Triphoturus Mexicanus Research Articles

Fish larvae from the Gulf of California

SUMMARY: Taxonomic composition of fish larvae was analysed from 464 plankton samples obtained during 10 oceanographic surveys in the Gulf of California between 1984 and 1988. We identified 283 taxa: 173 species, 57 genera, and 53 families. Tropical and subtropical species predominated except during the winter, when temperate-subarctic species were dominant. The most abundant species were the mesopelagic Benthosema panamense, Triphoturus mexicanus and Vinciguerria lucetia, but the coastal pelagic species Engraulis mordax, Opisthonema spp., Sardinops caeruleus and Scomber japonicus were also prominent. The taxonomic composition of the ichthyoplankton shows the seasonality of the Gulf as well as environmental changes that occurred between the 1984-1987 warm period and the 1956-1957 cool period previously reported. The presence of E. mordax larvae as one of the most abundant species in the Gulf provides evidence of the reproduction of this species two years before the development of the northern anchovy fishery and the decline of the sardine fishery in the Gulf of California.

Ichthyoplankton distribution off the Peninsula de Mejillones, Chile (23° S, 71° W), under variable hydrographic conditions during the austral summer and winter of the 1997 El Niño

This paper identifies the larval fish community distribution, emphasizing non-commercial species, in the coastal zone and the adjacent oceanic area off the Peninsula de Mejillones (23° S, 71° W) during the 1997 El Nino. We performed one survey in the austral summer (January) and one in the austral winter (July). In January, cold, upwelled water dominated the area off the Peninsula de Mejillones with a cold-water filament extending 60 nm offshore. In July, warm Subtropical Surface Waters affected the area. We identified a total of 56 taxa, which included taxa from different adult habitats (coastal, epipelagic, epi-mesopelagic and mesopelagic). The most abundant species were Engraulis ringens (18% and 21%), Bathylagus sp. (4% and 5%), Diogenichthys laternatus(12% and 39%), Lampanyctus parvicauda (9% and 2%), Triphoturus mexicanus (14% and 3%) and Vinciguerria spp. (21% and 23%), in January and July, respectively. A multidimensional scaling (MDS) ordination and similitude dendograms revealed changes in the larval fish community structure influenced by hydrographic conditions. The rank correlations between the assemblage similarity matrix and the physical variables matrix indicate the importance of the distance from shore and production processes (represented by chlorophyll-a) on the assemblage distributions. Off the Mejillones' coast, there is a complex spatial and temporal hydrographic system where ichthyoplankton of coastal and oceanic fish species coexist. Despite both short-term and longer-term disruptive oceanographic processes (e.g., mesoscale filaments, El Nino events), it seems that the numerically dominant species persist in the area due to their various behavioral strategies and physiological adaptations.

Sinking rates and dissolution of midwater fish fecal matter

The sinking rates of fecal matter from 7 southern California midwater fish species were investigated. Feces were obtained from 162 specimens of Stenobrachius leucopsarus, Triphoturus mexicanus, Leuroglossus stilbius, Lampanyctus ritteri, Argyropelecus affinis and Parvilux ingens, which were collected in the Santa Barbara and San Clemente Basins between 1977 and 1979. In addition, feces obtained from 6 laboratory-maintained specimens of the midwater zoarcid Melanostigma pammelas were used for repeated sinking-rate measurements. The mean of the measured sinking rates for all species was 1.19 cm s-1 (1 028 m d-1), which is much higher than the known descent rates of euphausiid and copepod fecal pellets and of most other particulate organic detritus. Dissolution characteristics were also investigated for fecal matter from 4 species collected by the same series of net hauls: S. leucopsarus, T. mexicanus, A. affinis, and Sternoptyx obscura. The release of dissolved organic compounds from this material is low and does not represent a significant output during the relatively short time required to sink through the water column. These findings suggest that midwater fish fecal matter may represent a major source of organic transfer between the pelagic community and the benthos.

