Ambient Photoperiod Research Articles

Spontaneous recurrence of a summer-like diel rhythm in the body temperature of the Syrian hamster after hibernation.

Mammalian hibernation is a survival strategy characterized by metabolic suppression and drastically lowering body temperature (Tb), used during harsh seasons with food shortages and cold. The Syrian hamster commences hibernation in response to a short photoperiod and cold but spontaneously concludes hibernation after several months without environmental cues. Little is known about the changes in diel rhythms during hibernation. Using long-term and high-resolution Tb data, we analysed the diel Tb rhythm time-course changes in Syrian hamsters raised under summer-like conditions (long photoperiod (LP) and warm; LP-warm) and transferred to winter-like conditions (short photoperiod (SP) and cold; SP-cold). The diel Tb rhythm was undetectable during the hibernation period (HIBP), reappearing after the HIBP. The phase of this returning rhythm reverted to the LP entrainment phase characteristics despite the ambient SP and then re-entrained to the ambient SP as if the hamsters were transferred from the LP-warm to SP-cold conditions. The diel Tb rhythm reverted from the SP- to LP-type in a hibernation-dependent manner. Under constant dark and cold conditions, the circadian Tb rhythm recovered without photic stimuli following the HIBP. These findings suggest that hibernation involves a program that anticipates the ambient photoperiod when animals emerge from hibernation.

Photoperiodism and overwintering in boreal and sub-Arctic Calanus finmarchicus populations

The copepod Calanus finmarchicus, a key species in the North Atlantic, generally spends the non-productive season by descending into deep waters and entering diapause, a physiological state characterized by reduced metabolism and arrested development. In the open ocean, overwintering depths are below 600 m, where temperature and light conditions are favourable to initiate diapause. However, C. finmarchicus has also been reported diapausing in areas with shallow water depth such as fjords, coastal waters and shelf seas. In these environments, the temperature and light conditions are different, and it has been hypothesized that under such conditions C. finmarchicus may remain active throughout winter. Here, we investigated changes in the swimming activity of C. finmarchicus from shallow fjords in the eastern North Atlantic during overwintering in response to ambient photoperiod. We conducted monthly experiments with populations from 2 fjords from different latitudes (sub-Arctic Ramfjord, 69°N and boreal Loch Etive, 56°N), measuring the locomotor activity of individual C. finmarchicus stage CVs exposed to a natural light:dark cycle. At both locations, peaks in activity in response to the light cycle were observed to shift from nocturnal during the early overwintering phase to diurnal during mid and late overwintering phase, with a minimal intensity observed during the mid-overwintering phase. In Ramfjord, activity and rhythmicity were generally lower than in Loch Etive. We conclude that C. finmarchicus remains active throughout its overwintering period when in shallow (<200 m) locations but down-regulates its locomotor activity during the main overwintering phase, which we describe as a winter resting state as distinct from classical diapause.

PSV-A-8 Reduced Daylength pre-Calving Increases Milk Production Post-Calving

Abstract Exposing Holstein dry cows to short-day (SD) photoperiod of 8 hours per day can improve milk production post-calving by 3.2 kg per day, compared to cows exposed to long-day (LD) photoperiod of 16 hours per day during the same period. To date, no studies have evaluated the effect of altered photoperiod during the dry period on milk production in Jersey cows. Our objective was to study the effect of LD and SD during the dry period on milk production in both breeds. Holstein and Jersey cows (n=33) dried off 60 days prior to their due date were exposed to either SD (n=9 Holstein, n=8 Jersey) or LD (n=8 Holstein, n=8 Jersey) at 18.3 °C until calving. After calving, cows returned to ambient photoperiod and milk data was collected for 15 weeks. Lactation number, replicate, dry period feed intake and days of treatment were recorded. Data were analyzed using PROC MIXED in SAS 9.4. Overall average milk production differed by breed (P< 0.01), with Holsteins producing more (72.9 ± 6.2 kgs) than Jerseys (66.1 ± 7.3 kgs). Treatment differed (P=0.02) with SD cows producing more milk (71.0 ± 6.9 kgs) than LD cows (68.1 ± 6.7 kgs). Treatment and breed interaction significantly differed. Long-day Holsteins produced 73.9 kgs ± 6.2 kgs which was not different (P >0.10) from SD Holsteins (72.1 ± 6.4 kgs). Neither LD nor SD Holsteins differed significantly (P=0.16, P=0.60) from SD Jerseys which produced 70.0 ± 7.4 kgs. Long-day Jerseys averaged the least milk at 62.3 ± 7.3 kgs which was significantly different from all other groups (P< 0.01). This data suggests Jerseys’ milk production responds similarly to previous reported Holstein data. Factors causing the unexpected Holstein data could be elevated temperature-humidity index values post-calving, despite industry standard heat abatement.

