The Effects of Temperature Acclimation on Swimming Performance in the Pelagic Mahi-Mahi (Coryphaena hippurus)

Mahi-mahi (Coryphaena hippurus) are a highly migratory pelagic fish, but little is known about what environmental factors drive their broad distribution. This study examined how temperature influences aerobic scope and swimming performance in mahi. Mahi were acclimated to four temperatures spanning their natural range (20, 24, 28, and 32°C; 5–27 days) and critical swimming speed (Ucrit), metabolic rates, aerobic scope, and optimal swim speed were measured. Aerobic scope and Ucrit were highest in 28°C-acclimated fish. 20°C-acclimated mahi experienced significantly decreased aerobic scope and Ucrit relative to 28°C-acclimated fish (57 and 28% declines, respectively). 32°C-acclimated mahi experienced increased mortality and a significant 23% decline in Ucrit, and a trend for a 26% decline in factorial aerobic scope relative to 28°C-acclimated fish. Absolute aerobic scope showed a similar pattern to factorial aerobic scope. Our results are generally in agreement with previously observed distribution patterns for wild fish. Although thermal performance can vary across life stages, the highest tested swim performance and aerobic scope found in the present study (28°C), aligns with recently observed habitat utilization patterns for wild mahi and could be relevant for climate change predictions.

Feeding Habits of Predatory Thermophilic Fish Species and Species with Subtropical Affinity from Recently Extended Distributional Range in Northeast Adriatic Sea, Croatia

The study investigates feeding habits of thermophilic species and species with subtropical affinity in the fishing catch in the Bay of Medulin (northeastern Adriatic Sea), and contributes to the knowledge about their presence in recently extended distributional range. In our methodology, the presence of the Seriola dumerili, Sphyraena sphyraena, Lichia amia, Coryphaena hippurus, Caranx crysos, Pomatomus saltatrix, and incidence of Trachinotus ovatus is recorded. A total of 220 specimens are captured during 2017, 2018 and 2019. A dietary assessment is performed, and the index of relative importance IRI was calculated for each prey category. Diet overlap is calculated using Schoener’s index, based on IRI. The principal diet of C. hippurus included Sardina pilchardus and Loligo vulgaris. Pomatomus saltatrix consumed species from the Sparidae family and T. ovatus crustaceans from the Mysidacea family. Different species from genus Atherina are represented important foods for L. amia, S. dumerili and S. sphyraena. Diets of significant importance for L. amia included fishes from the family Sparidae, for S. sphyraena from the Carangidae family, and S. dumerili from the Clupeidae and Muliidae families. Our analysis of diet overlap is based on IRI suggests no diet overlap between analysed fish species from Medulin Bay, and that these species utilise differing trophic niches.

Kerentanan Species Ikan Retain pada Perikanan Tuna dari Alat Tangkap Handline

Kelompok ikan retain dari perikanan tuna juga termasuk kelompok komersial utama yang juga banyak dimanfaatkan. Penurunan hook rate tuna juga turut mempengaruhi perikanan tuna termasuk hasil tangkapan samping lainnya. Untuk itu penelitian kerentanan kelompok retain ini juga perlu dilakukan untuk mengetahui potensi berkelanjutannya. Penelitian dilakukan pada bulan Juli 2013 di Sendangbiru Malang, Bitung, Wakatobi, dan Kendari. Data yang dikumpulkan dan kemudian dianalisis adalah produkitivitas dan susceptabilitas menurut kriteria MSC (Marine Steward Council). Indek kerentanan dievaluasi dari indek jarak (Index Jaccard). Hasil tangkapan ikan retain dari perikanan tuna adalah ikan cakalang (Katsuwonus pelamis), ikan lemadang (Coryphaena hippurus), dan baby tuna (Thunnus albacores). Nilai produktivitas berkisar 1.43-2,14 tergolong sedang sampai tinggi dan susceptibilitas 1,13-1,48. Tingkat kerentanan ikan retain berkisar 86,3-96,2 yang tergolong rentan rendah (low risk) dan potensial berkelanjutan.

