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9 recordsLinked to original sources
USGS2020

Developmental ecomorphology of the epibranchial organ of the silver carp, Hypophthalmichthys molitrix

Silver carp regularly consume and digest particles of food as small as 5 μm. This ability drives their efficient consumption of phytoplankton and because they feed low on the food chain they have an important place in aquaculture worldwide. In North America, where they are considered invasive, silver carp deplete food resources for native species and in so doing occupy increased niche space. Here, we determine the ontogenetic stage and size at which silver carp are morphologically capable of primarily feeding on particles <10 μm. Ecological studies on this species have shown that there is an ontogenetic shift in diet as predominantly zooplanktivorous juveniles later switch to eating much smaller phytoplankton. The occupation of this new trophic niche presents both a metabolic and a mechanical challenge to these fish, since it is unclear how they can efficiently feed on such small particles. We hypothesize that the epibranchial organ (EBO) in silver carp is essential in aggregating these small particles of food, allowing the species to consume mass quantities of tiny particles, thus mitigating metabolic constraints. In this study, we investigate early ontogeny of the EBO in silver carp to determine when this structure achieves the requisite morphology to become functional. We find that at around 80 mm standard length (SL) the EBOs are consistently filled with food, demonstrating that this accumulating organ has become functional. This size corresponds with previous ecological data documenting important shifts in the type of food consumed. While the basic bauplan of the EBO is established very early in ontogeny (by 15 mm SL), multiple waves of histological maturation of muscle, cartilage, gill rakers and epithelium ultimately form the functional structure.

Journal of Fish Biology↗
USGS2019

First examination of diet items consumed by wild-caught black carp (Mylopharyngodon piceus) in the U.S.

Black carp ( Mylopharyngodon piceus ) were imported to the U.S. in the 1970s to control snails in aquaculture ponds and have since escaped from captivity. The increase in captures of wild fish has raised concerns of risk to native and imperiled unionid mussels given previous literature classified this species a molluscivore. We acquired black carp from commercial fishers and biologists, and examined digestive contents of 109 fish captured over 8 y from lentic and lotic habitats in the central and southern U.S.A. Digestive tract contents were preserved, and diet items inventoried. We identified 59 aquatic animal taxa (21 mollusks, 27 insects, and 11 other invertebrates) and various plant material including nuts and seeds; no fish were found. Approximately 45% of stomachs examined were empty or only contained flukes (Trematoda) that had infected mollusks before they were ingested. Nonempty stomachs contained snails (16.5%), bivalve mussels (22.8%), and insect larvae (net-spinning caddisflies, 15.6%; burrowing mayflies, 6.4%; and midges, 13.7%). Fish also consumed freshwater sponges (Porifera), moss animals (Bryozoa), crustaceans (Ostracoda and Decapoda), water mites (Acarina), and three worm phyla (Nematoda, Nemertea, Annelida). Seven taxa of unionid mussels were identified from shell fragments among the fish we examined, all of which are found in habitats with soft mud or sand/silt substrates. Diet of fish captured in lentic environments contained significantly higher richness than those captured in lotic environments. Individual black carp often contained large numbers of only one or two diet items that were assumed locally abundant and did not always crush the shells of mollusks. Most fish we examined consumed benthic prey, which supports the classification of black carp as a benthic foraging species. However, the presence of other aquatic taxa associated with pelagic or subsurface zones suggests black carp are opportunistic in their consumption of diet items and flexible in their feeding modes.

The American Midland Naturalist↗
USGS1986

Tissue distribution and elimination of radiolabelled methyltestosterone fed to adult blue tilapia

Radioactivity levels in 10 tissues were monitored for 21 days after adult (1-year-old) blue tilapia, Oreochromis aureus , were fed a single meal of a diet containing 30 μg unlabelled methyltestosterone (MT) per gram of feed and radiolabelled MT ( 3 H-labelled steroid nucleus and 14 C-labelled 17α-methyl group). Radioactivity was highest in all tissues 6–12 h after the feeding; about 90% of the radioactivity was in the digestive tract, liver, gall bladder, and kidney. Radioactivity declined nearly 90% by 4 days and only 0.5% of original radioactivity (67 ng/g of fish) remained after 21 days. Half of the remaining exogenous hormone was in digestive and excretory tissues; concentrations in muscle were less than 1 ng/g of tissue. Ratios of 3 H: 14 C in tissues were similar to those incorporated in the diet and suggested that the 17α-methyl group was not removed during metabolism.