Conditions to Terminate Reproductive Diapause of a Univoltine Insect: Ceratapion basicorne (Coleoptera: Apionidae), a Biological Control Agent of Yellow Starthistle.

Ceratapion basicorne (Illiger) is a recently approved univoltine biological control agent that develops inside the rosette of yellow starthistle (Centaurea solstitialis L.), an invasive annual plant. Adult weevils normally emerge in early summer, and females are thought to be in reproductive diapause until the following spring, when they oviposit in rosettes. The long period of reproductive diapause constrains mass-rearing this weevil because only one generation per year can be produced. Determining the environmental conditions that regulate diapause termination may enable shortening diapause under laboratory conditions to increase production of adults to release. We tested three hibernating conditions (greenhouse [ambient temperature and photoperiod], glass door refrigerator [5°C and ambient photoperiod], and growth chamber [5°C and 24 h dark]) for three durations (4, 8, 11 wk). The highest proportion of females laying eggs came from the growth chamber, with 40% terminating diapause after 4 wk, 80% after 8 wk, and 95% after 11 wk of exposure. Our study demonstrates that duration of cold temperature is an important stimulus to terminate reproductive diapause of C. basicorne, and that exposure to ambient light had no effect at 5°C. However, 47% of females held at ambient greenhouse conditions, without any chilling period, completed diapause within 11 wk. Thus, a cold period can accelerate diapause development, but it is not necessary for its completion. Reducing the winter diapause period from about 6 mo to 11 wk should enable the production of multiple generations per year to increase the number of insects available to release.

The Effect of Non-Circadian Photoperiod on Growth and Puberty Onset of Brook Trout Salvelinus fontinalis Mitchill.

Simple SummaryThere has been intensive research addressing the positive effects of different prolonged photoperiods on wide spectrum of aspects of salmonids aquaculture. The present study was an attempt to assess non-circadian photoperiod regimens on growth and puberty onset of brook trout. We found regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light to be remarkably effective on the delay of gonad development and onset of puberty, enabling fish farmers to fight with negative aspects related to brook trout puberty.The aim of the present study was to assess the effects of a prolonged photoperiod on growth rate and sexual maturation in brook trout Salvelinus fontinalis. The task of the experiment was to determine the most effective light regimen capable to minimizing the effects of puberty, including impairment of somatic growth and further general characteristics. In this regard, the studied fish were reared under three photoperiod regimens in which fish were exposed to 24 h continuous light alternating with 24 or 48 h under the ambient photoperiod or 48 h continuous light alternating with a 24 h ambient photoperiod. A control group was reared under the natural ambient photoperiod. Four-hundred and fifty fish with an average initial body weight of 101.3 ± 1.2 g were used for each experimental group (three replicates of each treatment plus control). A statistically lower growth rate showed control groups in both sexes. At the end of the study, control males had an average body weight of 226.6 ± 39.8 g and control females a body weight of 199.8 ± 12.2 g. At the same period, a significantly higher average body weight was found in groups reared 24 h under ambient photoperiod alternating with a 48 h continuous light regime (2CP:1AP) in both sexes (296.56 ± 62.5 g—males, and 239.9 ± 19.2 g—females, respectively). A significantly higher percentage of sexually mature fish was observed in the control group (80% of males and 29% of females, respectively). We found significantly fewer sexually mature females compared to males. The lowest survival was observed in group 2CP:1AP at 92%. It was concluded that regimen under which fish was exposed to 48 h of natural ambient photoperiod alternating with 24 h of constant light (1CP:2AP) lead to the successful delay of gonad development and onset of puberty and increased somatic growth in both sexes.

