Journal of Fisheries

Fecundity of giant freshwater prawn (Macrobrachium rosenbergii) varies with the trophic status and size of the inhabitant perennial reservoirs in Sri Lanka

RG Sanuja — 2025-07-29

Giant freshwater prawn (GFP, Macrobrachium rosenbergii) is an important commodity in the inland fisheries of Sri Lanka, where fecundity plays a crucial role in estimating the reproductive potential of the species. The fecundity of ovigerous GFP in relation to the trophic status and area of the reservoirs was empirically determined from the GFP collected from twenty-five dry-zone perennial reservoirs across Sri Lanka. Morphometric parameters, total and relative fecundity, and egg characteristics of ovigerous females were calculated. The total fecundity of GFP, which ranged between 5277±2069 – 29366±2371, differed significantly (p<0.05) with the trophic status and size of the reservoirs. The highest total fecundity was observed in the 24–25 cm and 185–210 g length and weight classes of GFP. The GFP inhabiting eutrophic medium perennial reservoirs exhibited the highest fecundity. Fecundity correlates with total length (r=0.75) and weight (r=0.71) of GFP. The total length of GFP was significantly associated with egg mass weight (r=0.74) in mesotrophic reservoirs compared to eutrophic reservoirs. Correlations between fecundity and body weight (r=0.70), fecundity and egg mass weight (r=0.76), egg mass weight and total length (r=0.69), and weight (r=0.72) were stronger in minor perennial reservoirs than in major and medium reservoirs. The present findings confirm that fecundity depends on the length, weight, and egg mass weight of ovigerous GFP, but not on the egg volume. The results align with the postulated hypothesis that the fecundity of ovigerous GFP varies with the trophic status and size of the reservoir.

Impacts of palmyrah (Borassus flabellifer) fruit pulp-enriched diets on growth and colouration of swordtail (Xipophorus helleri) and platyfish (Xipophorus maculatus)

Sutharshiny Sathyaruban — 2025-07-24

The ornamental fish industry urgently needs natural carotenoid sources due to the undesirable effects of synthetic additives. This study examines the effects of an untapped carotenoid source, palmyrah fruit pulp (PFP), on the growth and skin colour of swordtails (Xipophorus helleri) and platies (Xipophorus maculatus). Experimental diets containing 40% crude protein were formulated with varying PFP levels (%) at 0, 3, 6, and 8. A commercial diet was used as a positive control, while a diet without PFP was a negative control. Four-week-old swordtails (n=450) and platies (n=450) were divided into 15 groups for five treatments, and all were kept under the same conditions. The experiment lasted 81 days for the swordtail and 83 days for the platy. The findings show that the 8% PFP diet led to a significant increase in the skin colour in both fish compared to the other treatments. Higher growth performance (ANOVA: p<0.001) was observed in both fish when fed 3, 6, and 8% PFP diets compared to the negative control group; however, no significant difference from the positive control group. All treated groups had a survival rate of over 92%, and weight gains followed strong polynomial relationships (R²>0.98). The study concludes that an 8% PFP-enriched diet effectively influenced skin colour, with TCC levels of 85.59 µg g^–1 in swordtails and 80.54 µg g^–1 in platies. Furthermore, this diet promotes the growth of swordtails and platies. This diet serves as an adequate substitute for commercial fish feeds in the ornamental fish industry.

The tooth morphology of juvenile Pacific nurse sharks Ginglymostoma unami (Chondrichthyes: Ginglymostomatidae)

Jesco Seifert — 2025-07-17

Nurse sharks (family Ginglymostomatidae) are a small group of sharks that currently consists of four different species. These species are distributed all over the globe, each occupying a specific geographical region. The last described nurse shark species, the Pacific nurse shark (Ginglymostoma unami), is found exclusively on the West coast of America from the Southwest of Baja California and the Gulf of California (Mexico) to Peru. This species was previously synonymized with the Atlantic nurse shark (Ginglymostoma cirratum), but described as separate in 2015. For this reason, some data on tooth morphology, especially that of juvenile individuals, is missing. This study examines a jaw of a juvenile Pacific nurse shark and shows the change in the tooth morphology of this species over the course of its life. In addition, this work compares the tooth morphology of the different nurse shark species and provides an overview of how they can be differentiated.

Dietary emamectin benzoate alters the gill and spleen histoarchitecture of monosex Oreochromis niloticus fry

Jasmine Singha — 2025-07-07

Oral administration of the antiparasitic veterinary drug emamectin benzoate is recommended to control infectious ectoparasites, whose biosafety and effect on vital organs are unknown in several fish species. This study evaluated the influence of dietary emamectin benzoate on the histopathology of hitherto understudied organs, such as gills and spleen of all-male Oreochromis niloticus fry at the recommended dose of 50 µg and an overdose of 500 µg kg body weight^–1 day^–1 for 7 days. The fry recorded dose-dependent discrepancies in feed intake, survival and biomass. Histologically, noticeable pathological changes in the gill and spleen tissues were documented in both groups. The pathological alterations in the fry fed the recommended dose and increased severity in the overdosed groups indicated the toxic nature of emamectin benzoate and signified exercising caution during its application in tropical aquaculture.

Assessment of reproductive biology of Garra langlungensis (Teleostei: Cyprinidae) from the Langlung River, Nagaland, India

Sophiya Ezung — 2025-06-21

The stone sucker, Garra langlungensis Ezung, Shaingningam & Pankaj, 2021, is confined to the Langlung River, near Zutovi village in Dimapur district of Nagaland, India. This endemic fish is a common food item among the local people. There is scarce information available on this species. Despite its rising exploitation, the lack of data could contribute to its decline and potential loss. The present study involved analysis of 213 specimens from the Langlung River, collected monthly over a period of one year, to determine the sex ratio, gonadosomatic Index (GSI), and fecundity. The sex ratio of males to females was 1:0.43 (deviation from the expected 1:1 ratio), showing a male-dominated population. The monthly assessment of GSI indicated that G. langlungensis breed once a year, with maximum GSI values of 8.1 (male) and 11.5 (female) in April and a short breeding season extending from February to May. Fecundity, based on data from 16 mature fish specimens, was the highest (844 eggs) in 77.9 mm TL (0.56 g) and the lowest (319 eggs) in 55.2 mm TL specimen (0.23 g). A significant correlation between fecundity and ovary weight (r = 0.915) was recorded. This study provides insights into the sex ratio, GSI, and fecundity of G. langlungensis, which facilitate the identification of fish stocks in their natural habitats and the development of appropriate conservation measures.