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Size-related shifts in feeding habits of juvenile yellowfin tuna (YFT), Thunnus albacares (Bonnaterre, 1788), in Ecuadorian waters were assessed using stomach content analysis (SCA) (n = 339) and stable isotope analysis (n = 83). In all size classes, fishes were the predominant prey group in the diet (Alimentary Index, %AI = 96.86) followed by cephalopods (%AI = 3.29) and crustaceans (%AI = 0.03). PERMANOVA analysis revealed significant variations in diet with body size: i) Class I YFT (≤50 cm in fork length, FL) fed mainly on laternfishes, family Myctophidae (%AI = 37.34), and jumbo squid, Dosidicus gigas (%AI = 36.06), Class II YFT (50–60 cm, FL) consumed bullet and frigate tunas, Auxis spp., unidentifiable fish and jumbo squid (%AI = 47.75, %AI = 25.06 and%AI = 21.67, respectively), and Class III YFT (≥ 60 cm, FL) preyed almost exclusively on bullet and frigate tunas (%AI = 90.85). Mean ± SD muscle isotope values were 12.14 ± 1.95‰ for δ15N and −17.42 ± 0.27 for δ13C‰; mean (±SD) liver values were 11.30‰ for δ15N and −17.42 ± 0.27‰ for δ13C. Overall, liver and muscle samples showed significant size-related differences in δ15N and δ13C. Stable isotope Bayesian ellipses, SEAc, did not show trophic overlap among size classes. A significant positive linear correlation was observed between δ15N and δ13C measured in liver and muscle tissues with body size, suggesting an increase of prey size as tuna grew. These results indicate that the observed size-related diet shifts are not only related to prey type, but also to prey size.

Stomach content analysis (SCA) and stable isotope analysis (SIA), coupled with isotopic-mixing model analysis, were used to estimate diet composition of sailfish Istiophorus platypterus in eastern Taiwan waters. SCA provided information on diet, but the high occurrence of empty stomachs (48.5%) limited this analysis. According to the index of relative importance (%IRI), the most important prey items were Priacanthus macracanthus (38.7%), followed by Auxis spp. (35.9%), and Trichiurus lepturus (8.5%). However, the most important prey groups for adult sailfish (>181 cm, LJFL) as estimated by the stable isotope-mixing model were T. lepturus (32.6%), Katsuwonus pelamis (15.8%), and P. macracanthus (11.3%), and for maturing sailfish were K. pelamis (12.9%), P. macracanthus (10.4%), and T. lepturus (32.6%), respectively. Juvenile sailfish feed primarily on smaller prey items with lower δ15N values, while adult sailfish preferred larger prey items with higher δ15N values. Our findings suggested that an integrated SCA and SIA is considerably more powerful than using SCA alone in determining diet composition of sailfish over long time scales. In summary, a high diversity in the diet composition of sailfish was found and included an array of coastal, benthic, pelagic, and mesopelagic species. Sailfish are most likely opportunistic feeders consuming the most abundant prey items in eastern Taiwan waters.

Gel properties of croaker surimi blended with three types of mackerel surimi at different ratios were evaluated. The gel strength of the croaker–mackerel surimi blend was higher than that of the original mackerel surimi ( p p > 0.05). The addition of short-bodied mackerel surimi into croaker surimi up to a ratio of 1:2 had no effect on whiteness and metmyoglobin content of the gel ( p > 0.05). Marked decrease in expressible drip and TCA-soluble peptide of gel was noticeable in croaker–frigate mackerel surimi blend ( p

Critical gaps in our understanding of the distributions, interactions, life histories and preferred habitats of large and medium-size pelagic fishes severely constrain the implementation of ecosystem-based, spatially structured fisheries management approaches. In particular, spawning distributions and the environmental characteristics associated with the early life stages are poorly documented. In this study, we consider the diversity, assemblages, and associated habitat of the larvae of large and medium-sized pelagic species collected during 2 years of monthly surveys across the Straits of Florida. In total, 36 taxa and 14,295 individuals were collected, with the highest diversity occurring during the summer and in the western, frontal region of the Florida Current. Only a few species (e.g. Thunnus obesus, T. alalunga, Tetrapturus pfluegeri ) considered for this study were absent. Small scombrids (e.g. T. atlanticus, Katsuwonus pelamis, Auxis spp.) and gempylids dominated the catch and were orders of magnitude more abundant than many of the rare species (e.g. Thunnus thynnus, Kajikia albida ). Both constrained (CCA) and unconstrained (NMDS) multivariate analyses revealed a number of species groupings including: (1) a summer Florida edge assemblage (e.g. Auxis spp., Euthynnus alleterattus , Istiophorus platypterus ); (2) a summer offshore assemblage (e.g. Makaira nigricans, T. atlanticus, Ruvettus pretiosus, Lampris guttatu s); (3) an ubiquitous assemblage (e.g. K. pelamis, Coryphaena hippurus, Xiphias gladius ); and (4) a spring/winter assemblage that was widely dispersed in space (e.g. trachipterids). The primary environmental factors associated with these assemblages were sea-surface temperature (highest in summer-early fall), day length (highest in early summer), thermocline depth (shallowest on the Florida side) and fluorescence (highest on the Florida side). Overall, the results of this study provide insights into how a remarkable diversity of pelagic species spatially and temporally partition spawning within a region that is characterized by dynamic oceanography and strong habitat gradients.