Reproductive management of the transitional mare

The mare is a seasonally polyoestrous long-day breeder with a physiological breeding season lasting from April–October in the Northern Hemisphere. The hypothalamic-pituitary-gonadal axis in the mare is subject to a circannual endogenous rhythm that is primarily regulated by day length. Increasing ambient photoperiod in the spring alters the pattern of melatonin secretion. The resulting stimulation of hypothalamic gonadotropin-releasing hormone secretion triggers pituitary follicular stimulating hormone release and follicular growth. Exposure of mares in deep anoestrus to a stimulatory photoperiod remains the most successful method of advancing the first ovulation of the season. The most commonly used lighting regimen is providing a fixed length of 15–16 hours of light exposure and 8–9 hours of dark, with a minimum light intensity in a stable of 100-lux (100–200 watt incandescent bulb). Other methods include using an additional 2.5 hours of light beginning at sunset and a pulse lighting system, providing 1 hour of light, 9.5–10.5 hours after the onset of darkness, during the photosensitive phase. Alternatively, the EquilumeTMlight masks provide a unilateral LED light source emitting 50 lux of blue-light directly to the eye during the hours after dusk (until 11 pm). Mares that have not been maintained under lights, or that have been exposed to ineffective light therapy, may require therapeutic hormonal intervention to advance the onset of the first ovulation of the season. Many hormone protocols involving progestins, GnRH, dopamine agonists and recombinant luteinising hormone/follicle stimulating hormone have been studied with variable results. Therapy is typically more effective when started either in late transitional mares or following a period of stimulatory artificial photoperiod.

Reproductive management of the transitional mare

The mare is a seasonally polyoestrous long-day breeder with a physiological breeding season lasting from April–October in the Northern Hemisphere. The hypothalamic-pituitary-gonadal axis in the mare is subject to a circannual endogenous rhythm that is primarily regulated by day length. Increasing ambient photoperiod in the spring alters the pattern of melatonin secretion. The resulting stimulation of hypothalamic gonadotropin-releasing hormone secretion triggers pituitary follicular stimulating hormone release and follicular growth. Exposure of mares in deep anoestrus to a stimulatory photoperiod remains the most successful method of advancing the first ovulation of the season. The most commonly used lighting regimen is providing a fixed length of 15–16 hours of light exposure and 8–9 hours of dark, with a minimum light intensity in a stable of 100-lux (100–200 watt incandescent bulb). Other methods include using an additional 2.5 hours of light beginning at sunset and a pulse lighting system, providing 1 hour of light, 9.5–10.5 hours after the onset of darkness, during the photosensitive phase. Alternatively, the EquilumeTM light masks provide a unilateral LED light source emitting 50 lux of blue-light directly to the eye during the hours after dusk (until 11 pm). Mares that have not been maintained under lights, or that have been exposed to ineffective light therapy, may require therapeutic hormonal intervention to advance the onset of the first ovulation of the season. Many hormone protocols involving progestins, GnRH, dopamine agonists and recombinant luteinising hormone/follicle stimulating hormone have been studied with variable results. Therapy is typically more effective when started either in late transitional mares or following a period of stimulatory artificial photoperiod.

Maternal Photoperiodic Programming: Melatonin and Seasonal Synchronization Before Birth.

This mini-review considers the phenomenon of maternal photoperiodic programming (MPP). In order to match neonatal development to environmental conditions at the time of birth, mammals use melatonin produced by the maternal pineal gland as a transplacental signal representing ambient photoperiod. Melatonin acts via receptors in the fetal pituitary gland, exerting actions on the developing medio-basal hypothalamus. Within this structure, a central role for specialized ependymal cells known as tanycytes has emerged, linking melatonin to control of hypothalamic thyroid metabolism and in turn to pup development. This review summarizes current knowledge of this programming mechanism, and its relevance in an eco-evolutionary context. Maternal photoperiodic programming emerges as a useful paradigm for understanding how in utero programing of hypothalamic function leads to life-long effects on growth, reproduction, health and disease in mammals, including humans.

Photoperiodic regulation in a wild-derived mouse strain.

