Browsing by Author "Perera, H. A. C. C."

Now showing 1 - 4 of 4

Analyses of biometric growth parameters and feeding habits of Mugil cephalus (Flathead mullet): One of the economically important fish species collected from Negombo Lagoon
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Nimasha, N. T. P.; Perera, H. A. C. C.
Flathead mullet (Mugil cephalus) is found to be a potential candidate species in brackish water aquaculture due to its euryhaline nature, and it has ready markets for seeds as well as processed products. However, the lack of data on adult flathead mullets in the natural environment in Sri Lankan waters is the major constraint to study the biology of the species and management practices for fish resources. The present study was conducted to analyze the diet composition, length-weight relationship, and condition factor of M. cephalus belonging to the family Mugilidae collected from the Negombo lagoon, Sri Lanka. In fisheries science, the important condition factors are the growth, health state and feeding intensity. The sampling was done from August 2022 to March 2023. A total of 100 specimens were collected from the catches of artisanal fisheries from Negombo lagoon area. The total length and weight of fish were measured and varied in a range of 16.9 cm - 32.0 cm and 55.50 g - 291.70 g respectively. Length frequency distribution showed that the total length class 23 cm - 24 cm had the highest frequency of 100 samples. The FishBase reports length at first maturity as 30.0 cm and the percentage below 30 cm was observed as 97%. Results obtained showed a negative allometric growth pattern for this fish species (b<3, t-test, p< 0.05) with a significant linear relationship given by the equation; W = 0.0266TL2.690 (Log W = - 1.575 + 2.690 log TL (R2 = 0.951, n=100). Fulton’s condition factor (K) of males and females of M. cephalus was 1.0501 + 0.0359, and 1.0048 + 0.0123 respectively. Mean Fulton’s condition factor for immature mullets was lower than (0.9960 + 0.0724) that of the mature ones (1.0373 + 0.0735). Relative Gut Length (RGL) and Gastro Somatic Index (Ga.SI) were 1.52 – 3.18 and 2.012 – 3.874 respectively. The recorded mean RGL (2.442 + 0.146), confirmed that M. cephalus is omnivore species. The stomach content was analyzed using the frequency of occurrence method showed that algae (30.86%), sand particles (25.71%), and detritus (23.43%) as main food items. The food of animal origin consisted of annelids, insect parts and crustaceans. Most of the fish were one-fourth filled (1/4) at the time of capture. The immature individuals recorded from the Negombo lagoon area were 49 %. The present study reported the presence of synthetic debris such as nylon threads in the stomachs of flathead mullets revealing that the area is polluted. Therefore, more research into the effect of synthetic debris on the lagoon area is recommended. Continuous monitoring of fish landings is also recommended as immature individuals recorded were significant in the fish catch.
Analyses of biometric growth parameters, feeding ecology and fisheries aspects of Frigate Tuna (Auxis thazard), a Neritic Tuna species found off the east, west and south coasts of Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Rathnayaka, A. P. H. B.; Perera, H. A. C. C.; Perera, U. L. K.
Frigate tuna (Auxis thazard) is a commercially important neritic tuna species in Sri Lanka contributing to over 40% of the total neritic tuna catch of the country. Only a few studies have been conducted on biometric parameters of frigate tuna in Sri Lankan waters. Therefore, the present study was conducted to study the growth condition indices and fisheries aspects of A. thazard in selected coastal waters around Sri Lanka and the feeding ecology of A. thazard in the West coast of the country. The study was based on a primary data analysis where the data were collected from the West coast from November 2021 to February 2022 and a secondary data analysis in which the data were obtained from the Department of Fisheries and Aquatic Resources (DFAR) following the year 2017 for a comparative study off the Western, Southern and Eastern coasts of Sri Lanka. The Length–weight relationship (LWR) and Fulton’s condition factor (K) were estimated using the equations 𝑊 = 𝑎𝐿𝑏 and 𝐾=100𝑊/𝐿3 to assess the condition of the fish. The total weight ranged from 124.90 g -1405.05 g, 157.00 g -1475.00 g and 152.60 g - 890.40 g and further total lengths ranged from 23.8 cm - 44.2 cm, 21.5 cm - 46.5 cm and 25.5 cm - 44.1 cm for Western, Southern and Eastern coasts respectively. The LWRs were 𝑊= 0.0012𝑇𝐿3.6586, 𝑊 = 0.0026𝑇𝐿3.4846 and 𝑊 = 0.0147𝑇𝐿2.951, in which the pooled ‘b’ values 3.6586 and 3.4846 for the West and South coasts indicating positive allometric growth (b>3, t-test, p<0.05) and 2.951 for the East coast indicating isometric growth (b=3, t-test, p>0.05). Both male and female fish on each coast followed the same growth pattern without any difference. The K values 1.21 ± 0.42 and 1.43 ± 0.98 calculated for the West and South coasts indicated relatively healthy conditions and 0.94 ± 0.51 on the East coast indicated comparatively poor conditions. The gillnets accounted for 98% of catches on the West coast and ring nets accounted for 68% and 67% for South and East catches based on the total landings in 2017. In the primary data analysis, the estimated Relative Gut Length (RGL) confirmed the frigate tuna as a carnivore. The size classes of 30.0 - 31.50 cm and 23.50 - 24.50 cm had the highest and lowest feeding intensities based on the Gastro Somatic Index (GaSI). The most preferred prey item was shrimps. The Fishbase reports length at first maturity as 29.5 cm. The percentages below 29.5 cm include 18.83%, 39.18% and 33.99% for the West, South and East coasts, respectively. Therefore, continuous monitoring of fish landings and data collection is recommended for a sustainable fishery.