Aquaculture↗
USGS2003

Phosphorous digestibility and activity of intestinal phytase in hybrid tilapia, Oreochromis niloticus X O. aureus

Experiments were conducted to determine the degree to which phytate-bound phosphorus from plant protein sources could be used by hybrid tilapia (Oreochromis niloticus X O. aureus). Utilizing an inert marker technique with chromic oxide, hybrid tilapia in our study were effective at utilizing both inorganic and phytate phosphorus as evidenced by average apparent digestibility values of 93.2% and 90.0% for total and phytate phosphorus, respectively. Analysis of the intestinal brush border membrane of the tilapia revealed enzyme activity that was capable of hydrolyzing phytic acid. The presence of phytic acid hydrolyzing enzyme activity in the intestinal brush border provides a probable mechanism by which these hybrid tilapia are able to utilize phytate phosphorus effectively. ?? 2003 by The Haworth Press, Inc. All rights reserved.

Journal of Applied Aquaculture↗
USGS1988

Assessment of lupin flour as a diet ingredient for rainbow trout (Salmo gairdneri)

Studies were conducted to determine the value of lupin flour as a replacement for full-fat soybean meal (FFSM) in the diet of rainbow trout ( Salmo gairdneri ). Energy and digestibility values for lupin were determined using a metabolism chamber and it was found that trout utilize lupin well. The gross energy, metabolizable energy, and the percent digestibilities of protein and energy for lupin were found to be 4757 kcal/kg, 2797 kcal/kg, 85.2%, and 66.1%, respectively. When plant protein (either FFSM or lupin flour) was used as a supplemental dietary protein source to fish meal, or when the plant protein was the primary dietary protein source, fish fed diets where lupin completely replaced FFSM gained 99–106% of the weight of those fed the FFSM and had statistically equal feed efficiency ratios ranging from 80 to 83%. Although some minor dietary alterations may be needed (e.g., lowering the fat content of the diet) to maintain the economic advantage of lupin over soybean meal, lupin appears to be a useful source of protein for trout and may represent another economical plant protein alternative to fish meal.

Aquaculture↗
USGS2022

The development of genetic sex identification markers and evidence of a male heterogametic sex determination system in Red Shiner

The Red Shiner Cyprinella lutrensis is of increasing management interest as an invasive species that negatively impacts many native fishes throughout North America. Trojan sex chromosome (TSC)-carrying individuals could theoretically control invasive fish populations by skewing the sex ratio to 100% male. The efficacy of TSC-based control programs requires an understanding of a population's sex determination system, yet such information is lacking for Red Shiner. We used single-digest restriction site-associated DNA sequencing to discover sex-linked single-nucleotide polymorphisms (SNPs), and we conducted a series of breeding experiments to uncover the sex determination system. All candidate sex-linked SNPs that fit our selection criteria exhibited a pattern of male heterogamety. We developed two sex-identification (sex-ID) marker assays, XY_248 and XY_170, which showed phenotype–genotype concordance scores of 77.00% and 84.35%, respectively. These sex-ID markers exhibited relatively high phenotype–genotype concordance in females (XY_248 = 96.30%; XY_170 = 98.61%), which allowed for selective breeding of phenotypically feminized genetic males. We observed a 3:1 male : female sex ratio in spawns from feminized males crossed with wild-type males, indicative of a male heterogametic sex determination system (i.e., XY male/XX female). The discovery of a male heterogametic sex determination system, in combination with our two markers, increases the likelihood of developing an effective TSC eradication strategy for invasive Red Shiner populations.

North American Journal of Aquaculture↗