Mus musculus molossinus (MSM) is a wild-derived mouse strain which maintains the ability to synthesize melatonin in patterns reflecting the ambient photoperiod. The objective of this study was to characterize the effects of photoperiodic variation on metabolic and reproductive traits, and the related changes in pituitary-hypothalamic gene expression in MSM mice. MSM mice were kept in long (LP) or short photoperiod (SP) for 6 weeks. Our results demonstrate that MSM mice kept in LP, as compared to mice kept in SP, display higher expression of genes encoding thyrotropin (TSH) in the pars tuberalis, thyroid hormone deiodinase 2 (dio2) in the tanycytes, RFamide-related peptide (RFRP3) in the hypothalamus and lower expression of dio3 in the tanycytes, along with larger body and reproductive organ mass. Additionally, to assess the effects of the gestational photoperiodic environment on the expression of these genes, we kept MSM mice in LP or SP from gestation and studied offspring. We show that the gestational photoperiod affects the TSH/dio pathway in newborn MSM mice in a similar way to adults. This result indicates a transgenerational effect of photoperiod from the mother to the fetus in utero. Overall, these results indicate that photoperiod can influence neuroendocrine regulation in a melatonin-proficient mouse strain, in a manner similar that documented in other seasonal rodent species. MSM mice may therefore become a useful model for research into the molecular basis of photoperiodic regulation of seasonal biology.

Day length predicts investment in human immune function: Shorter days yield greater investment

Winter is characterized by stressful conditions which compromise health and render animals more vulnerable to infection and illness than during other times of the year. Organisms are hypothesized to adapt to these seasonal stressors by increasing investment in immune function in response to diminished photoperiod duration. Here, we examined this hypothesis in a sample of healthy human participants. Using several functional immune assays in vitro, as well as by utilizing measures of in vivo proinflammatory cytokine levels, we predicted that shorter day length would be associated with greater investment in immunological function. Results revealed that shorter days predicted significant upregulation of several facets of immune function, including natural killer cell cytotoxicity, peripheral blood mononuclear cell proliferation (in response to, and in the absence of stimulation), and plasma levels of interleukin-6, as well as lower rates of Staphylococcus aureus growth in serum ex vivo. Further, consistent with the hypothesis that these trade-offs would be offset by decreased investment in mating effort, shorter day length also predicted lower levels of total testosterone in men. These results suggest that ambient photoperiod may be a powerful regulator of human immunological activity, providing some of the first evidence of seasonal changes in multiple facets of human immune function.

The effect of timing of extended photoperiod on growth and maturity of brook trout ( Salvelinus fontinalis )

The influence of timing of extended photoperiods on growth and maturity of brook trout was investigated in a 112-day experiment. The fish with mean initial weight of ~192 g were reared under four light regimes: one control group with natural ambient photoperiod and three groups exposed to an 18L:6D regime initiated at days 1, 23 or 46 of the growth trial. Light-emitting diodes, with intensity of 250–1000 lux, depending on the distance from the light source, were used for extending light periods. There was a positive effect of prolonged day length on fish growth (p < 0.05), and a delay in gonad development and sexual maturity. Significantly higher numbers of sexually mature fish were found among controls groups, regardless of sex. Survival rate was not affected by light regime. This study demonstrated that the short-term expansion of the photo period delayed maturation and increased the growth rate of brook trout.

The effects of a prolonged photoperiod and light source on growth, sexual maturation, fin condition, and vulnerability to fungal disease in brook troutSalvelinus fontinalis

The effects of an artificially prolonged photoperiod on growth, survival rate, colouration, and sexual maturation in brook trout Salvelinus fontinalis during pre- and post-spawning periods from 21 June to 06 November were investigated. Fish of mean initial weight ˜150 g were reared at ambient photoperiod as well as with an artificially prolonged photoperiod produced by either a light-emitting diode or a metal-halide light. The fish groups subjected to a prolonged period of artificial light grew significantly larger and had a higher survival rate (p < 0.05), regardless of sex, and showed lower occurrence of fungal disease compared to controls reared in the natural photoperiod. We found a significantly higher number of sexually mature fish in the control groups compared with experimental groups. The increased photoperiod effectively delayed gonad development and increased somatic growth in both male and female brook trout, and also increased resistance to fungal disease. The increased photoperiod produced an observable difference in fish colouration, with control groups exhibiting more intensive spawning colouration.