Analyses of biometric parameters, feeding, and fisheries aspects of Spotted Sardinella (Amblygaster sirm) occurring along the Negombo coastal waters of Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Wijesooriya, W. M. N. S.; Ratnayake, R. P. P.; Perera, H. A. C. C.
Amblygaster sirm is one of the major food fish in the small pelagic fishery in Sri Lanka. The study analyzed biometric parameters, feeding habits, and fisheries aspects of A. sirm in Negombo coastal waters. Two hundred A. sirm individuals were collected from the Negombo fish landing center and monthly interval from August 2022 to March 2023. The weight and total length of the collected fish ranged from 17.50 g - 109.00 g and 12.80 cm - 22.60 cm respectively. The lengthweight relationship (W=aLb) of males, females and pooled was W= 0.0029 TL 3.3546, W= 0.0035 TL 3.2819 and W= 0.0030 TL 3.3459. The significant deviation of the 'b' values from 3.0 indicates an allometric growth pattern for A. sirm in the coastal waters of Negombo (one-sample t-testp< 0.05). The Fulton’s condition factor (K) using the formula K = 100*W/TL, 0.9047 ± 0.1074, 0.94392 ± 0.08699 and 0.92331 ± 0.09995, for males, females and pooled respectively. The stomach-fullness of fish examined: were 40% empty, 15% one-fourth full, 12.5% half full, 27.5% three-fourth full, and 5% full stomach. Food and feeding analyses showed that ingested food includes 14.29% of phytoplankton including 1.53% of algae, 23.98% of mollusc larvae, 25.51% of crustacean larvae, 15.31% of fish eggs, 12.76% of arthropod appendages, 2.55% of synthetic fibers and 4.08% of unknown particles. According to the average Gastro Somatic Index, the highest and lowest feeding intensities using stomach fullness index were observed in the size class of 17.5 cm - 18.5 cm and 12.5 cm - 13.5 cm respectively. Their most preferred prey was crustacean larvae. The major vessel type used in fishing was Fiberglass Reinforced Plastic (OFRP) boats, operated within 15 - 20 fathom in depth. The small mesh drift gillnets with 31.75 mm and 38.1 mm mesh sizes was popular among the community. Of that, 38.1 mm mesh sizes are widely used. Synthetic materials in stomach content provide compelling evidence of the widespread contamination of marine ecosystems by human-made materials. The ingestion of these synthetic materials by fish poses a threat not only to their health but also to the overall ecological balance of marine habitats. Therefore, long term monitoring and research is recommended for the sustainable utilization of spotted sardinella fishery resources in Sri Lankan coastal waters.
Feeding habits of silky shark (Carcharhinus falciformis) landed in Negombo fishery harbour and an account on fishing vessels and gears used to catch them
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Karunanayaka, H. M. S. G.; Perera, H. A. C. C.
Silky shark (Carcharhinus falciformis) is one of the most common shark species captured as a target fishery or as by-catch in various regions in the world. Information about the feeding habits and predatory behaviour of silky sharks is important, as it determines the survival and abundance of other marine species, and also helpful in ecosystem management and sustainable utilization of shark fishery. The present study investigates the feeding habits of silky sharks and evaluates some aspects of the silky shark fishery based on 32 silky sharks caught by single-day and multi-day boats, and landed at the Negombo fishery harbor from August to September 2020. The total length of each silky shark landed was measured to the nearest 0.1 cm, and the body weight was measured to the nearest 0.1 kg using a measuring tape and an electronic balance respectively. Stomach samples of each shark were analysed for stomach contents and the extent of stomach fullness. Stomach contents were identified to the lowest possible taxon and grouped into three categories. Data on the vessel size, gear type, bait type, etc. used were collected by interviewing the multi- day and single-day boat skippers. Forty-eight (48) fishing vessels were observed during the study period. The total length (TL) of the sampled silky sharks ranged between 50-285 cm and weight ranged between 3.5-75 kg. Stomach fullness was classified under five categories; empty (40.6%), one-fourth filled (40.6%), half-filled (3.1%), three-fourth filled (6.3%) and full (9.4%). Occurrence of prey items in stomach contents were identified as fish remains (84.21%), arthropod remains (15.79%) and molluscan remains (5.26%). Milkfish (Chanos chanos), Amblygaster sp., Sepia sp., Decapterus sp., Auxis sp. and crab tissue segments. Of the 48 vessels inspected, 27.1% were single-day boats while 72.9% were multi-day boats. Higher percentage of silky sharks were caught by multi-day boats (77.6%) than by the single-day boats (22.4%). The boats were further identified as UN1, UN2A, UN3A and UN4 using standardized measurements. The fishing gears used by the boats were gillnet (45.8%) and longlines (54.2%). The number of silky sharks caught by longlines were higher (61.2%) than by gillnets (38.8%). The by-catch species caught in the fishing gear were identified as other shark varieties, billfishes and rays. The results of the present study also revealed that the diet of the silky shark mainly constitute of fish.