Reproductive cycle of northern largemouth bass Micropterus salmoides salmoides

Cold temperature delays ovarian development of largemouth bass by inhibiting sex hormone release, angiogenesis, apoptosis and autophagy during out-of-season reproduction

Cold temperature is an effective method of achieving out-of-season reproduction and obtaining fry in the autumn. This study investigated the effects of low-temperature (12-16 °C) environment on the out-of-season reproduction of largemouth bass, particularly the delayed effects on ovarian development. During the period of delayed out-of-season reproduction, there was a significant reduction in the levels of serum sex hormones (FSH and LH) and their respective receptors (FSHR and LHCGR). Exposure to cold temperature significantly reduced the expression of gonadal development genes (IGF-1, GDF9, and CDC2) (P<0.05) and diminished the vascular network on the ovarian membrane, as confirmed by angiogenesis-related analyses. In lipid metabolism, AMH mRNA levels decreased overall, while HSD3B, FABP1, APOA1, and APOC2 initially increased before declining. Serum VTG levels decreased gradually with a slight increase post-spawning. These findings suggested that cold temperature delay ovarian development in largemouth bass by impacting sex hormone synthesis, angiogenesis, and lipid deposition. This insight enhances our understanding of out-of-season reproduction and guides the development of more effective reproductive techniques.

Seasonal variations in gonadosomatic index and seminal quality of squirrel monkeys (Saimiri collinsi)

BACKGROUND

We hypothesized that seasonal variations in testicular biometry in Saimiri collinsi are influenced by body mass and that testicular enlargement is related to improved seminal quality. Therefore, the gonadosomatic index (GSI) can be a tool to determine reproductive seasons and the predictors of seminal quality.

METHODS

Body mass, testicular biometry, and semen samples were obtained from eight adult males monthly and evaluated.

RESULTS

In the non-fattening/non-reproductive season, the body mass and GSI decreased and increased, respectively, in the fattening. A positive correlation was only observed between the GSI and seminal volume. During fattening, high seminal volume and normal morphology were observed, but sperm concentrations were low.

CONCLUSION

The GSI cannot be used as a predictor of seminal quality, but selective pressure to improve seminal quality may increase the chances of fertilization at fattening. The GSI provides new information on seasonality and can be used to identify reproductive seasons in squirrel monkeys.

Timing of early gonadal differentiation and effects of estradiol-17β treatments on the sex differentiation in Largemouth bass (Micropterus salmoides)

In this study, an efficient estradiol-17β (E₂)-induced feminization method was established based on the timing of early gonadal differentiation in Largemouth bass (Micropterus salmoides). Histological section results showed that from 20 days post-hatch (dph) to 30 dph, the germ cells gradually differentiated into oogonium and spermatic deferent, respectively. Moreover, female-biased genes Foxl2 and Cyp19a1a were up-regulated to the first peak at 20 dph, while the male-biased genes Dmrt1 were up-regulated to the first peak at 30 dph. These results indicated that the timing of early gonadal differentiation in Largemouth bass was between 20 and 30 dph. Therefore, 15 dph Largemouth bass with a body length of 15.10 ± 0.09 mm were chosen, and four E₂-treated diets were set as 0 (E0, control), 50 mg/kg E₂ (E50), 100 mg/kg E₂ (E100), and 200 mg/kg E₂ (E200). After feeding with E₂-treated diets for 60 days, female ratios were 55%, 100%, 100%, and 100% in E0, E50, E100, and E200 groups, respectively. No intersex fish were observed in all the groups. However, 30% of females in the E200 group possessed thinner ovaries, with smaller ovary cavity structures and a decreased number of primary oocyte cells than those in other groups. Besides, the Largemouth bass in the E0 group grew more than those in E50, E100, and E200 groups during the E₂ treatments period (P < 0.05). In conclusion, our study suggested that 50-100 mg/kg E₂-treated diets could effectively induce the feminization of 15 dph Largemouth bass within 60 days duration time, which provided valuable information for the breeding of the all-male Largemouth bass population.

Nine Maxims for the Ecology of Cold-Climate Winters

Frozen winters define life at high latitudes and altitudes. However, recent, rapid changes in winter conditions have highlighted our relatively poor understanding of ecosystem function in winter relative to other seasons. Winter ecological processes can affect reproduction, growth, survival, and fitness, whereas processes that occur during other seasons, such as summer production, mediate how organisms fare in winter. As interest grows in winter ecology, there is a need to clearly provide a thought-provoking framework for defining winter and the pathways through which it affects organisms. In the present article, we present nine maxims (concise expressions of a fundamentally held principle or truth) for winter ecology, drawing from the perspectives of scientists with diverse expertise. We describe winter as being frozen, cold, dark, snowy, less productive, variable, and deadly. Therefore, the implications of winter impacts on wildlife are striking for resource managers and conservation practitioners. Our final, overarching maxim, “winter is changing,” is a call to action to address the need for immediate study of the ecological implications of rapidly changing winters.