The Life Cycle of Caligus minimus on Seabass (Lates calcarifer) from Floating Cage Culture

Caligus minimus, known as a sea louse, is a very important pathogen of sea floating cage culture. This paper describes the life cycle of Caligus minimus isolated from seabass culture in the cage in Penang, Malaysia. The parasitic copepod development was observed at 30 °C and 20 °C, with ambient photoperiod under laboratory conditions. Female of Caligus minimus with matured eggs were collected and incubated in a beaker with slow aeration. The life cycle consists of nine stages: two nauplii, one copepodid, four chalimi, pre-adult, and adult. The copepodid is infective, and all subsequent stages were attached to fish and did not require an intermediate host for its development. The eggs hatched out within 48 h at 30 °C and within 60 h at 20 °C, and two nauplii stages were recorded after 1.88 ± 0.74 h and 4.23 ± 1.02 h, respectively. Copepodid stage was informed after 24.91 ± 2.24 h. A single experiment conducted by exposing an uninfected sea bass fingerling to copepod showed the copepodid immediately attached to the body, fins, and gills of the fish. Chalimus stage was observed after 20.95 ± 3.70 h followed by pre-adult stage after 45.88 ± 5.95 h. Within 44.5 ± 1.08 h, the adult was found and showed the female became mature and lay the eggs after 43.25 ± 3.11 h. At 20 °C, Copepodid was recorded after 25.86 ± 1.40 h and completed Chalimus stage within 40 h. Conclusively, 5.5–10 days were needed for Caligus minimus to complete its life cycle at tested temperature.

ARACHIDONIC ACID IN THE DIET OF CAPTIVE CALIFORNIA YELLOWTAILSeriola dorsalisAND ITS EFFECTS ON EGG QUALITY

AbstractMarine finfish require long-chain polyunsaturated fatty acids (LC-PUFAs) for normal physiological function, and because these LC-PUFAs cannot be synthesized by the fish they must be obtained from the diet. Three LC-PUFAs—arachidonic acid (ARA; c20:4 n-6), eicosapentaenoic acid (c20:5 n-3) and docosahexaenoic acid (c22:6 n-3) are especially important for growth and development of marine fish embryos and larvae. Here we supplemented ARA in the diet of California yellowtail (CYT; Seriola dorsalis), to determine whether ARA levels have an effect on egg and larval quality.Two experimental diets were offered to replicate groups of CYT held in 10 m3 tanks under ambient water temperature and photoperiod conditions. The reference diet (REF-D; 1.4 g ARA 100 g−1 total fatty acids) was a commercial premix (Bio Vita Starter Mash; Bio-Oregon) without ARA supplementation, the ARA diet (ARA-D; 4.7 g 100 g−1 total fatty acids) was the commercial premix with 1.0% concentrated ARA oil (40% ARA, w/w) added.Fish in th...

Ovarian development of captive F1 wreckfish (hāpuku) Polyprion oxygeneios under constant and varying temperature regimes – Implications for broodstock management

In order to better understand how photo-thermal conditions affect oogenesis in captive-bred F1 hāpuku, a wreckfish considered for aquaculture in New Zealand, juvenile (pre-pubertal) fish were assigned to one of two regimes: exposed to a constant temperature of 17°C (CT group) or to seasonally varying temperatures (VT group range: 10–17°C), both under simulated ambient photoperiod, for nearly 2years. Development in females was monitored through repeated gonadal biopsies (histology; target gene mRNA levels) and blood sampling (plasma levels of estradiol-17β; E2). Very little evidence of advancing oogenesis was found in the first year of study, when fish were in their 4th year. In the subsequent year, a proportion of fish reached the pre-spawning stage (fully-grown ovarian follicles); the proportion of females reaching this stage was notably higher in the VT (62%) than the CT (28%) group. Of the few females that did reach maturity in the CT group, significantly lower levels of plasma E2 were observed relative to those in fish from the VT group possibly indicating a temperature-induced endocrine impairment during oogenesis. Interestingly, females that did not reach the pre-spawning stage presented with a small transient, but significant increase in oocyte diameters and plasma E2, suggestive of a dummy run. Clear seasonality was observed for fish under both photo-thermal regimes, and this was reflected in plasma E2 levels and transcript abundances of aromatase, fshr and luteinizing hormone receptor in the ovary; these end points all peaked in maturing females during the late or post-vitellogenic stage. We conclude that captive female F1 hāpuku first mature as five-year-olds and that exposure to a decreased temperature is important for appropriate progression of oogenesis.

