moratorium through analysis of age structure, growth parameters, and sex ratio. Field investigations were conducted at two strategic locations (Chongming and Taizhou) during the migration season (May–June 2024), yielding 3077 specimens. Results revealed significant improvements in population parameters, including increased mean age (2.64 years) and standard length (28.5 cm), alongside a higher proportion of age 3 and age 4 individuals (63.3%). Sex ratio analysis showed a pronounced female bias (3.19:1), with spatial variations between estuarine (4.99:1) and upstream (2.04:1) sites. Growth parameter analysis indicated a shift toward natural growth dynamics, with increased asymptotic length (L_∞) and altered growth rates (k) compared to premoratorium periods. Despite these positive indicators, the absence of five-year-old individuals and lower average length compared to historical records suggest incomplete recovery. Our findings provide evidence for the effectiveness of the fishing ban while highlighting the need for continued protection.