Edible films gelatin-based obtained from mahi-mahi skin (Coryphaena hippurus) and oregano extract: Physicochemical, antimicrobial, structural and surface characteristics

Edible films were elaborated from gelatin solutions (4% w/v) of mahi-mahi skin (Coryphaena hippurus) with 2,5; 5; 7,5 and 10% v/v of oregano extract (OE) and its physicochemical, antimicrobial, structural and surface properties were determined. The control and with 2.5% OE films showed the lowest moisture and opacity values and the highest viscosity values. All films with OE inhibited the growth of Staphylococcus aureus and Proteus vulgaris. Alone films with 10% OE showed antimicrobial activity against all the strains evaluated. Scanning electron microscopy showed that the incorporation of oregano extract in the film-forming solutions, FFS, was related to an increase in the presence of oil droplets in the films, showing the lipid fraction of OE. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyzes showed the interaction between gelatin, plasticizer, and oregano extract in all films. In conclusion, this study demonstrated the viability of mahi-mahi skin gelatin edible films with OE incorporated for their application as packaging with antimicrobial action in foods susceptible to spoilage by microorganisms.

Projected effects of ocean warming on an iconic pelagic fish and its fishery

Increasing sea temperature is a driver of change for many fish traits, particularly for fast-growing epipelagic species with short life spans. With warming, altered spawning phenology and faster growth may produce substantially larger body sizes of the new cohort, affecting fishery productivity. We present an individual-based model (IBM) that predicts the distribution of fish length at catch under observed and projected thermal scenarios, accounting for mortality, temperature-dependent spawning phenology, temperature- and photoperiod- dependent growth. This IBM was demonstrated with Coryphaena hippurus (common dolphinfish), a circumglobally-distributed and highly thermophilic species sustaining commercial and recreational fisheries where it is present. The model projected a 13.2% increase in the average length at catch under marine heatwave conditions compared to the current thermal regime (1995–2005 average). Projections under RCP scenarios 4.5 and 8.5 by the end of the century led to 5.1% and 12.8% increase in average length, respectively. Furthermore, these thermal scenarios affected spawning phenology differently, producing higher variance in body size under RCP 8.5 scenario with respect to marine heatwave conditions. This study highlights how the environmental effects of climate change can alter the distribution of species length at catch.

Reproductive traits in dolphinfish Coryphaena hippurus Linnaeus, 1758 along the coastal waters of Karnataka, south-eastern Arabian Sea

The maturity, sex ratio, gonadosomatic index (GSI) and fecundity of Coryphaena hippurus was investigated from 347 specimens collected along Karnataka coast, south-eastern Arabian Sea from August 2017 to May 2018. Overall sex ratio of 1:3.5 (male:female) indicated dominance of females in the fishery and differed significantly (p<0.05) in all the months, except in January, May and December. The fork length (FL) at 50% maturity (Lm50) was estimated at 47.5 cm for both males and females. The pattern of GSI and maturity stages suggests peak spawning activity in August-September. However, the incidence of fishes capable spawning all through the year in varied proportions implied that spawning activity occurs throughout the year. The absolute fecundity estimates varied from 1,00,298 eggs for a female of 53.5 cm FL to 6,15,267 eggs for female of 113 cm FL with an average fecundity of 3,18,446 eggs per female. Thefecundity of fish increased with body length and weight as well as with gonad weight. The biological information on maturation, reproductive cycle, spawning periodicity and fecundity of C. hippurus in the tropical Arabian Sea could be useful for developing appropriate management tools and conservation strategies for this commercially important fish species.

Remote Predictions of Mahi-Mahi (Coryphaena hippurus) Spawning in the Open Ocean Using Summarized Accelerometry Data

Identifying complex behaviors such as spawning and fine-scale activity is extremely challenging in highly migratory fish species and is becoming increasingly critical knowledge for fisheries management in a warming ocean. Habitat use and migratory pathways have been extensively studied in marine animals using pop-up satellite archival tags (PSATs), but high-frequency data collected on the reproductive and swimming behaviors of marine fishes has been limited by the inability to remotely transmit these large datasets. Here, we present the first application of remotely transmitted acceleration data to predict spawning and discover drivers of high activity in a wild and highly migratory pelagic fish, the mahi-mahi (Coryphaena hippurus). Spawning events were predicted to occur at nighttime, at a depth distinct from non-spawning periods, primarily between 27.5 and 30°C, and chiefly at the new moon phase in the lunar cycle. Moreover, throughout their large-scale migrations, mahi-mahi exhibited behavioral thermoregulation to remain largely between 27 and 28°C and reduced their relative activity at higher temperatures. These results show that unveiling fine-scale activity patterns are necessary to grasp the ecology of highly mobile species. Further, our study demonstrates that critical, and new, ecological information can be extracted from PSATs, greatly expanding their potential to study the reproductive behavior and population connectivity in highly migratory fishes.