Growth and Development of Two Perennial Grasses in Ambient Light Conditions during their Natural Dormant Period

Phenological and morphological behaviors under variable temporal and spatial environmental conditions provide essential information for breeding native perennial warm‐season grasses for bioenergy and ecosystem goods and services. Among various environmental factors, natural photoperiodic signals can affect both vegetative and reproductive growth of perennial species. In this study, field‐collected plants of switchgrass (Panicum virgatum L.) and prairie cordgrass (Spartina pectinata Link) were subjected to ambient photoperiods of either increasing or decreasing daylength during the dormant period of their normal growth cycles in a temperature‐controlled greenhouse. Upland switchgrass reacted to a short‐day treatment (decreasing or increasing daylength &lt;12 h) with a less synchronized dormancy‐breaking pattern than prairie cordgrass. Prairie cordgrass showed a strict daylength overriding dormancy‐breaking pattern. However, phenological and morphological traits observed during the growing season through reproductive development and senescence indicated that the capacity to reach sexual maturity for both species was not greatly affected by subjection to noninductive photoperiod immediately after breaking dormancy. Overall, our results indicated that switchgrass coped with unfamiliar natural photoperiod conditions better than prairie cordgrass in terms of vegetative and reproductive growth.

Effect of fish vitellogenin on the growth of juvenile catfish, Clarias gariepinus (Burchell, 1822)

The effect of heterologous fish vitellogenin (Vg)- implantation on growth performance in the juveniles of the catfish, Clarias gariepinus, was evaluated under ambient photoperiod and temperature during February–April (experiment 1) and again at May–August (experiment 2). Compared to either unimplanted (control) or bovine serum albumin (BSA)-implanted group, juveniles (average body weight: 3.5–4g) implanted (im) with Vg pellets (each containing 100μg of Clarias batrachus Vg, three per fish, at one month interval), revealed significantly (P<0.05) higher specific growth rate (SGR) at 90days during both time frames. Congruent with accelerated somatic growth due to Vg-implantation, a trend of increase in plasma level of growth hormone (GH), estradiol-17β (E2) and testosterone (T) was recorded during expt. 1. While plasma E2 and T did not vary significantly, Vg-implantation promoted significant (P<0.05) increase in plasma GH level in both the sexes during the course of expt. 2. Moreover, Vg-implantation could trigger significant alteration in gonadal growth; while control testis contained primarily spermatogonia (SG) and spermatocytes (SC), appearance of spermatozoa (SZ) was noticed in either Vg-implanted (expt. 1) or both BSA- and Vg-treated juveniles (expt. 2). Conversely, a robust increase in S III yolky oocytes was observed in Vg-implanted ovary during May–Aug; but not during expt. 1 (Feb–Apr). However, oocytes at earlier stages (S I and/or S II) of follicular growth and development were predominant in control ovary. Though the underlying mechanism is not yet clearly understood, present data indicate that implantation of Vg pellets in juvenile C. gariepinus may influence somatic growth indices; e.g., body weight gain and GH synthesis along with precocious gonadal growth in a manner sensitive to gonadal steroidogenesis.

Seasonal variation in the profile of sex steroids and histological testicular development of brook trout (Salvelinus fontinalis Mitchill) during the annual reproductive cycle in Tasmania

Early maturation in brook trout males has been a constraint for commercial production of this species in Tasmania. However, control of maturation in males can be achieved by manipulating photoperiod (duration of light phase). To design an appropriate light treatment regime, an assessment of the annual reproductive cycle was initially required under ambient photoperiod as the annual reproductive cycle of male brook trout under ambient Tasmanian conditions of light and temperature was unknown. Here we describe the seasonal variations in testicular development and plasma profiles of testosterone (T), 11-ketotestosterone (11-KT) and oestradiol-17β (E2) during the second year in a male brook trout cohort held under ambient light conditions. Brook trout males were recruited for maturation in December when a reduction in daylength presumably stimulated testicular development. Increases in levels of T, 11-KT and gonadosomatic index (GSI) values were observed soon after the summer solstice, corresponding with maturation. The highest GSI mean value (3.44 ± 0.11%) was observed in April when mature males could be manually stripped of milt and such males were present until July. Profiles of sex steroids and histological development observed in this study were finely synchronised with variations in seasonal photoperiod changes. Photoperiod before recruitment during December should be controlled to manipulate maturation in brook trout males during their second year.