Comparison of the food of Triphoturus mexicanus and T. nigrescens, two lanternfishes of the Pacific Ocean

Prey (chiefly euphausiids and copepods) eaten by two myctophids (lanternfishes) are compared from incidence in fish stomachs and from abundance in the environment. One lanternfish species, Triphoturus mexicanus, lives in the California Current, and the other, T. nigrescens, lives in the central Pacific Ocean. Although these two environments are very different physically and biologically, the feeding habits of the two lanternfishes are surprisingly similar. Prey biomass is 94% euphausiids, 3% copepods, and 3% other organisms for T. mexicanus and 88% euphausiids, 4.5% copepods, and 7.5% other organisms for T. nigrescens; the difference between the fish species is not significant when tested statistically. The two fishes resemble one another in frequency distributions of ingested copepod individuals, copepod species, euphausiid individuals, and euphausiid species. During a single diurnal feeding period, both fishes eat a variety of copepod species but tend to eat only a single species of euphausiid. T. mexicanus grows to twice the length of T. nigrescens and eats proportionally larger euphausiids; however, both fishes eat copepods having the same median size. The frequencies of euphausiid species in the diets of both fishes differ from the frequencies in the environment. The chief differences between the feeding habits of the two lanternfishes are that T. nigrescens, in comparison to its congener, eats a greater variety of organisms during one diurnal feeding period and captures smaller euphausiids. The feeding patterns for each lanternfish species are consistent over distances of hundreds of kilometers and over many years of sampling.

Wax ester biosynthesis by midwater marine animals

Lipid is a major energy reserve in many aquatic animals, and wax esters are the principal type of lipid present in most pelagic marine invertebrates and teleost fishes from deep water or near-surface cold waters. It has been suggested that these wax esters are biosynthesized by only a few organisms, and are then transferred along the food web to the fishes and marine mammals. We found that accessible mesopelagic myctophid (Lampanyctus ritteri, Stenobrachius leucopsarus and Triphoturus mexicanus) and gonostomatid (Cyclothone atraria and Gonodtoma gracile) fishes and crustaceans (Gaussia princeps, Calanus helgolandicus, Acanthephyra quadrispinosa and Sergestes prehensilis) biosynthesize wax esters from acetate, longchain alcohol or fatty acid precursors, in vivo or in vitro. In the latter experiments, organ tissues (hepatopancreas and gut) are more active than muscle, although, overall, fish muscle is probably a major site of wax ester biosynthesis in the species studied. Therefore, wax esters are not persistent dietary survivors in the food web of the oceanic midwaters; rather, most invertebrates and fishes in this environment make wax esters, modifying ingested fats to their own characteristic patterns.

Distribution of the Midwater Fishes of the Gulf of California

A series of 203 midwater trawl hauls, most of which were discrete-depth samples, was taken at 126 trawling sites along nearly the entire length of the Gulf of California in 1967, 1968, and 1969. The resulting collection of 10,003 adult fishes has been analyzed as a representation of the community of midwater fishes which resides within the Gulf. A total of 39 species from 32 genera and 17 families were taken. In the collection, Triphoturus mexicanus was the dominant form (68%), followed by Vinciguerria lucetia (10.2%), Cyclothone spp. (8.2%), Diogenichthys laternatus (7.2%), and Benthosema panamense (2.8%). The bulk of the midwater community occupied a depth range between 300 and 400 m during daylight hours and from 50 to 100 m at night. The community is composed mainly of tropical forms but its proportional composition is unique to the Gulf. Water mass structure and surface water characteristics are considered as determinants

Accumulation of DDT residues in Triphoturus mexicanus from the Gulf of California.

CONTAMINATION of marine fish by chlorinated hydrocarbons, especially by DDT and its congeners*, could threaten their future or continued utility as a food source if residues accumulate to the point of incipient toxicity on detrimental sublethal effects1. Little is known about the distribution of DDT residues in marine fish beyond listed concentration values for certain species. Most investigations have dealt with concentrations of residues in tissues or large pooled, unsorted samples of commercially caught fish (refs. 3 and 4; the latter covers exclusively marine studies). From this limited information, we know that fish of a single species caught 111 adjacent areas have markedly different contents of residues, probably because of differences in the magnitude of local sources of estuarine or airborne pesticides2–5. This heterogeneity of exposure poses problems for the interpretation of residue data from fish caught in these areas. In an attempt to obtain size-class data about concentrations of residues, relatively free from the effects of pesticide “hot spots”6, Triphoturus mexicanus, a midwater fish from an area relatively remote from areas of pesticide application, was chosen for analysis.