Fronts and eddies are widely hypothesized to be critical spawning habitat for large pelagic fishes, due to increased larval and/or adult feeding opportunities at these features. We examined sailfish (Istiophorus platypterus) spawning around a cyclonic, submesoscale (∼13 × 7 km) Florida Current frontal eddy. The temporal progression of eddy dynamics over a 65 h period was determined using ocean color satellite imagery, continuous surface measurements along the cruise track, and non-linear least-squares fitting of the positions of three drifters deployed within the eddy. A peak in larval sailfish densities (n = 2435, stations = 49), composed primarily of yolk-sac and first-feeding larvae, occurred at the eddy frontal zone. A majority of these larvae were estimated to have been spawned during the formation of the eddy. A comparison between the distribution of similar-age sailfish and scombrid larvae indicated that the peak in larval sailfish density likely resulted from spawning directly at the front, rather than transport by convergent flow. The first-feeding prey items of larval sailfish (Farranula and Corycaeus copepods) were most abundant at the frontal zone and to a lesser extent inside the eddy. Egg distributions were used to indirectly assess the distribution of adult sailfish prey items. Euthynnus alleteratus and Auxis spp. eggs were in highest abundance outside the eddy, while the eggs of small carangids were in highest abundance at the eddy frontal zone. Overall, this study indicates that sailfish spawn at small-scale oceanographic features that provide a favorable feeding environment for their larvae and potentially also for the adults.

The fish remains are described that were found at the bottom of an Early Roman ceramic jar from Aila Aqaba, Jordan. The bones, representing the gill apparatuses of at least 33 medium-sized tunas (Auxis; Scombridae) and a single individual of a lizardfish (Trachinocephalus myops; Synodontidae), are believed to correspond to haimation. This highly prized fish sauce, documented previously only from ancient textual evidence, was typically made from the gills and the entrails of tunnids to which salt was added. The sauce was not imported from the Mediterranean or the Black Sea, but made from local Red Sea fish as shown by the zoogeographical distribution of the lizardfish that is considered as stomach content of the tunas. Because the fish bones were found in a locally produced jar and because the calculated volume of the haimation that the bones represent corresponds more or less to the volume of the jar, it is concluded that this high-quality garum was produced in this container at Aila itself.

The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was developed to identify the species of Thunnus thynnus , T . alalunga , T . obesus , T . albacares , Euthynnus pelamis ( Katsuwonus pelamis ), E . affinis , Auxis thazard and Sarda orientalis in products of canned tuna. To increase the efficiency and sensitivity of DNA extraction, a recent developed method of binding magnetic beads was applied in this study. Two sets of primer were designed to amplify 126 bp and 146 bp of partial mitochondrial cytochrome b gene, and five restriction enzymes including Bsp 1286I, Hin cII, Rsa I, Sca I and Mbo II were determined to analyze the short length fragments. The developed PCR-RFLP method was applied to authenticate species of 18 commercial canned tuna successfully, and it really provided a useful and academic technique to identify eight species in canned tuna.

Diet composition of the sailfish Istiophorus platypterus from the southern Gulf of California was determined using stomach contents of 576 fish. They were sampled from 1989 to 1991 from the sport fishing fleet at six tourist ports of the Mexican Pacific (La Paz, Cabo San Lucas, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo). A total of 78 different prey taxa was classified and 64 were identified to species. From the diet composition and using the percent of index of relative importance (IRI), three feeding zones were determined by using cluster analysis. The most important prey by zones were in Zone I, La Paz: Dosidicus gigas, Scomber japonicus, and Auxis spp.; Zone II, Cabo San Lucas: Auxis spp., Selar crumenophthalmus, and Lagocephalus lagocephalus; and Zone III, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo: Argonauta spp., D. gigas, and Auxis spp. We suggest that sailfish in Mexican Pacific waters are generalist predators feeding mainly on epipelagic species in coastal and oceanic waters, and occasionally diving to prey on demersal fish. The changes in diet composition among zones seem to be related more to abundance and distribution of the prey than to food preferences.

Collections of juvenile tunas during the period 1951–1960 from the central Pacific are recorded. Juveniles of Neothunnus macropterus (Temminck and Schlegel), Katsuwonus pelamis (Linnaeus), and Auxis sp. are described and figured. Initial results with the British Columbia midwater trawl, as modified for collecting tuna forage organisms and juvenile tunas, suggest that this trawl has considerable promise as a collecting device. Its ability to catch juvenile tuna appears much greater than that of the 10 ft Isaacs-Kidd midwater trawl. Although much has been learned in recent years abouth the biology of adult tunas, we still have very little information concerning the occurrence, distribution, and habits of their postlarval and juvenile stages. This lack is due mainly to poor success in collecting the young with the methods hitherto used, i.e., dipnetting at night-light stations, midwater trawling with small and medium-sized nets, seining with tuna bait nets, and searching the stomach contents of adult tunas and other pelagic fishes. Most of the juveniles recorded in the literature have been reported from scattered localities and have come either from the stomachs of pelagic fishes (Kishinouye, 1919, 1923, 1924, 1926; Inanami, 1942; Marr, 1948; Eckles, 1949; Shimada, 1951a; Yabe, Anraku and Mori, 1953; Yabeet al., 1958) or from dipnetting at nightlight stations (Schaefer and Marr, 1948a, 1948b; Wade, 1949, 1950; Shimada, 1951b; Klawe and Shimada, 1959). Since tuna juveniles are taken sporadically, generally in small numbers, it is important that all known captures be recorded so that the information will be available to investigators.