Full replacement of menhaden fish meal protein by low-gossypol cottonseed flour protein in the diet of juvenile black sea bass Centropristis striata

Eight isonitrogenous (46% crude protein) and isolipidic (14% crude lipid) diets were formulated for juvenile black sea bass Centropristis striata to replace menhaden fish meal (FM) protein (59.5% CP) by three cottonseed meal (CSM) proteins: a CSM prepared from glandless seed (GCSM, 50.4% CP), a CSM that had been solvent extracted with acidic ethanol to remove the gossypol (SCSM, 53.8% CP), and a CSM prepared from regular (glanded) cottonseed (RCSM, 45% CP). Three diets replaced 50, 75 and 100% of FM protein with GCSM, and three diets replaced 50, 75 and 100% of FM protein with SCSM. One diet replaced 100% FM protein with RCSM protein. A control diet (0% CSM) was formulated with high FM protein and other practical protein sources. l-methionine and l-lysine were supplemented to the diets to equal the control diet. Fifteen fish were stocked in each of twenty-four 75-L tanks, and each test diet was fed to triplicate groups of fish (mean initial weight=7.7±0.10g) for 56days at 22–24°C, 32–35 salinity, and ambient photoperiod conditions. Fish were fed twice per day to apparent satiation. Final (day 56) mean body weight (BW, 24.16–31.62g), body weight gain (BWG, 211.2–311.3%), specific growth rate (SGR, 1.70–2.18%/d), and feed intake (FI, 0.37–0.43g/fish/d) were not significantly different (P>0.05) among the control, GCSM or SCSM treatments, but were reduced (P<0.05) for the 100% RCSM treatment (20.09g, 159.5%, 1.45%/d, and 0.25g/fish/d, respectively). Lower palatability of the RCSM diet was attributable to the anti-nutrient compound gossypol. No significant differences in survival (84.1–97.8%), feed conversion ratio (FCR, 1.05–1.33), protein efficiency ratio (PER, 1.62–2.08), or whole body protein or lipid composition were observed among the fish fed the low-gossypol diets. Gossypol (25.9mg/kg) was only detectable in the livers of fish fed the high-gossypol RCSM diet. Fish whole body essential amino acid compositions did not differ significantly among treatments. Whole body n − 3 PUFAs decreased, while n−6 PUFAs increased with increasing CSM protein in the diets. The apparent digestibility coefficient of protein was high (83.1–87.1%) for all treatments. For juvenile black sea bass, 75% FM in the diet can be replaced with low-gossypol CSM protein prepared by solvent-extraction, and 100% of FM can be replaced with low-gossypol CSM protein prepared from glandless seed with no adverse effects on survival, growth or feed utilization. Statement of relevanceCotton seed flour is an inexpensive agricultural by-product. The results demonstrate successful replacement of fish meal protein with genetically-improved cottonseed flour protein in the diet of black sea bass. These findings may substantially lower aquafeed costs (a key operational cost) for finfish growout operations to boost profitability and accelerate expansion of commercial production of black sea bass and other finfish species.

Evidence for a Role of Prolactin in Mediating Effects of Photoperiod during the Dry Period.

Photoperiod manipulation during the lactation cycle alters milk yield, with long days (LDPP) increasing yield in lactation and short days (SDPP) in the dry period improving subsequent yield. Circulating prolactin (PRL) is directly related to day length, with LDPP increasing and SDPP decreasing PRL, respectively. Two blocks of 24 multiparous Holstein cows were used during two consecutive years to test the hypothesis that the mammary response to SDPP is the result of decreased concentrations of PRL in the circulation relative to LDPP. Cows were randomly assigned to one of three treatment groups during the dry period: SDPP, LDPP, or SDPP+PRL. Cows were returned to ambient photoperiod at calving and milk yield and DMI recorded for 120 d and 42 d, respectively. Mammary biopsies were obtained to determine rates of [3H]-thymidine incorporation into DNA in vitro. Treatment of SDPP cows with PRL caused a rapid increase in systemic PRL that reached concentrations similar to cows under LDPP. The periparturient PRL surge was similar for LDPP and SDPP+PRL cows, but those groups had greater surge concentrations versus SDPP. Cows exposed to SDPP produced more milk than LDPP cows, and there was a trend for SDPP+PRL cows to produce more milk than LDPP cows. Milk production was inversely related to the periparturient PRL surge. There was a trend for a treatment effect on mammary cell proliferation with greater proliferation in mammary tissue of SDPP cows relative to LDPP or SDPP+PRL on day −20 relative to parturition. Replacement of PRL to cows on SDPP when dry resulted in milk yield intermediate to cows on SDPP or LDPP, supporting the concept of a link between dry period PRL and yield.